Carbon Sequestration as a Framework for Urban Facility Planning in Benin Metropolis, Nigeria

Carbon Sequestration as a Framework for Urban Facility Planning in Benin Metropolis, Nigeria | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Systematic Review Carbon Sequestration as a Framework for Urban Facility Planning in Benin Metropolis, Nigeria Jolly Osaretin EGHAREVBA This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8173067/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 11 You are reading this latest preprint version Abstract Cities contribute heavily to climate change but also hold solutions. This study examines how urban facilities in Benin Metropolis, Nigeria, can act as carbon sinks. A systematic review and meta-analysis, guided by PRISMA protocols, were conducted. Evidence was drawn from global, regional, and Nigerian studies on five facility types (green infrastructure, public buildings, transport, waste, and water systems). Findings show that green infrastructure and waste management are the most immediate and cost-effective strategies. They sequester carbon while tackling urgent urban problems like flooding, sanitation, and heat stress. In the medium to long term, mass timber construction, bio-based materials, electrified transport, and constructed wetlands offer transformative benefits. The study develops a framework combining Urban Political Ecology, the Circular Bioeconomy, and Sustainable Urban Development Theory. This highlights that carbon sequestration is not only technical but also political and social. Governance, justice, and local participation shape outcomes as much as technology. For Benin Metropolis, ecological opportunities exist, but governance weaknesses, outdated codes (building code, urban planning regulations, and energy and transport standard), and limited finance are major barriers. The study concludes that carbon sequestration should become a central principle of urban facility planning. Embedding it into facilities can shift Benin Metropolis from a net carbon source to a carbon sink. This approach also aligns with Nigeria’s Climate Change Act (2021) and global sustainability goals. Carbon Sequestration Urban Facility Planning Green Infrastructure Community Engagement Sustainable Urban Development Climate Mitigation Figures Figure 1 Figure 2 Figure 3 1. Introduction Cities today stand at the epicentre of the climate crisis, simultaneously representing both the source of the problem and the key to its solution. Globally, urban areas account for more than 70% of energy-related carbon dioxide (CO₂) emissions, despite covering only about 3% of the Earth’s land surface (IPCC, 2022). This concentration of emissions arises from the dense clustering of human activity, energy consumption, transport systems, industrial production, and construction. Yet, as centres of innovation, cities also hold the potential to lead the world towards climate solutions, particularly by rethinking how urban facilities are planned and managed. Rather than being passive emitters of carbon, urban spaces can be designed to act as carbon sinks through deliberate integration of carbon sequestration strategies. The urgency of such a paradigm shift is most evident in Africa, where urbanisation is unfolding at one of the fastest rates globally. By 2050, the continent’s urban population is projected to more than double, reaching nearly 1.4 billion (OECD et al., 2025). Nigeria, Africa’s most populous nation, epitomises this transformation. With over 223 million people in 2023 and a projected 400 million by 2050, Nigeria faces immense demographic pressures (World Bank, 2023 ). Cities such as Lagos, Abuja, Kano, and Benin Metropolis are experiencing unprecedented growth, driven by rural–urban migration and natural population increases. Yet this growth is often unregulated, producing sprawling settlements, infrastructural deficits, and heightened environmental degradation (Jiboye et al., 2020 ). In the heart of Edo State, Benin Metropolis stands as both a cultural hub and a city under intense environmental pressure. Accelerated urbanisation has come at the cost of deforestation, wetland loss, rising housing demand, unsustainable waste practices, and growing vehicular emissions. The removal of trees for residential estates has drastically reduced natural carbon sinks, while reliance on carbon-intensive materials such as cement and steel has deepened emissions. Furthermore, poor waste management practices, with organic waste dumped in open sites, generate methane that compounds climate impacts (Ike et al., 2018 ). These processes have left the city grappling with recurrent flooding, worsening heat stress, air pollution, and rising vulnerability for its poorest residents (Ede, 2019). Globally, urban sustainability debates are shifting from a narrow focus on emission reduction to a broader paradigm that combines reduction with active carbon removal and storage. This is the essence of carbon sequestration or “carbon gaining.” While traditional urban planning has prioritised efficiency better energy use, improved mobility, and enhanced waste management the scale of accumulated greenhouse gases now demands strategies that actively lock carbon away (Egharevba, 2025 ). Carbon sequestration encompasses the capture and storage of atmospheric CO₂ in vegetation, soils, and building materials. When embedded in urban systems, facilities such as public buildings, transport corridors, waste plants, and wetlands can be reimagined to function simultaneously as service providers and carbon sinks (Churkina et al., 2020 ). This perspective reframes urban facilities as active agents in climate action. Mass timber construction, for instance, locks carbon into buildings while reducing reliance on high-emission materials (Singh et al., 2022 ). Urban forests and street trees absorb CO₂ while cooling neighbourhoods and enriching biodiversity. Composting and anaerobic digestion convert waste into soil carbon and renewable energy, while wetlands treat wastewater and sequester carbon in biomass and soils. Taken together, these interventions suggest that cities like Benin can transition from “carbon-losing” to “carbon-gaining.” The case for Benin Metropolis is particularly compelling. Unlike megacities such as Lagos, Benin reflects the realities of medium-sized African cities which is fast-growing, under-researched, and often overlooked in policy design (Cobbinah & Niminga-Beka, 2017 ). Its medium scale offers flexibility for experimentation and innovation before infrastructural path dependencies become locked in (Parnell & Pieterse, 2014). Yet the city’s fragmented governance, informal settlements, weak enforcement of planning laws, and financial constraints mirror systemic challenges across sub-Saharan Africa. Nigeria’s climate commitments have intensified the urgency for sustainable urban transformation. As a signatory to the Paris Agreement, the country has pledged to achieve net-zero emissions by 2060 (Federal Government of Nigeria, 2021 ). However, progress toward this target remains uneven across sectors. In the energy sector, for instance, recent studies reveal conflicting trends efforts to promote a low-carbon energy transition coexist with continued investment in fossil fuel infrastructure, leading to persistent CO₂ emissions. Technological barriers, including ageing power grids, weak research and innovation capacity, and dependence on imported technologies, further slow the transition. Financial challenges such as poor fiscal policy implementation, weak investment frameworks, corruption, and limited access to renewable energy funding compound these problems (Atedhor, 2025 ). These national-level constraints are reflected in urban contexts, where inadequate financing, fragmented institutions, and limited technical capacity hinder the adoption of low-carbon strategies. Within this landscape, Benin Metropolis presents a critical opportunity to demonstrate how carbon sequestration can be effectively integrated into urban facility planning, aligning local actions with Nigeria’s broader climate goals and the global pursuit of sustainable development. This study responds to a critical gap in both scholarship and practice. While global evidence on urban carbon sequestration is expanding, research in sub-Saharan African cities remains sparse and fragmented. Strategies proven in temperate regions cannot be assumed to succeed in African contexts marked by constrained resources, institutional fragility, and socio-economic inequalities (Omokaro, 2025 ). By undertaking one of the limited systematic reviews and meta-analyses of carbon sequestration strategies in Nigerian cities, this research makes an original contribution. It synthesises international lessons while adapting them to the realities of Benin Metropolis, thereby providing a context-specific framework for action. The objectives are of threefold, first, to review global and African strategies for integrating carbon sequestration into urban facilities such as green infrastructure, sustainable buildings, transport, waste, and water systems; second, to contextualise these strategies within Benin’s socio-economic, ecological, and governance landscape; and third, to develop an integrative framework to guide policymakers, planners, and communities. The significance of this study lies in its dual contribution. Academically, it advances debates on sustainable urbanism by embedding carbon sequestration within African urban contexts. Practically, it offers policymakers in Benin Metropolis and similar medium-sized cities a roadmap for transforming facilities into carbon sinks. Beyond climate mitigation, the co-benefits including reduced flooding, improved air quality, cooling, livelihoods, and public health make the case for urgent action. Ultimately, the study emphasises that the future of Benin Metropolis is not predetermined. With deliberate choices, it can emerge as a carbon-gaining, resilient city that advances both Nigeria’s net-zero ambitions and global debates on sustainable urban futures in the Global South. 2. Theoretical Framework Every research endeavour rests upon conceptual foundations that guide its arguments, sharpen its analytical lens, and lend coherence to its findings. For this study, three interlinked paradigms are mobilised: Urban Political Ecology (UPE), the Circular Bioeconomy, and Sustainable Urban Development Theory. Together, these frameworks provide a multidimensional perspective on how urban facilities in Benin Metropolis currently function, how they may be re-imagined as carbon sinks, and what political, economic, and ecological conditions shape this transformation. 2.1 Urban Political Ecology (UPE) Urban Political Ecology (UPE) emerged in the 1990s as an extension of political ecology into urban contexts, interrogating how power, politics, and inequality underpin the production of urban environments (Tzaninis et al., 2021 ; Silva et al., 2024 ). It challenges the perception that environmental issues in cities are purely technical or natural. Instead, it emphasises that they are deeply political rooted in decisions about who benefits from development, who bears environmental costs, and how resources are allocated (Swyngedouw & Heynen, 2003). Applied to Benin Metropolis, UPE reveals the political-economic dynamics underlying its carbon-intensive growth. The replacement of forests and wetlands with housing estates is not merely a response to population pressures but also reflects governance decisions that prioritise short-term revenue from land allocation and speculative real estate development over long-term ecological resilience. Similarly, failures in waste management are not only technical inefficiencies but reflect power struggles between local authorities, private contractors, and informal waste pickers (Egharevba &Onaiwu, 2020 ). These governance tensions persist despite Nigeria’s Climate Change Act (2021), which mandates emission reduction targets and institutional frameworks for climate action. UPE highlights how weak enforcement of this legislation at the city level risks undermining national ambitions, as fragmented urban governance leaves room for elite capture and marginalisation of vulnerable groups. UPE also illuminates the unequal distribution of environmental burdens. In Benin Metropolis, low-income residents disproportionately live-in flood-prone areas with inadequate drainage and minimal green cover. These communities face the highest risks from flooding, heat stress, and poor air quality while contributing the least to emissions (Heynen et al., 2006 ; Akinyemi & Ogunleye, 2021). This resonates with UPE’s central claim: urban environmental crises mirror broader socio-political inequalities. From this perspective, transforming facilities into carbon sinks is not simply about technical fixes but about addressing governance and justice concerns. Unless interventions are designed inclusively, carbon sequestration projects could reproduce or even intensify inequalities for example, displacing informal settlers to create green spaces. By tying these insights to Nigeria’s evolving climate governance, UPE grounds the study in the reality that achieving the Climate Change Act’s carbon budgets depends on aligning national frameworks with local justice and accountability mechanisms. In this study, UPE therefore provides a critical lens to ask: Carbon for whom? Who gains and who loses from carbon-gaining facilities? These questions ensure that strategies are not only ecologically effective but also socially just, anchoring climate action in equity and fairness. 2.2 The Circular Bioeconomy Concept While UPE foregrounds politics and justice, the Circular Bioeconomy offers a complementary economic ecological paradigm. Broadly, the bioeconomy refers to the use of renewable biological resources such as forests, crops, and organic waste to produce food, energy, and materials. When combined with circular economy principles, it moves beyond the traditional linear “take–make–dispose” model towards one where biological materials are reused, recycled, and regenerated (Korhonen et al., 2018 ). For Benin Metropolis, this paradigm provides practical strategies for integrating carbon sequestration into everyday facilities. In buildings, the use of mass timber or bamboo locks carbon for decades, reducing dependence on cement and steel, whose production is highly carbon-intensive (Churkina et al., 2020 ). In waste management, composting and anaerobic digestion transform organic waste streams from methane emitters into carbon sinks and renewable energy sources (Bernstad & la Cour Jansen, 2012 ). In water infrastructure, constructed wetlands recycle wastewater while sequestering carbon in soils and biomass (Retta et al., 2023 ). The Circular Bioeconomy resonates strongly with African contexts. In Benin Metropolis, informal recycling, composting, and urban farming are already widespread, though often marginalised from official policy. By formally recognising and supporting these practices, planners could enhance both carbon sequestration and livelihoods (Orobator & Adahwara, 2022 ). Here again, connections to the Climate Change Act (2021) are instructive: while the Act sets national emission reduction goals, the Circular Bioeconomy demonstrates how grassroots resource efficiency can be scaled and integrated into governance frameworks to operationalise those goals. Importantly, the Circular Bioeconomy challenges the notion that sustainability must be costly. Instead, it highlights efficiency, innovation, and value creation from waste. By reframing biological systems as economic assets, it opens pathways for green entrepreneurship, job creation, and more resilient urban economies in Nigeria. 2.3 Sustainable Urban Development Theory The third pillar of this framework is Sustainable Urban Development Theory, which argues that cities can and must grow in ways that balance economic expansion, environmental protection, and social equity (Campbell, 1996 ). It provides the normative foundation for sustainable urban planning, insisting that urban development should not come at the expense of ecological integrity or social well-being. In Nigeria, however, urban development has historically emphasised economic growth over sustainability. In Benin Metropolis, housing estates often spring up without green space provision or energy-efficient design. Roads are expanded to accommodate private vehicles while public transport and cycling infrastructure receive limited investment. This trajectory deepens carbon dependency and undermines liveability. Sustainable Urban Development Theory challenges this model by advancing planning principles such as compact growth, mixed land use, transit-oriented development, and biophilic design. It stresses that sustainability is not a luxury reserved for wealthy nations but a necessity for rapidly growing cities in the Global South. Embedding sustainability at this stage of Benin’s growth is crucial to avoid locking the city into a high-carbon future (UN-Habitat, 2020 ). Within this study, the theory provides the “why” the normative justification for embedding carbon sequestration into every facility, from schools and hospitals to markets and drainage systems. 2.4 Synthesising the Frameworks Individually, UPE, the Circular Bioeconomy, and Sustainable Urban Development each illuminate vital aspects of urban carbon sequestration. UPE exposes the socio-political inequalities shaping environmental outcomes, reminding us that carbon strategies must be just. The Circular Bioeconomy operationalises this vision, providing mechanisms to transform linear, resource-depleting infrastructures into regenerative, carbon-storing systems. Sustainable Urban Development, in turn, anchors both within a long-term normative vision of balanced growth and climate-compatible cities. When synthesised, these frameworks generate a holistic analytical foundation. UPE demands attention to governance and justice, the Circular Bioeconomy explains how to operationalise carbon sequestration, and Sustainable Urban Development outlines why it must be embedded as a core principle. Together, they reinforce the central argument of this study: carbon sequestration is not an optional add-on but a transformative organising principle for urban planning in Benin Metropolis. See Fig. 1 for the interaction between the frameworks. 2.5 Relevance to Benin Metropolis For Benin Metropolis, these frameworks are especially pertinent. UPE reveals how governance fragmentation among local, state, and federal authorities constrains coherent planning. The Circular Bioeconomy resonates with the city’s strong informal economy and agricultural hinterland, offering strategies to align carbon sequestration with livelihoods and resource efficiency. Sustainable Urban Development underscores the urgency of embedding carbon-gaining practices now, before the city’s infrastructural trajectory becomes locked into unsustainable patterns. Crucially, situating these insights within the implementation of Nigeria’s Climate Change Act (2021) strengthens the relevance of this study. The Act sets a national mandate for emission reduction and climate resilience, but its success depends on local application. By linking UPE’s governance critique, the Circular Bioeconomy’s practical pathways, and Sustainable Urban Development’s normative principles, this framework shows how Benin Metropolis can translate national commitments into grounded, context-specific action. Taken together, the three frameworks illuminate both the barriers and opportunities facing Benin Metropolis. They affirm that transforming facilities into carbon sinks requires not only new technologies but also shifts in governance, cultural values, and economic systems. By grounding this study in UPE, the Circular Bioeconomy, and Sustainable Urban Development Theory, the analysis moves beyond technical prescriptions to a deeper understanding of the socio-ecological systems that will shape Benin Metropolis’s climate future. 3. Literature Review Over the past two decades, literature on urban carbon sequestration has expanded considerably, reflecting a growing awareness of the crucial role cities play in addressing climate change crisis. Research in this field generally clusters around three interconnected strategies: reducing emissions, enhancing carbon sinks, and reshaping governance systems. Bulk of this evidence, however, stems from Europe, North America, and Asia, where studies have demonstrated the technical feasibility and economic value of diverse interventions. In contrast, contributions from African contexts particularly sub-Saharan cities remain limited. This imbalance leaves an important gap for fast-growing cities like Benin, where rapid urbanisation and ecological degradation intersect. To address this, the present review draws on global, regional, and Nigerian literature across five thematic domains green infrastructure, sustainable building materials and design, transportation, waste and water management, and governance before identifying the gaps and opportunities most pertinent to Benin Metropolis. 3.1 Green Infrastructure Green infrastructure including urban forests, street trees, parks, wetlands, and green roofs has emerged as one of the most documented strategies for urban carbon sequestration. Scholars consistently emphasise that vegetation not only absorbs CO₂ but also generates co-benefits such as cooling, biodiversity conservation, stormwater regulation, and enhanced liveability (Gill et al., 2007 ; Nowak et al., 2013 ). For instance, Nowak et al. ( 2013 ) estimated that urban trees in the United States sequester approximately 22.8 million tonnes of carbon annually, while researches showed that European tree canopy cover can offset significant local emissions (European Forest Institute n.d.; Psistaki et al., 2024 ; Sicard et al., 2025 ). At the micro level, each urban tree can sequester 20–50 kg of CO₂ annually, while green roofs contribute between 0.5 and 2.5 kg CO₂ per square metre each year (Getter et al., 2009). In African cities, however, greening efforts encounter systemic challenges. Weak institutional frameworks, insecure land tenure, and limited maintenance capacity often undermine implementation (Cobbinah & Niminga-Beka, 2017 ). In Accra, rapid urban expansion has eroded green cover despite policies advocating tree planting (du Toit et al., 2018 ). Nigerian studies reveal similar tensions: while urban trees and parks offer potential for meaningful carbon storage, sustainability is jeopardised by vandalism, poor enforcement, and low public awareness (Alabi, 2020 ; Dipeolu, 2021 ; Adegun et al., 2021 ). For Benin Metropolis, located within a tropical forest zone yet experiencing rapid deforestation and land conversion, green infrastructure is particularly salient. The replacement of vegetation with asphalt has amplified heat and flood risks. Strategic initiatives such as community-led tree planting, integration of green roofs, and urban reforestation could both sequester carbon and improve liveability. Yet their success depends on tackling governance fragmentation, securing land tenure, and mobilising financial resources. Robust policy support, as well as community buy-in, will be indispensable for sustaining gains. 3.2 Carbon-Negative Building Materials and Design The construction sector is a global hotspot for emissions, accounting for nearly 40% of energy-related CO₂ emissions (IEA, 2021 ). Much of this stems from the embodied carbon of cement and steel. As a response, scholars and practitioners are exploring carbon-negative or low-carbon building materials. Churkina et al. ( 2020 ) argue that widespread adoption of mass timber construction could lock away carbon for decades, with models suggesting up to 20 gigatonnes of storage potential by 2050 if half of global new construction shifted to timber. Similarly, bamboo, hempcrete, and other bio-based alternatives provide promising pathways (Firoozi et al., 2024 ). Pilot projects in Europe and North America, particularly those deploying Cross-Laminated Timber (CLT), demonstrate reduced embodied energy, faster construction times, and long-term carbon storage (Ahmed & Arocho, 2020 ; Sherman & Fazeli, 2022 ). CLT has been shown to reduce embodied carbon by over 60% compared to conventional concrete and steel (Churkina et al., 2020 ). Green roofs further complement this by sequestering CO₂ while providing cooling benefits (Getter et al., 2009). In Nigeria, research into sustainable building practices is emerging. Oladokun and Akinola ( 2020 ) highlight bamboo and timber’s potential, but note challenges of quality assurance, cultural perceptions, and outdated codes. Chima ( 2025 ) emphasised the need for updated building regulations and investment in local supply chains that are eco-friendly. For Benin Metropolis, situated near resource-rich Edo forests, opportunities exist to develop localised timber-based construction systems. However, unchecked exploitation risks deforestation, highlighting the need for sustainable forestry management. Retrofitting older buildings with insulation, efficient lighting, and solar energy remains underexplored but offers parallel opportunities. 3.3 Transportation and Mobility Globally, transportation contributes about 24% of energy-related CO₂ emissions, with road vehicles as the dominant source (IEA, 2023). Research demonstrates the importance of promoting active mobility (cycling, walking), electrifying fleets, and expanding mass transit systems to reduce emissions and improve air quality (Creutzig et al., 2015). In African contexts, transport is dominated by informal minibuses, motorcycles, and ageing fleets with poor efficiency (Pirie, 2013 ). Innovations such as Lagos’ Bus Rapid Transit (BRT) showcase how investments in public transport can simultaneously cut emissions and reduce travel times (Oduwaye & Ede, 2021 ). Kigali’s electric motorcycle initiatives further highlight scalable low-carbon mobility (Uwase et al., 2022 ). Benin Metropolis mirrors these regional challenges: limited mass transit, growing private vehicle ownership, and rising congestion. Research indicates that electrifying buses, investing in cycling infrastructure, and redesigning road systems for mixed-use transport could substantially reduce emissions (Cai et al., 2024 ; Tozluoğlu et al., 2024 ). Such measures indirectly support carbon sequestration by cutting fossil fuel reliance. Importantly, mobility transitions require behavioural shifts supported by incentives, subsidies, and awareness campaigns. Without cultural acceptance and strong governance, adoption is likely to falter. 3.4 Waste and Water Management Waste and water infrastructure present both risks and opportunities. Globally, waste contributes about 5% of greenhouse gas emissions, particularly methane from landfills (UNEP, 2020 ). Conversely, strategies such as composting, anaerobic digestion, and bioenergy generation can divert organic waste into carbon-storing pathways (Bernstad & la Cour Jansen, 2012 ). Constructed wetlands, with sequestration potential of 100–200 g C per square metre annually, provide cost-effective solutions for wastewater treatment, flood control, and biodiversity conservation (Maucieri et al., 2017; Retta et al., 2023 ). In Nigeria, most cities including Benin struggle with open dumping, low recycling rates, and weak formal systems (Ike et al., 2018 ). Yet the informal sector plays a vital role in recycling plastics, metals, and organic waste. Formalising and supporting these actors could enhance both efficiency and equity. Decentralised composting hubs and small-scale biogas units align with Benin’s resource constraints and offer scalable solutions. Integrating wetlands into peri-urban zones could also enhance ecosystem services while supporting sequestration. 3.5 Community Engagement and Policy Frameworks Technical strategies alone cannot guarantee sustainability; social and institutional dynamics are equally crucial. Evidence suggests that community participation in greening, waste segregation, and mobility projects enhances ownership, reduces vandalism, and ensures long-term viability (Brown & Taylor, 2020; Paudel & States, 2023 ; Muhoza & Zhou, 2024 ; Kamana et al., 2024 ; Kochskämper et al., 2024 ). Community engagement builds resilience and social capital, both vital for adapting to climate change impacts. Policy and governance frameworks create the enabling conditions. Globally, instruments such as carbon pricing, green building codes, and mandatory urban greening drive substantial progress (OECD, 2021 ). In Nigeria, the 2021 Climate Change Act is a milestone, mandating carbon budgets and governance structures (Federal Government of Nigeria, 2021 ). Yet integration at the municipal level remains weak, with city plans rarely embedding carbon sequestration explicitly. For Benin Metropolis, aligning the Master Plan with carbon goals, reforming building codes, and strengthening participatory governance could unlock significant opportunities. Partnerships across government, private actors, and civil society will be critical to financing and scaling interventions. 3.6 Identified Gaps Despite progress in global scholarship, gaps remain highly relevant for Benin Metropolis. First, African contexts are underrepresented, with most empirical data drawn from developed regions. Second, interventions are often studied in isolation tree planting, waste, or mobility rather than integrated into cohesive frameworks. Third, socio-political dimensions of justice, equity, and governance remain underexplored, despite their critical importance. Finally, there is little empirical measurement of sequestration potential within Nigerian ecological contexts, hampering evidence-based policymaking. These gaps reinforce the significance of this study, which synthesises diverse global insights while contextualising them for Benin Metropolis. By drawing together strategies across green infrastructure, sustainable buildings, mobility, waste systems, and participatory governance, the research seeks to fill a crucial void in both academic discourse and urban planning practice. 4. Methodology The research adopted a systematic and comprehensive approach due to the dispersed and multidisciplinary nature of relevant studies spanning urban planning, geography, ecology, architecture, engineering, and the social sciences. A systematic review combined with meta-analysis was selected as the most suitable methodology. This dual design enabled the synthesis of diverse evidence, identification of recurring patterns, and generation of insights contextualised to Benin Metropolis, Nigeria. 4.1 Research Design The study employed a systematic review and meta-analytic framework guided by the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines (Page et al., 2021 ). Unlike traditional literature reviews, this approach follows a transparent, replicable process of identifying, screening, and synthesising studies. Where feasible, meta-analysis allowed for the aggregation of quantitative findings, such as the carbon sequestration potential of trees, green roofs, or mass timber. This design was chosen to capture both the breadth of available research and enable comparative evaluation, providing policymakers and planners with robust benchmarks. 4.2 Data Sources and Search Strategy To build a comprehensive evidence base, the study searched multiple academic databases, including Scopus, Web of Science, PubMed, Google Scholar, and JSTOR. Grey literature was also consulted, including reports from the Intergovernmental Panel on Climate Change, UN-Habitat, and Nigeria’s Federal Ministry of Environment. This ensured that both academic and policy-driven evidence were captured. Search terms were structured around urban planning, carbon sequestration, and facility-based interventions, using Boolean operators such as: (“urban planning” OR “urban facility” OR “infrastructure”) AND (“carbon sequestration” OR “carbon sink”) (“green infrastructure” OR “urban forest” OR “green roof”) AND (“climate mitigation” OR “carbon storage”) (“mass timber” OR “bio-based materials”) AND (“city” OR “urban”) (“waste management” OR “composting” OR “anaerobic digestion”) AND (“carbon sequestration” OR “greenhouse gases”) (“constructed wetlands” OR “wastewater treatment”) AND (“carbon storage” OR “emission reduction”) The review was limited to studies published between 2000 and 2025, reflecting the period of heightened global attention to climate change and the rise of sustainable urbanism. 4.3 Inclusion and Exclusion Criteria To ensure methodological rigour, inclusion criteria focused on peer-reviewed articles, book chapters, or credible institutional reports dealing specifically with carbon sequestration in urban contexts. Studies presenting empirical data quantitative or qualitative were prioritised, especially those addressing buildings, transport, waste, water systems, and green infrastructure. Only English-language publications were considered. Exclusion criteria ruled out studies focused exclusively on rural landscapes, forestry plantations, or large-scale geoengineering such as carbon capture and storage (CCS). Articles without empirical data, purely theoretical pieces, duplicates, and grey literature lacking transparency were also excluded. These criteria ensured that the reviewed evidence remained both relevant and robust. 4.4 Screening and Selection Process The search yielded about 1,500 records. After removing duplicates, 1,200 studies remained. Screening of titles and abstracts reduced this to 210, and full-text review against the criteria resulted in 60 studies being included in the qualitative synthesis and 40 in the meta-analysis. The PRISMA flow diagram (Fig. 2 ) documents each stage of identification, screening, eligibility, and inclusion, ensuring transparency and replicability. 4.5 Data Extraction and Analysis From each included study, variables such as intervention type (e.g., trees, mass timber, wetlands), geographic location, and carbon sequestration potential (e.g., CO₂ stored per year or embodied carbon avoided) were extracted. Co-benefits including cooling, flood control, biodiversity, and energy generation were noted alongside barriers and enabling factors such as governance, finance, and community engagement. Data were thematically coded into categories corresponding to urban facilities: green infrastructure, buildings, transport, waste, and water. Meta-analysis was used to calculate pooled effect sizes where comparable data existed (e.g., tree sequestration rates), while qualitative synthesis captured governance, policy, and social insights. 4.6 Validity and Reliability Measures To enhance reliability, multiple databases were searched, peer-reviewed and transparent studies were prioritised, and a standardised template guided data extraction. Triangulation was achieved by combining academic and grey literature. However, key limitations remain. The scarcity of empirical studies from African cities limited the strength of the meta-analysis for some interventions, and adapting global findings to Benin Metropolis required careful contextualisation. This challenge underscores the need for more localised research to strengthen the evidence base. 4.7 Justification for Methodological Approach The choice of a systematic review with meta-analysis was deliberate. Urban carbon sequestration remains a relatively new field, with evidence fragmented across disciplines and geographies. For policymakers in Benin Metropolis, fragmented insights are insufficient; what is required is a consolidated, evidence-based framework. This methodology enables such integration, offering both breadth and depth. The meta-analytic component provides quantitative benchmarks for example, the average annual carbon sequestration capacity of urban trees or the comparative efficiency of constructed wetlands. Meanwhile, the systematic review component illuminates governance and socio-political barriers, ensuring strategies are not only technically feasible but also socially and institutionally viable. 4.8 Relevance to Benin Metropolis Applying this methodology to Benin Metropolis is particularly valuable because the city lacks localised empirical research on carbon sequestration. By synthesising global lessons and adapting them to local realities, this study bridges a critical knowledge gap. The thematic synthesis offers a decision-making blueprint, helping policymakers evaluate which strategies community tree planting, mass timber construction, decentralised composting, or constructed wetlands are most viable within Benin’s ecological, economic, and governance conditions. Ultimately, this methodological design ensures that the recommendations produced are not mere imports of Western practices but a critically adapted framework tailored to the specific challenges and opportunities of an African city. It balances academic rigour with practical relevance, ensuring that findings can guide both scholarship and actionable policy in Benin Metropolis. 5. Results and Findings This study synthesised evidence from North America, Europe, Asia, and Africa to assess the feasibility of integrating carbon sequestration into urban facility planning. The findings confirmed that such integration is not only technically viable but also capable of delivering substantial environmental, social, and economic co-benefits. For Benin Metropolis, the strongest opportunities lie in expanding green infrastructure, adopting carbon-negative building design, advancing sustainable mobility, and deploying circular waste and water management systems. Collectively, these interventions offer a pathway for the city to transition from being a net carbon source to a carbon sink. 5.1 Green Infrastructure Facilities Across all facility categories, urban green infrastructure emerged as the most powerful contributor to carbon sequestration. Meta-analysis confirms that mature urban trees sequester between 20–50 kg of CO₂ per tree annually, depending on species, age, and climatic conditions (Nowak et al., 2013 ). Green roofs, while less impactful per unit, absorb 0.5–2.5 kg of CO₂ per square metre each year, and at scale provide meaningful gains (Getter & Rowe, 2006 ). Urban parks that integrate native tree species demonstrate long-term carbon storage advantages over ornamental landscapes (Strohbach & Haase, 2012 ). African evidence reveals significant challenges, particularly weak institutional frameworks that undermine tree planting initiatives (Cobbinah & Niminga-Beka, 2017 ). Nevertheless, successful case studies from Nairobi and Accra illustrate that community-driven greening, supported by strong stewardship, can deliver lasting benefits. For Benin Metropolis, interventions such as planting native, high-biomass species along streets and in parks, mandating street tree corridors, and incentivising rooftop greening could significantly boost sequestration while mitigating heat islands and flood risks. 5.2 Public Buildings and Carbon-Negative Materials Buildings represent another high-potential sector for carbon sequestration. Studies on mass timber and Cross-Laminated Timber (CLT) construction demonstrate reductions of over 60% in embodied carbon compared to conventional concrete and steel (Churkina et al., 2020 ). A CLT building can store between 500–700 kg of CO₂ per square metre of floor area, effectively locking carbon for the lifetime of the structure (Ahmed & Arocho, 2020 ; Sherman & Fazeli, 2022 ). Complementary strategies include integrating green roofs and bio-based insulation. Life cycle analyses show these measures not only offset embodied emissions but also enhance sequestration and cooling effects (Perini & Rosasco, 2016 ). In tropical contexts, bamboo, hempcrete, and other bio-based alternatives have demonstrated potential to reduce lifecycle emissions while supporting affordable housing (Firoozi et al., 2024 ). In Nigeria, however, adoption is hindered by cultural preferences for concrete, outdated building codes, and perceptions of timber as “inferior” (Oladokun & Akinola, 2020 ). For Benin Metropolis, proximity to forest resources in Edo State offers a unique opportunity to establish sustainable supply chains, provided governance mechanisms safeguard against overharvesting. Pilot projects, for example, constructing a public library or school using mass timber could demonstrate feasibility, update perceptions, and build confidence in carbon-negative building practices. 5.3 Transportation and Mobility Systems Transportation remains a dominant source of urban emissions. Globally, the sector accounts for about 24% of energy-related CO₂ emissions (IEA, 2023). The review shows that mass transit investment, active transport promotion, and vehicle electrification reduce emissions significantly. Electrifying bus fleets in Chinese and European cities cut emissions by 30–50%, depending on energy sources (Liu et al., 2019 ). Similarly, cycling networks and pedestrian infrastructure reduce short car trips, indirectly lowering carbon footprints (Creutzig et al., 2015). African experiences reinforce this potential. Lagos’ Bus Rapid Transit (BRT) system cut travel time by 40% and lowered corridor CO₂ emissions by 13% within five years (Oduwaye & Ede, 2021 ), while Kigali pioneered electric motorcycles as a scalable model of low-carbon mobility (Uwase et al., 2022 ). For Benin Metropolis, dominated by private cars, minibuses, and motorcycles, the most viable interventions include piloting electric buses, electrifying minibuses, and investing in safe pedestrian and cycling infrastructure. While transport does not directly sequester carbon, reducing reliance on fossil fuels substantially improves the city’s net carbon balance. 5.4 Waste and Water Management Facilities Waste management systems present both critical challenges and untapped opportunities. Globally, diverting organic waste from landfills through composting avoids emissions of approximately 0.27 tonnes of CO₂-equivalent methane per tonne of waste while adding about 0.1 tonnes of CO₂-equivalent to soils through carbon-rich compost (Bernstad & la Cour Jansen, 2012 ; Boldrin et al., 2009 ). Anaerobic digestion offers additional benefits by producing biogas that offsets fossil fuel use. Constructed wetlands provide complementary carbon gains, sequestering 100–200 grams of carbon per square metre annually while delivering water purification, stormwater management, and habitat creation (Retta et al., 2023 ; Brix & Arias, 2005 ). Case studies in Asia show wetlands to be cost-effective and resilient alternatives to energy-intensive wastewater treatment. In Nigeria, however, most cities including Benin rely on open dumping and poorly managed landfills, with limited composting infrastructure (Ike et al., 2018 ). The findings suggest that even decentralised composting units and small-scale biogas plants could dramatically reduce emissions while creating fertiliser, renewable energy, and green jobs. Integrating constructed wetlands into drainage and wastewater systems could further address Benin’s recurrent flooding while enhancing sequestration. 5.5 Community Engagement and Governance A consistent insight across facility types is the centrality of community participation. Evidence from Africa and beyond shows that tree planting, waste segregation, and neighbourhood greening initiatives succeed when communities are actively involved in design and maintenance (Paudel & States, 2023 ; Muhoza & Zhou, 2024 ). Policy frameworks are equally critical: supportive legislation, updated building codes, and participatory governance structures enable technical solutions to succeed (OECD, 2021 ; Federal Government of Nigeria, 2021 ). For Benin Metropolis, embedding carbon goals into the Master Plan, mandating waste segregation, and promoting public awareness campaigns will be vital. 5.6 Comparative Impact Assessment Comparing the carbon sequestration potential of different urban facilities is essential for identifying priority areas where interventions can yield the greatest environmental and socio-economic benefits. While each facility type green infrastructure, buildings, transport, waste, and water systems offers distinct pathways for reducing emissions or enhancing carbon sinks, their impacts vary significantly in scale, feasibility, and co-benefits. A comparative assessment provides clarity on which interventions hold the greatest promise for Benin Metropolis, were resource constraints and rapid urbanisation demand carefully targeted strategies. By weighing both direct carbon gains and indirect contributions such as cooling, flood control, and improved mobility, this assessment highlights not only the technical potential of each facility but also its contextual relevance. The synthesis of findings across facility types area summarised in the Table 1 . Table 1 Carbon Sequestration Potential by Facility Type Facility Type Intervention Estimated Carbon Impact Contextual Relevance to Benin Metropolis Source Green Infrastructure Trees, parks, green roofs 20–50kg CO₂/tree/year; 0.5–2.5kg CO₂/m²/year (roofs) High potential; limited by land competition and weak maintenance capacity Nowak et al. ( 2013 ); Getter & Rowe ( 2006 ); Strohbach & Haase ( 2012 ); Cobbinah & Niminga-Beka ( 2017 ); Orobator & Adahwara ( 2022 ); Dipeolu ( 2021 ) Buildings Mass timber, bio-based materials, retrofits 60%+ reduction in embodied carbon; 500–700kg CO₂/m² stored Strong potential given forest resources; requires policy reforms and updated codes Churkina et al. ( 2020 ); Ahmed & Arocho ( 2020 ); Sherman & Fazeli ( 2022 ); Perini & Rosasco ( 2016 ); Firoozi et al. ( 2024 ); Oladokun & Akinola ( 2020 ); Chima ( 2025 ) Transport EVs, mass transit, active transport 30–50% reduction in emissions (indirect effect) Feasible with pilot EV projects and improved public transit Liu et al. ( 2019 ); IEA (2023); Oduwaye & Ede ( 2021 ); Uwase et al. ( 2022 ); Cai et al. ( 2024 ); Tozluoğlu et al. ( 2024 ) Waste Facilities Composting, anaerobic digestion Avoids ~ 0.27 tCO₂e/tonne waste; adds ~ 0.1 tCO₂e to soils High potential due to heavy reliance on open dumping Bernstad & la Cour Jansen ( 2012 ); Boldrin et al. ( 2009 ); Ike et al. ( 2018 ) Water Facilities Constructed wetlands 100–200 g C/m²/year Relevant for flooding control and sanitation Retta et al. ( 2023 ); Brix & Arias ( 2005 ); Muhoza & Zhou ( 2024 ) Source: Author’s Compilation, 20205. Table 1 highlighted the comparative carbon sequestration potential of different urban facilities and their contextual relevance to Benin Metropolis. Green infrastructure comprising trees, parks, and green roofs shows strong capacity for both direct carbon capture and multiple co-benefits such as heat reduction and flood mitigation. Mature urban trees can sequester 20–50 kg of CO₂ annually, while green roofs contribute an additional 0.5–2.5 kg CO₂ per square metre per year. However, the potential of these interventions in Benin Metropolis is constrained by challenges such as competition for land, weak institutional frameworks, and poor maintenance culture, which limit sustainability despite high ecological benefits. In the building sector, interventions such as mass timber construction, bio-based materials, and retrofitting stand out for their ability to reduce embodied carbon by over 60%, with timber structures capable of storing 500–700 kg of CO₂ per square metre. This presents a particularly strong opportunity for Benin Metropolis given the availability of forest resources in Edo State. Nevertheless, outdated building codes, weak governance mechanisms, and societal perceptions of timber as inferior to concrete create significant barriers that must be addressed through reforms and awareness campaigns. Transportation facilities offer indirect sequestration benefits by reducing emissions through electrification, mass transit, and active mobility systems. The estimated 30–50% reduction in emissions underscores their importance for long-term decarbonisation. For Benin Metropolis, these interventions are feasible but would require investment in pilot electric vehicle fleets, expansion of public transit systems, and infrastructure for walking and cycling. Waste facilities emerge as one of the most immediately actionable areas for intervention. Composting and anaerobic digestion not only prevent the release of methane a highly potent greenhouse gas but also enhance soil carbon sequestration, avoiding about 0.27 tonnes of CO₂-equivalent per tonne of organic waste and adding approximately 0.1 tonnes to soils. Given Benin Metropolis’s reliance on open dumping, this pathway holds high potential for both climate and public health benefits. Finally, water facilities such as constructed wetlands demonstrate moderate but significant carbon sequestration capacity, storing 100–200 grams of carbon per square metre annually. Their relevance in Benin Metropolis lies not only in carbon capture but also in their ability to address flooding and sanitation challenges, which are pressing urban issues. See Fig. 3 for the Comparative Carbon Sequestration Potential by Facilities Type in Benin Metropolis. The results from Fig. 3 showed a striking disparity between categories, highlighting the relative magnitude of each intervention’s impact. Buildings stand out as the most impactful sector, with an estimated sequestration or emission reduction potential of about 600 scaled units. This dominance reflects the substantial benefits of adopting mass timber construction, retrofits, and bio-based materials, which can lock carbon in structural components while simultaneously reducing embodied emissions. In contrast, transport (40) and green infrastructure (35) each demonstrated a more modest but still a meaningful contribution, averaging around 40 scaled units. In green infrastructure, urban trees, parks, and green roofs sequester carbon directly while offering critical co-benefits such as urban cooling, flood control, and biodiversity enhancement. Transport interventions, on the other hand, primarily reduce emissions indirectly through electrification, mass transit, and active mobility systems. Their relatively similar contribution to green infrastructure highlights the shared role of both sectors as medium-impact strategies that require supportive policies and investment for effective implementation. Waste and water facilities rank the lowest in terms of direct carbon sequestration potential, with 0.27 and 0.15 scaled units respectively. Despite their smaller numerical contribution, these interventions should not be underestimated. Composting, anaerobic digestion, and constructed wetlands not only provide carbon benefits but also address urgent challenges in Benin Metropolis such as poor sanitation, flooding, and methane emissions from unmanaged waste. Their value lies in multifunctionality delivering ecosystem and health benefits alongside modest carbon gains. Hence, Fig. 3 highlighted a critical insight: while buildings offer the greatest single opportunity for carbon sequestration, Benin Metropolis cannot rely on one facility type alone. Instead, a diversified strategy is needed, where green infrastructure, transport, and waste-water systems complement building interventions. Together, these pathways form an integrated framework that balances high carbon storage with immediate co-benefits for urban resilience and sustainability. 5.7 Key Cross-Cutting Findings Several broader insights emerged: first, interventions that generate immediate co-benefits such as reduced flooding, heat mitigation, and improved sanitation are more likely to gain traction. Second, socio-institutional barriers, including governance fragmentation, financing gaps, and limited technical expertise, outweigh technical challenges in constraining implementation. Third, sustained community engagement is indispensable to ensure long-term maintenance and acceptance. Finally, medium-sized cities like Benin, while resource-constrained, retain flexibility to experiment and innovate since they are less entrenched in carbon-heavy infrastructures. 5.8 Implications for Benin Metropolis For Benin Metropolis, the findings underscore that green infrastructure and decentralised waste management represent the most immediately actionable strategies, combining strong sequestration potential with urgent co-benefits. Mass timber and other bio-based building strategies hold medium- to long-term promise but will require regulatory reforms, investment in local supply chains, and cultural acceptance. Transport interventions, particularly electrification and transit upgrades, are essential to curb future emissions. Constructed wetlands offer a multifunctional solution, addressing flooding and sanitation while providing modest sequestration benefits. Taken together, the results provide a robust empirical foundation for the integrative framework developed in later sections. They demonstrate that transforming Benin Metropolis’s facilities into carbon sinks is feasible, but success will depend on governance reforms, community participation, and long-term policy commitment. 6. Discussion of Results The results of this study revealed that integrating carbon sequestration into urban facility planning is both feasible and potentially transformative for metropolitan area like Benin. The findings revealed that interventions such as urban greening, carbon-negative construction, sustainable transportation, waste-to-resource systems, and constructed wetlands are effective in reducing emissions and enhancing carbon sinks. Yet, the deeper significance of these findings emerges when they are interpreted through the lenses of Urban Political Ecology (UPE), the Circular Bioeconomy, and Sustainable Urban Development Theory . The discussion that follows critically situates the findings within these theoretical frames, while also considering practical challenges, governance dynamics, and the lived realities of Benin Metropolis. 6.1 Linking Results to Urban Political Ecology Urban Political Ecology highlights how power, inequality, and governance shape environmental outcomes. The findings confirm that socio-political barriers, more than technological constraints, determine the success of carbon sequestration strategies. For example, while green infrastructure has clear carbon and co-benefits, its deployment in Benin Metropolis is hampered by competing land uses, weak enforcement of planning laws, and limited budget allocations. These challenges reflect deeper political choices about what is prioritised in urban development: short-term revenue from real estate expansion versus long-term ecological sustainability. Similarly, waste management in Benin Metropolis illustrates UPE’s claim that environmental crises are socially produced. The reliance on open dumps is not inevitable but results from governance failures, insufficient investment, and marginalisation of informal recyclers. The findings that decentralised composting and anaerobic digestion could cut emissions highlight the lost opportunities embedded in current power arrangements. Unless the city deliberately integrates informal actors into formal systems, carbon-saving strategies risk reproducing inequalities by excluding those who already contribute to recycling under precarious conditions. In transport, UPE underscores that transitions to electric mobility are not simply technical shifts but political-economic projects requiring subsidies, infrastructure, and regulatory reform. If poorly managed, they could widen inequalities benefiting wealthier commuters who can afford electric cars while leaving poorer residents reliant on polluting minibuses. Thus, the results confirm that carbon gains in Benin Metropolis must be evaluated through questions of justice: Who benefits? Who pays? Who is left behind? 6.2 Interpreting Results through the Circular Bioeconomy The Circular Bioeconomy provides a complementary lens, focusing on efficiency and regeneration. The findings strongly resonate with this paradigm. Waste facilities, for instance, illustrate how organic matter can be transformed from a methane source into a carbon sink and resource for compost or energy. Similarly, the adoption of mass timber and bamboo aligns with the circular principle of substituting finite, carbon-intensive materials with renewable, carbon-storing ones. The results also underscore the importance of local resource cycles. Edo State’s forests present opportunities for a timber-based construction economy, but only if harvesting is managed sustainably. Without strong regulatory oversight, the risk of deforestation could outweigh carbon benefits. This reflects a central tension in the bioeconomy: balancing utilisation with regeneration. For Benin Metropolis, this means designing closed-loop systems where waste is recycled locally, water is purified through wetlands, and building materials are sourced responsibly. Crucially, the circular bioeconomy reframes sustainability as an opportunity rather than a burden. By showing that compost can improve soils, biogas can provide affordable energy, and timber construction can create jobs, the findings position carbon sequestration as a driver of green livelihoods. This perspective is particularly important in Nigeria, where unemployment and poverty remain pressing challenges. 6.3 Situating Results in Sustainable Urban Development Theory The third theoretical pillar, Sustainable Urban Development Theory, provides the normative foundation for interpreting results. The findings affirm that sustainability is not a luxury but a necessity. Benin Metropolis’s unplanned growth has already exacerbated flooding, heat stress, and waste crises. The evidence that constructed wetlands and urban forests can mitigate these risks demonstrates that carbon sequestration strategies are simultaneously adaptation and mitigation measures. Sustainable urbanism also highlights the importance of long-term integration. The results indicate that while transport electrification and timber construction require significant upfront investment, their long-term benefits justify inclusion in planning frameworks. Cities that fail to embed such strategies early risk being locked into carbon-intensive trajectories. For Benin, the urgency is clear: with its population projected to expand, the choices made now will determine whether it becomes a sustainable, carbon-conscious city or entrenches unsustainable growth. 6.4 Governance and Institutional Implications A cross-cutting theme in the findings is the centrality of governance. Whether in tree planting, building codes, or waste management, institutional weakness undermines implementation. For instance, evidence from Accra and Nairobi shows that tree planting initiatives often fail due to lack of maintenance. Benin risks repeating these failures unless governance structures ensure continuity. The findings also highlight opportunities for decentralised governance. Community-driven projects such as neighbourhood composting or local greening tend to be more sustainable than top-down initiatives. This suggests that Benin should adopt a multi-level governance model, combining state-level policy with community empowerment. International experience shows that polycentric governance, where multiple actors share responsibility, fosters innovation and accountability (Ostrom, 2010 ). 6.5 Social Justice and Equity Considerations The results raise critical issues of equity. Urban Political Ecology reminds us that carbon sequestration projects can inadvertently reproduce exclusion. For example, creating new parks or wetlands could displace informal settlers. Electrification of transport may privilege wealthier groups. Even tree planting may reinforce inequalities if maintenance is left to communities lacking resources. Therefore, strategies must be designed inclusively. Evidence from African cities shows that when communities are engaged in co-designing and co-managing facilities, projects achieve greater legitimacy and durability. For Benin, this means integrating informal waste pickers, market women, and neighbourhood associations into planning processes. Without such inclusion, carbon sequestration risks becoming another elite-driven agenda disconnected from urban realities. 6.6 Lessons from Global and Regional Comparisons The comparative evidence provides several lessons for Benin Metropolis. From Europe and North America, the adoption of mass timber shows the feasibility of scaling carbon-storing buildings, but it also highlights the need for updated codes and training. From Asian cities, constructed wetlands demonstrate cost-effective water management solutions suitable for tropical climates. From Lagos, the BRT system underscores the importance of investing in mass transit even amid governance challenges. From Kigali, electric motorcycles show that innovation is possible even in resource-constrained contexts. At the same time, the African cases caution against overreliance on imported models. Projects must be tailored to local realities. For instance, Benin cannot simply replicate Lagos’ BRT without addressing its different urban morphology and population density. Instead, the lesson is to adapt principles—mass transit, electrification, green spaces into context-specific designs. 6.7 Practical Implications for Benin Metropolis For Benin Metropolis, the findings suggest a hierarchy of priorities. Green infrastructure and waste management should be immediate priorities, as they deliver both carbon and urgent co-benefits such as flood control and sanitation. Transport and building reforms represent medium- to long-term goals requiring policy shifts and investments. Constructed wetlands can be integrated into ongoing drainage projects, providing a cost-effective dual solution. These priorities align with Nigeria’s Climate Change Act (2021), which mandates carbon budgeting. By embedding sequestration into the city’s Master Plan, Benin can position itself as a pioneer among Nigerian cities in operationalising the Act at a subnational level. Partnerships with universities, civil society, and international donors can provide technical and financial support. 6.8 The Human Dimension: Why This Matters Beyond technical details, the findings speak to a deeper human story. Benin Metropolis is already experiencing the brunt of climate change flooded streets, unbearable heat, unmanaged waste. These realities affect livelihoods, health, and dignity. The evidence that trees can cool neighbourhoods, compost can improve soils, and wetlands can reduce flooding is not abstract; it is about making the city more liveable for its people. Carbon sequestration, therefore, should not be seen as a distant global agenda but as a local pathway to restoring balance between people and their environment. This human dimension gives the findings moral urgency: the future of Benin depends not just on emission reductions but on re-imagining the city as a living carbon sink that sustains both people and planet. 6.9 Summary of Key Insights Carbon sequestration is technically feasible across multiple facility types in Benin Metropolis. The main obstacles are governance, institutional capacity, and social inclusion, rather than technology. Green infrastructure and waste management offer the most immediate gains; transport and buildings provide medium- to long-term opportunities. Success requires integration of technical, political, and social dimensions, consistent with the study’s theoretical framework. The ultimate significance lies in the human benefits—cooler, cleaner, healthier, and more resilient urban spaces. 7. Policy Implications The findings of this study underscore that the integration of carbon sequestration into urban facility planning is both urgent and feasible for Benin Metropolis. Yet, translating these opportunities into real outcomes requires deliberate policy interventions. The following section outlines the policy implications at the l ocal, state, national, and international levels , drawing connections between technical strategies, governance reforms, and broader development agendas. 7.1 Embedding Carbon Sequestration into Urban Planning Frameworks The most immediate implication is the need to embed carbon sequestration into Benin Metropolis’s Master Plan and related urban development policies. At present, most Nigerian urban plans prioritise housing, transport, and economic growth without explicitly addressing carbon sinks. This omission risks locking the city into unsustainable trajectories. Integrating carbon goals requires mandating green infrastructure corridors, tree-lined streets, wetlands in flood-prone areas, and the use of carbon-negative materials in public projects. Such integration should not be symbolic. Planning codes must include measurable carbon targets, ensuring that every new facility contributes to climate mitigation. For example, planning approvals could require developers to demonstrate how buildings or estates will sequester or offset carbon, whether through green roofs, bio-based construction, or urban forestry contributions. By embedding sequestration into the regulatory DNA of planning, Benin can institutionalise sustainability rather than treating it as an afterthought. 7.2 Updating Building Codes and Standards The findings show that mass timber, bamboo, and other bio-based materials significantly reduce embodied carbon. However, outdated building codes in Nigeria often restrict their use. A key policy implication is therefore the urgent revision of building codes to recognise and regulate carbon-negative materials. This should be accompanied by training programmes for architects, engineers, and builders to build technical capacity and public confidence. Government-led demonstration projects such as constructing schools, health centres, or administrative buildings with mass timber could serve as proof of concept, shifting cultural perceptions of timber as “inferior” to concrete. Edo State, with its timber resources, could lead this transition, provided sustainable forest management policies prevent overharvesting. 7.3 Strengthening Waste Management Policies The results revealed that waste management offers one of the most immediate carbon-saving opportunities. Yet, Benin Metropolis currently relies on open dumping, with minimal waste segregation. Policy implications include: Mandatory waste segregation at source for households, markets, and institutions, supported by public awareness campaigns. Decentralised composting and biogas plants integrated into neighbourhoods, turning organic waste into resources. Formal recognition of informal waste pickers , offering them training, protective equipment, and integration into municipal waste systems. Incentives for recycling industries , including tax breaks and access to microfinance. By shifting from a disposal mindset to a resource recovery model, Benin can cut methane emissions, enhance soil carbon, and create green jobs, aligning with circular bioeconomy principles. 7.4 Advancing Sustainable Mobility Policies Transport policies are critical to reducing Benin Metropolis’s emissions. The results suggest that electrifying minibuses and introducing mass transit could drastically reduce reliance on fossil fuels. Policy implications include: Establishing an Electric Vehicle (EV) Roadmap for the city, starting with pilot fleets of electric buses or minibuses. Providing charging infrastructure at key transport hubs. Offering tax incentives or subsidies for private adoption of electric motorcycles and cars. Expanding non-motorised transport infrastructure , including sidewalks and cycling lanes, to encourage behavioural shifts. These policies should be phased to match the city’s resource capacity, beginning with pilot projects before scaling citywide. Importantly, they must be designed inclusively to avoid privileging elites while leaving the majority reliant on polluting systems. 7.5 Integrating Constructed Wetlands into Drainage Policy Flooding is a recurrent problem in Benin Metropolis, exacerbated by climate change and unregulated construction. The results highlight constructed wetlands as cost-effective facilities that sequester carbon while improving drainage and water quality. Policy implications include mandating wetlands in new drainage and wastewater projects, particularly in flood-prone areas such as Upper Sakponba and Ugbowo. Such wetlands should be protected through zoning policies that prevent encroachment. Partnerships with universities and NGOs could ensure scientific monitoring, while community groups could be engaged for maintenance. This dual approach technical and social would ensure wetlands function as resilient, carbon-storing infrastructure. 7.6 Financing Carbon-Sequestering Infrastructure Financing emerged as a recurring challenge in the results. Many interventions require upfront investment even if they produce long-term savings. Policy responses must therefore mobilise diverse funding sources: Climate Finance : Benin Metropolis can access international funds such as the Green Climate Fund and the Global Environment Facility by aligning projects with Nigeria’s Nationally Determined Contributions (NDCs). Public-Private Partnerships (PPPs) : Private developers can be incentivised to invest in green infrastructure through land concessions, tax breaks, or co-financing schemes. Carbon Markets : By quantifying and verifying carbon gains, Benin could participate in voluntary carbon markets, generating revenue from sequestration projects. Local Green Bonds : Edo State could issue municipal green bonds to finance carbon-sequestering projects, tapping into domestic investors seeking sustainable portfolios. Without innovative financing mechanisms, even the most technically sound policies will remain aspirational. 7.7 Institutional and Governance Reforms The results emphasised governance fragmentation as a major barrier. Policy implications include clarifying institutional mandates for carbon governance. Currently, responsibilities are dispersed across ministries and agencies, leading to duplication or neglect. Benin Metropolis would benefit from establishing a Climate and Carbon Office within the local government, tasked with coordinating sequestration initiatives, monitoring carbon budgets, and liaising with state and federal agencies. Furthermore, polycentric governance where state, local, and community actors share responsibility should be institutionalised. For example, while the local government could oversee citywide planning, neighbourhood associations could manage local greening and composting projects. Such shared governance increases accountability and resilience. 7.8 Community Participation as Policy Priority The results showed that projects thrive when communities are actively engaged. Policy must therefore institutionalise participation. This could involve: Establishing neighbourhood green committees responsible for local tree planting and park maintenance. Providing micro-grants for community-led composting or wetland projects. Including informal workers in official waste and recycling systems. Embedding participatory budgeting, allowing communities to allocate part of the climate budget to local priorities. By grounding policies in community agency, carbon sequestration becomes not an imposed agenda but a shared responsibility. 7.9 Alignment with National and Global Agendas Local policies must align with broader frameworks. Nigeria’s Climate Change Act (2021) requires carbon budgeting and mainstreaming climate action across sectors. Benin Metropolis can operationalise the Act at the municipal level, setting a precedent for other Nigerian cities. Policies should also align with Sustainable Development Goal 11 (Sustainable Cities and Communities) and SDG 13 (Climate Action) , ensuring coherence with international commitments. At the global level, demonstrating progress could attract international partnerships and financing. Benin’s integration of carbon sequestration into urban facilities would not only meet local needs but also contribute to Nigeria’s NDCs under the Paris Agreement. 7.10 Risks of Inaction Finally, the policy implications are sharpened when contrasted with the risks of inaction. Without embedding carbon sequestration into planning, Benin Metropolis faces worsening floods, heat stress, air pollution, and waste crises. These risks carry significant economic costs in lost productivity, damaged infrastructure, and healthcare burdens. Conversely, proactive policies can transform these risks into opportunities—creating jobs, improving health, and enhancing resilience while contributing to global climate goals. 7.11 Summary of Policy Pathways The discussion above can be summarised into five policy pathways for Benin Metropolis: Institutionalising carbon goals in urban planning and building codes. Reforming waste and water systems into circular, carbon-sequestering infrastructures. Promoting sustainable transport , beginning with pilots in electrification and non-motorised mobility. Mobilising finance through climate funds, PPPs, carbon markets, and green bonds. Strengthening governance and participation , ensuring inclusive and accountable implementation. 8. Recommendations To operationalise the findings of this study, it is essential that carbon sequestration be embedded into the very foundations of urban planning in Benin Metropolis. The city’s Master Plan should be updated to include explicit carbon targets, ensuring that every new development contributes to climate mitigation. Developers ought to be required to integrate sequestration measures such as tree planting, green roofs, or the use of bio-based construction materials into their projects. Such policy adjustments will institutionalise sustainability, making it a standard rather than an exception. Reforming building codes is another priority. Nigeria’s existing codes largely restrict the use of mass timber, bamboo, and other carbon-negative materials, thereby reinforcing dependence on carbon-intensive concrete and steel. Revising these codes to recognise sustainable alternatives, alongside government-led demonstration projects, would showcase the viability and attractiveness of timber and bamboo buildings. This would not only reduce embodied carbon but also shift public perceptions of these materials from “inferior” to modern, durable, and climate-friendly solutions. Waste management also requires urgent transformation. Policies mandating household and institutional waste segregation should be introduced and supported by citywide awareness campaigns. Decentralised composting centres and anaerobic digestion facilities can convert organic waste into useful products such as compost and biogas, cutting methane emissions while creating livelihoods. Crucially, informal waste workers, who already play a central role in recycling, must be formally recognised and integrated into the municipal system, with training, equipment, and fair compensation provided to enhance their contributions. In the transport sector, a phased transition to low-carbon systems should be pursued. Pilot projects introducing electric minibuses, coupled with the development of charging infrastructure at transport hubs, would mark a significant step toward decarbonisation. At the same time, expanding pedestrian walkways and cycling lanes will make non-motorised mobility safer and more attractive, reducing short car trips. Policies should also provide subsidies or incentives for the gradual adoption of electric motorcycles, which are already popular in Benin Metropolis and could serve as an entry point for wider electrification. Water management must equally be reconceptualised. Constructed wetlands should be integrated into flood-prone zones as part of both drainage and wastewater systems. Beyond carbon sequestration, such wetlands would alleviate flooding, purify water, and create biodiversity corridors. Strong zoning policies will be required to protect these wetlands from encroachment, while community groups could be engaged in their upkeep to ensure long-term functionality and ownership. None of these interventions will be possible without financing and governance reforms. Benin Metropolis should actively pursue international climate finance opportunities, particularly through alignment with Nigeria’s Climate Change Act and its commitments under the Paris Agreement. Local financing options such as municipal green bonds and public–private partnerships must also be explored to mobilise resources. To coordinate efforts, a Climate and Carbon Office within the city government should be established, tasked with monitoring progress, enforcing carbon targets, and fostering collaboration across sectors. Finally, policies must prioritise community engagement. Urban residents are not passive beneficiaries but active stakeholders whose participation is essential for success. Participatory planning and budgeting should be institutionalised, enabling residents to shape local greening, composting, and wetland projects. Micro-grants for neighbourhood associations can stimulate grassroots innovation, while recognition of informal actors ensures inclusivity. By embedding participation at every stage, carbon sequestration will not only mitigate climate change but also strengthen trust, ownership, and collective responsibility across the city. 9. Final Reflection The evidence makes it clear that carbon sequestration in Benin Metropolis is not an abstract, distant goal but an urgent and achievable pathway to sustainability. Trees, timber, compost, wetlands, and electric mobility are not simply technical solutions; they are tools for reimagining the city as a place that restores rather than depletes. The challenge is not whether Benin can do this, but whether the political will, institutional reforms, and community partnerships can be mobilised quickly enough. If pursued decisively, the metropolitan area could emerge as a model for medium-sized African cities grappling with climate change. By embedding carbon sequestration at the heart of its planning agenda, Benin Metropolis has the chance to create not just a more sustainable urban environment but a more just, liveable, and resilient home for its people. 10. Conclusion This study has demonstrated the significant potential of embedding carbon sequestration into the planning and management of urban facilities in Benin Metropolis, Nigeria. Drawing on a systematic review and meta-analysis of global, regional, and Nigerian evidence, it showed that facilities such as green infrastructure, buildings, transport, waste systems, and constructed wetlands can be reimagined to operate not only as service providers but also as active carbon sinks. The comparative impact assessment (Table 1 and Fig. 3 ) revealed that green infrastructure and building rank as the most immediately actionable interventions, offering relatively low-cost, socially inclusive solutions with urgent co-benefits such as reduced flooding, improved sanitation, and enhanced thermal comfort. In contrast, waste management and transport systems hold strong medium- to long-term potential, particularly through mass timber, bio-based materials, and electrified mass transit, though these require significant policy reforms and infrastructural investment. Constructed wetlands , while modest in direct carbon gains, provide multifunctional benefits, particularly in flood management and sanitation, making them vital supporting interventions. Theoretically, the study advances a triadic framework combining Urban Political Ecology, the Circular Bioeconomy, and Sustainable Urban Development Theory. This synthesis underscores that carbon sequestration is not a purely technical matter but a multidimensional urban project. It involves addressing socio-political questions of governance and justice, operationalising regenerative material and ecological cycles, and embedding sustainability principles into long-term urban growth trajectories. For Benin Metropolis, the findings highlight both opportunity and challenge. The city’s ecological endowment, its proximity to Edo State’s forests, and its dynamic population growth provide fertile ground for innovation. Yet persistent governance weaknesses, fragmented planning, and limited financial capacity remain critical barriers. To address these, a staged approach is essential: Short-term (0–5 years) Prioritise community-driven tree planting, reforestation of degraded areas, decentralised composting, and pilot waste-to-energy initiatives. Medium-term (5–15 years) Integrate mass timber and bio-based materials into public building projects, establish electric bus pilots, and adopt policies incentivising green roofs and active transport infrastructure. Long-term (15 + years) Mainstream constructed wetlands into the city’s water and flood management systems, scale up sustainable building supply chains, and embed carbon sequestration principles into the city’s master planning and land-use frameworks. Generally, carbon sequestration must move from the margins to the centre of urban policy and facility planning in Benin Metropolis. By positioning it as a core organising principle, the city can simultaneously confront climate change, address socio-economic inequalities, and strengthen resilience against environmental risks. Conversely, failure to adopt this integrated, staged approach risks deepening ecological degradation and exacerbating urban challenges. Declarations Consent to Publish Declaration Not Applicable Consent to Participate Declaration Not Applicable Ethics Declaration Not Applicable Clinical Trial Number Not Applicable Data Availability Statement Not Applicable Clinical Trial Number Not Applicable References Adebayo A, Omoniyi S. Urban green spaces and climate change mitigation in Nigeria: Potentials and challenges. J Environ Planning Manage. 2019;62(5):785–803. https://doi.org/10.1080/09640568.2018.1470962 . Adegun OB, Ikudayisi EA, Morakinyo TE. Urban green infrastructure in Nigeria: A review. Sci Afr. 2021;14:e01044. https://doi.org/10.1016/j.sciaf.2021.e01044 . Ahmed S, Arocho I. Mass timber building material in the U.S. construction industry: Determining the existing awareness level, construction-related challenges, and recommendations to increase its current acceptance level. Clean Eng Technol. 2020;1:100007. https://doi.org/10.1016/S2666790820300070 . Alabi MO. Sustainable urban form and challenges of open space utilization, Akure, Nigeria as a case study. Int J Urban Sustainable Dev. 2020;12(1). https://doi.org/10.1080/19463138.2020.1728691 . Atedhor GO. Nigeria’s climate responsiveness: Navigating energy-climate and techno-financial conundrums in the low-carbon energy transition. Energy Sustain Dev. 2025;88:101810. https://doi.org/10.1016/j.esd.2025.101810 . Baró F, Chaparro L, Gómez-Baggethun E, Langemeyer J, Nowak DJ, Terradas J. Contribution of ecosystem services to air quality and climate change mitigation policies: The case of urban forests in Barcelona, Spain. Ambio. 2014;43(4):466–79. https://doi.org/10.1007/s13280-014-0507-x . Bernstad A, la Cour Jansen J. Review of comparative LCAs of food waste management systems: Current status and potential improvements. Waste Manag. 2012;32(12):2439–55. https://doi.org/10.1016/j.wasman.2012.07.023 . Boldrin A, Andersen JK, Møller J, Christensen TH, Favoino E. Composting and compost utilization: Accounting of greenhouse gases and global warming contributions. Waste Manage Res. 2009;27(8):800–12. https://doi.org/10.1177/0734242X09345275 . Brix H, Arias CA. The use of vertical flow constructed wetlands for on-site treatment of domestic wastewater: New Danish guidelines. Ecol Eng. 2005;25(5):491–500. https://doi.org/10.1016/j.ecoleng.2005.07.009 . Cai J, Zhao Z, Zhou Z, Wang Y. Predicting the carbon emission reduction potential of shared electric bicycle travel. Transp Res Part D: Transp Environ. 2024;129:104107. https://doi.org/10.1016/j.trd.2024.104107 . Campbell S. Green cities, growing cities, just cities? Urban planning and the contradictions of sustainable development. J Am Plann Association. 1996;62(3):296–312. https://doi.org/10.1080/01944369608975696 . Cervero R. (2000). Informal Transport in the Developing World . UN-Habitat. https://unhabitat.org/sites/default/files/download-manager-files/Informal%20Transport%20in%20the%20Developing%20World.pdf Chima WO. Innovative approaches to sustainable building practices in Nigeria: Advancing green construction through local materials and technological integration: A case study of Abuja Municipal Area Council (AMAC). Int J Latest Technol Eng Manage Appl Sci. 2025;14(6):783–90. https://doi.org/10.51583/IJLTEMAS.2025.140600085 . Churkina G, Organschi A, Reyer CPO, Ruff A, Vinke K, Liu Z, Reck BK, Graedel TE, Schellnhuber HJ. Buildings as a global carbon sink. Nat Sustain. 2020;3(4):269–76. https://doi.org/10.1038/s41893-019-0462-4 . Cobbinah PB, Niminga-Beka R. Urban planning and climate change in Africa: Experiences from Ghana. Habitat Int. 2017;69:49–58. https://doi.org/10.1016/j.habitatint.2017.09.009 . Creutzig F, Jochem P, Edelenbosch OY, Mattauch L, van Vuuren DP, McCollum D, Minx J, Transport. A roadblock to climate change mitigation? Science, 350 (6263), 911–2. https://www.science.org/doi/ 10.1126/science.aac8033 Dipeolu AA. Determinants of residents’ preferences for urban green infrastructures. Urban Forestry Urban Green. 2021;60., Article 127072. https://doi.org/10.1016/j.ufug.2020.127072 . du Toit MJ, Cilliers SS, Dallimer M, Goddard M, Guenat S, Cornelius SF. Urban green infrastructure and ecosystem services in sub-Saharan Africa. Landsc Urban Plann. 2018;180:249–61. https://doi.org/10.1016/j.landurbplan.2018.06.001 . Egharevba JO. (2025). From traditional to smart: Embedding human-centric principles into urban facility planning for inclusive development in African Cities. J Urban Dev Manage. Egharevba JO, Onaiwu DN. Economic impact of solid waste on the livelihood of scavengers in Benin City, Nigeria. Kad J Geogr. 2020;2(2):26–52. European Forest Institute (n. d.). ForestQuestions Q9: How will climate change affect forests and what can we do about it? Retrieved from https://efi.int/forestquestions/q9 Federal Government of Nigeria. Climate Change Act 2021. Federal Government; 2021. Firoozi AA, Firoozi AA, Oyejobi DO, Avudaiappan S, Saavedra Flores E. Emerging trends in sustainable building materials: Technological innovations, enhanced performance, and future directions. Results Eng. 2024;24:103521. https://doi.org/10.1016/j.rineng.2024.103521 . Getter KL, Rowe DB. The role of extensive green roofs in sustainable development. HortScience. 2006;41(5):1276–85. https://doi.org/10.21273/HORTSCI.41.5.1276 . Gill SE, Handley JF, Ennos AR, Pauleit S. Adapting cities for climate change: The role of the green infrastructure. Built Environ. 2007;33(1):115–33. https://doi.org/10.2148/benv.33.1.115 . Heynen N, Kaika M, Swyngedouw E. In the nature of cities: Urban political ecology and the politics of urban metabolism. Routledge; 2006. IEA. (2021). Global status report for buildings and construction 2021. Int Energy Agency. https://globalabc.org/sites/default/files/2021-10/GABC_Buildings-GSR-2021_BOOK.pdf Ike C, Ezeibe C, Anijiofor-Ike CS, Daud NNN. (2018). Solid waste management in Nigeria: Problems, prospects, and policies. The Journal of Solid Waste Technology and Management , 44(2), 163–172. https://doi.org/10.5276/JSWTM.2018.163 Intergovernmental Panel on Climate Change. (2022). Climate Change 2022: Impacts, Adaptation and Vulnerability (Working Group II contribution to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change) . https://www.ipcc.ch/report/ar6/wg2/ International Energy Agency. (2023, March 2). CO₂ Emissions in 2022: Growth in emissions lower than feared . IEA. https://iea.blob.core.windows.net/assets/3c8fa115-35c4-4474-b237-1b00424c8844/CO2Emissionsin2022.pdf Jiboye AD, Adebayo JA, Obakin OA. Urban housing in Nigeria for sustainable development: Challenges and prospects. Int J Adv Eng Res Sci. 2020;7(7):478–91. https://doi.org/10.22161/ijaers.77.55 . Kamana A, Radoine H, Nyasulu C. Urban challenges and strategies in African cities: A systematic literature review. City Environ Interact. 2024;21. https://doi.org/10.1016/j.cacint.2023.100132 . 100132, ISSN 2590 – 2520. Kochskämper E, Glass LM, Haupt W, Malekpour S, Grainger-Brown J. Resilience and the Sustainable Development Goals: a scrutiny of urban strategies in the 100 Resilient Cities initiative. J Environ Planning Manage. 2024;68(7):1691–717. https://doi.org/10.1080/09640568.2023.2297648 . Korhonen J, Honkasalo A, Seppälä J. Circular economy: The concept and its limitations. Ecol Econ. 2018;143:37–46. https://doi.org/10.1016/j.ecolecon.2017.06.041 . Liu Z, Wu Q, Wang S, Wei W, Xu G. The impact of electric buses on urban air quality and CO₂ emissions. Transp Res Part D: Transp Environ. 2019;75:31–45. https://doi.org/10.1016/j.trd.2019.07.006 . Muhoza JP, Zhou W. Urban Green Spaces in Africa: A Bibliometric Analysis. Environments. 2024;11(4):68. https://doi.org/10.3390/environments11040068 . National Assembly of the Federal Republic of Nigeria. (2021). Climate Change Act 2021 . https://faolex.fao.org/docs/pdf/NIG208055.pdf Nowak DJ, Greenfield EJ, Hoehn RE, Lapoint E. Carbon storage and sequestration by trees in urban and community areas of the United States. Environ Pollut. 2013;178:229–36. https://doi.org/10.1016/j.envpol.2013.03.019 . Oduwaye L, Ede P. Sustainable urban transport policies in Lagos: Assessing the BRT system. Cities. 2021;110:103067. https://doi.org/10.1016/j.cities.2020.103067 . OECD. Effective carbon rates 2021: Pricing carbon emissions through taxes and emissions trading. Organisation for Economic Co-operation and Development; 2021. Oladokun M, Akinola O. Sustainable building materials in Nigeria: Potentials and challenges. J Constr Developing Ctries. 2020;25(1):75–90. https://doi.org/10.21315/jcdc2020.25.1.5 . Omokaro GO. Multi-impacts of climate change and mitigation strategies in Nigeria: Agricultural production and food security. Sci One Health. 2025;4:100113. https://doi.org/10.1016/S2949704325000101 . Organisation for Economic Co-operation and Development; African Development Bank; Cities Alliance; UCLG Africa. (2025). Africa’s Urbanisation Dynamics 2025: Planning for Urban Expansion – Key messages: ECOWAS (West African Studies). OECD Publishing. https://doi.org/10.1787/2a47845c-en Orobator PO, Adahwara PO. Estimation of carbon storage and sequestration by tropical urban trees in Benin Metropolis, Edo State, Nigeria. Nigerian J Environ Sci Technol. 2022;6(1):214–24. https://doi.org/10.36263/nijest.2022.01.0347 . Ostrom E. Polycentric systems for coping with collective action and global environmental change. Glob Environ Change. 2010;20(4):550–7. https://doi.org/10.1016/j.gloenvcha.2010.07.004 . Page MJ, McKenzie JE, Bossuyt PM, Boutron I, Hoffmann TC, Mulrow CD, … and, Moher D. The PRISMA 2020 statement: An updated guideline for reporting systematic reviews. BMJ. 2021;372:n71. https://doi.org/10.1136/bmj.n71 . Paudel S, States SL. Urban green spaces and sustainability: Exploring the ecosystem services and disservices of grassy lawns versus floral meadows. Urban Forestry Urban Green. 2023;84:1618–8667. https://doi.org/10.1016/j.ufug.2023.127932 . Perini K, Rosasco P. Cost–benefit analysis for green façades and living wall systems. Build Environ. 2016;89:110–21. https://doi.org/10.1016/j.buildenv.2015.09.012 . Pirie G. (2013). Sustainable urban mobility in Anglophone Sub-Saharan Africa (Regional report for Global Report on Human Settlements 2013). UN-Habitat. https://unhabitat.org/sites/default/files/2013/06/GRHS.2013.Regional.Anglophone.Africa.pdf Psistaki K, Tsantopoulos G, Paschalidou AK. An Overview of the Role of Forests in Climate Change Mitigation. Sustainability. 2024;16(14):6089. https://doi.org/10.3390/su16146089 . Retta B, Coppola E, Ciniglia C, Grilli E. Constructed wetlands for the wastewater treatment: A review of Italian case studies. Appl Sci. 2023;13(10):6211. https://doi.org/10.3390/app13106211 . Sherman S, Fazeli H. (2022). Decarbonizing construction: The potential of cross-laminated timber. Chatham House Sustain Accelerator. https://accelerator.chathamhouse.org/article/decarbonizing-construction-the-potential-of-cross-laminated-timber Sicard P, Pascu I, Petrea S, Leca S, De Marco A, Paoletti E, Agathokleous E, Calatayud V. Effect of tree canopy cover on air pollution-related mortality in European cities: an integrated approach. Lancet Planet Health. 2025;9(6):e527–37. https://doi.org/10.1016/S2542-5196(25)00112-3 . Silva RH, Zwarteveen M, Stead D, Bacchin TK. Bringing Ecological Urbanism and Urban Political Ecology to transformative visions of water sensitivity in cities. Cities. 2024;145:104685. https://doi.org/10.1016/j.cities.2023.104685 . Singh T, Arpanaei A, Elustondo D, Wang Y, Stocchero A, West TAP, Fu Q. Emerging technologies for the development of wood products towards extended carbon storage and CO₂ capture. Carbon Capture Sci Technol. 2022;4:1–14. https://doi.org/10.1016/j.ccst.2022.100057 . Strohbach MW, Haase D. Above-ground carbon storage by urban trees in Leipzig, Germany: Analysis of patterns in relation to urban land use. Landsc Urban Plann. 2012;104(1):95–104. https://doi.org/10.1016/j.landurbplan.2011.10.001 . Tozluoğlu Ç, Liao Y, Sprei F. Potential of e-bikes to replace passenger car trips and reduce greenhouse gas emissions. J Cycl Micromobility Res. 2024;2., Article 100043. https://doi.org/10.1016/j.jcmr.2024.100043 . Tzaninis Y, Mandler T, Kaika M, Keil R. Moving urban political ecology beyond the ‘urbanization of nature’. Prog Hum Geogr. 2021;45(2):229–52. https://doi.org/10.1177/0309132520903350 . UNEP. Global waste management outlook 2020. United Nations Environment Programme; 2020. UN-Habitat. World cities report 2020: The value of sustainable urbanisation. UN-Habitat; 2020. Uwase M, Rwibasira P, Byiringiro J. Electrifying urban mobility in Kigali: Opportunities and challenges of e-motorcycles. Energy Policy. 2022;160:112653. https://doi.org/10.1016/j.enpol.2021.112653 . World Bank. (2023). Population, total Nigeria . Retrieved from https://data.worldbank.org/indicator/SP.POP.TOTL?locations=NG Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 13 Jan, 2026 Reviews received at journal 09 Jan, 2026 Reviews received at journal 08 Jan, 2026 Reviewers agreed at journal 31 Dec, 2025 Reviewers agreed at journal 31 Dec, 2025 Reviewers agreed at journal 30 Dec, 2025 Reviewers invited by journal 26 Dec, 2025 Editor invited by journal 05 Dec, 2025 Editor assigned by journal 04 Dec, 2025 Submission checks completed at journal 04 Dec, 2025 First submitted to journal 04 Dec, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8173067","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Systematic Review","associatedPublications":[],"authors":[{"id":566832044,"identity":"118d8dc4-c6ba-4435-999c-52b24a953351","order_by":0,"name":"Jolly Osaretin EGHAREVBA","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABFklEQVRIie2RsWrDMBCGzzU4S+zZoRC/goTX4LxKhMCeshc6RCEgL+leQx/CW93NxkMWl6yCdnApeOpQb81QUimZDHaydtA3iBP6P04nAWg0/xCDmetcFei8g6lc+fksH1IM1lH8q4qKdRTCAKyLihmvWTmGWfA8ev34tLMgSt82vG4zmDpi0d9jWyglpC/byPftii7T9yLGSQX+ZEh5JEopKcpDa5Jwc5kKwm9tDiS9rBwp2jejQ8JXEVLKL4fVFSUPkAgtaHm5OCny0WQxPEvxhKgMNKbbVjucCBLjB+7KeepeBcebov66C+ZoHxrfJLv3HBE19YHPPGfX3wUzgJsxOn1HB7c3rvDU5X4A5oMJjUaj0fwBHFhtvagfeJwAAAAASUVORK5CYII=","orcid":"","institution":"University of Benin","correspondingAuthor":true,"prefix":"","firstName":"Jolly","middleName":"Osaretin","lastName":"EGHAREVBA","suffix":""}],"badges":[],"createdAt":"2025-11-21 11:23:25","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8173067/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8173067/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":99209212,"identity":"5a1f4bb5-41e9-49bc-9a7f-b0b8eb93dd75","added_by":"auto","created_at":"2025-12-30 07:32:03","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":186147,"visible":true,"origin":"","legend":"","description":"","filename":"CarbonSequestrationasaFrameworkforUrbanFacilityPlanninginBeninMetro.docx","url":"https://assets-eu.researchsquare.com/files/rs-8173067/v1/434993ba9e1fa19343e8d401.docx"},{"id":99317421,"identity":"3aad7ce5-efab-45eb-8984-3c98706f4a4b","added_by":"auto","created_at":"2025-12-31 16:30:12","extension":"json","order_by":1,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":3605,"visible":true,"origin":"","legend":"","description":"","filename":"07ac22f4dd4c40a5b38b470348b0bf5f.json","url":"https://assets-eu.researchsquare.com/files/rs-8173067/v1/4b5fbaa316ab385f6a629ef0.json"},{"id":99209211,"identity":"c50d527c-b2ad-4c99-a97e-4818e9d9d9f7","added_by":"auto","created_at":"2025-12-30 07:32:03","extension":"xml","order_by":2,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":185072,"visible":true,"origin":"","legend":"","description":"","filename":"07ac22f4dd4c40a5b38b470348b0bf5f1enriched.xml","url":"https://assets-eu.researchsquare.com/files/rs-8173067/v1/39bd146fefd03e138a9b2e07.xml"},{"id":99209208,"identity":"8ece8cf0-a7e6-49c6-aeba-a93152440528","added_by":"auto","created_at":"2025-12-30 07:32:03","extension":"png","order_by":6,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":20013,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8173067/v1/e78afec080ce4c0688075f11.png"},{"id":99209210,"identity":"bee7accc-4f7d-45df-8de8-819b4fef2fc0","added_by":"auto","created_at":"2025-12-30 07:32:03","extension":"png","order_by":7,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":27892,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8173067/v1/d1d0110250a3cfc60c4854a7.png"},{"id":99317508,"identity":"5e675907-924a-4ced-93c7-34c8c22e9c06","added_by":"auto","created_at":"2025-12-31 16:30:18","extension":"png","order_by":8,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":30780,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8173067/v1/d400437491b577675a6b20c8.png"},{"id":99209213,"identity":"611d46d2-f2c2-4576-b938-85716aab7891","added_by":"auto","created_at":"2025-12-30 07:32:04","extension":"xml","order_by":9,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":183291,"visible":true,"origin":"","legend":"","description":"","filename":"07ac22f4dd4c40a5b38b470348b0bf5f1structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-8173067/v1/cd471159c2ac93f08a7fc69e.xml"},{"id":99318158,"identity":"0f1c1c25-aca4-4503-9080-3064a0d389b9","added_by":"auto","created_at":"2025-12-31 16:31:41","extension":"html","order_by":10,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":196133,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8173067/v1/8bc5c168f03ec696ad8eddf8.html"},{"id":99317681,"identity":"80b60422-533a-4d39-97cf-9df47c8e6679","added_by":"auto","created_at":"2025-12-31 16:30:35","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":54207,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eConceptual framework linking UPE, the Circular Bioeconomy, and Sustainable Urban Development Theory to carbon sequestration in urban facility planning in Benin Metropolis.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSource: Author’s Abstraction, 2025.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8173067/v1/76719b6e0749ce59c5c785c3.png"},{"id":99209204,"identity":"3a15ae5b-a5f6-42a4-bf68-c48fb0be7890","added_by":"auto","created_at":"2025-12-30 07:32:03","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":81910,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePRISMA Flowchart for Study Selection in Systematic Review of Carbon Sequestration in Urban Planning for Benin Metropolis, Nigeria\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSource: Author’s Abstraction, 20205.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8173067/v1/103d9a583adec5d7dc8a4e24.png"},{"id":99209206,"identity":"f50fca10-4e76-4690-a46e-75daac983ea4","added_by":"auto","created_at":"2025-12-30 07:32:03","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":198928,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eComparative Carbon Sequestration Potential by Facilities Type in Benin Metropolis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSource: Author’s Computation, 2025\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8173067/v1/17086bb3b5e23e56ace45c25.jpeg"},{"id":99323768,"identity":"3ee49918-50b2-482f-bb2a-4c0be2f9401a","added_by":"auto","created_at":"2025-12-31 16:46:11","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2281408,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8173067/v1/bb9eec73-fc13-4f2f-8d6b-0429d9b4d5d8.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Carbon Sequestration as a Framework for Urban Facility Planning in Benin Metropolis, Nigeria","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eCities today stand at the epicentre of the climate crisis, simultaneously representing both the source of the problem and the key to its solution. Globally, urban areas account for more than 70% of energy-related carbon dioxide (CO₂) emissions, despite covering only about 3% of the Earth\u0026rsquo;s land surface (IPCC, 2022). This concentration of emissions arises from the dense clustering of human activity, energy consumption, transport systems, industrial production, and construction. Yet, as centres of innovation, cities also hold the potential to lead the world towards climate solutions, particularly by rethinking how urban facilities are planned and managed. Rather than being passive emitters of carbon, urban spaces can be designed to act as carbon sinks through deliberate integration of carbon sequestration strategies. The urgency of such a paradigm shift is most evident in Africa, where urbanisation is unfolding at one of the fastest rates globally. By 2050, the continent\u0026rsquo;s urban population is projected to more than double, reaching nearly 1.4\u0026nbsp;billion (OECD et al., 2025). Nigeria, Africa\u0026rsquo;s most populous nation, epitomises this transformation. With over 223\u0026nbsp;million people in 2023 and a projected 400\u0026nbsp;million by 2050, Nigeria faces immense demographic pressures (World Bank, \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Cities such as Lagos, Abuja, Kano, and Benin Metropolis are experiencing unprecedented growth, driven by rural\u0026ndash;urban migration and natural population increases. Yet this growth is often unregulated, producing sprawling settlements, infrastructural deficits, and heightened environmental degradation (Jiboye et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn the heart of Edo State, Benin Metropolis stands as both a cultural hub and a city under intense environmental pressure. Accelerated urbanisation has come at the cost of deforestation, wetland loss, rising housing demand, unsustainable waste practices, and growing vehicular emissions. The removal of trees for residential estates has drastically reduced natural carbon sinks, while reliance on carbon-intensive materials such as cement and steel has deepened emissions. Furthermore, poor waste management practices, with organic waste dumped in open sites, generate methane that compounds climate impacts (Ike et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). These processes have left the city grappling with recurrent flooding, worsening heat stress, air pollution, and rising vulnerability for its poorest residents (Ede, 2019).\u003c/p\u003e \u003cp\u003eGlobally, urban sustainability debates are shifting from a narrow focus on emission reduction to a broader paradigm that combines reduction with active carbon removal and storage. This is the essence of carbon sequestration or \u0026ldquo;carbon gaining.\u0026rdquo; While traditional urban planning has prioritised efficiency better energy use, improved mobility, and enhanced waste management the scale of accumulated greenhouse gases now demands strategies that actively lock carbon away (Egharevba, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Carbon sequestration encompasses the capture and storage of atmospheric CO₂ in vegetation, soils, and building materials. When embedded in urban systems, facilities such as public buildings, transport corridors, waste plants, and wetlands can be reimagined to function simultaneously as service providers and carbon sinks (Churkina et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). This perspective reframes urban facilities as active agents in climate action. Mass timber construction, for instance, locks carbon into buildings while reducing reliance on high-emission materials (Singh et al., \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Urban forests and street trees absorb CO₂ while cooling neighbourhoods and enriching biodiversity. Composting and anaerobic digestion convert waste into soil carbon and renewable energy, while wetlands treat wastewater and sequester carbon in biomass and soils. Taken together, these interventions suggest that cities like Benin can transition from \u0026ldquo;carbon-losing\u0026rdquo; to \u0026ldquo;carbon-gaining.\u0026rdquo;\u003c/p\u003e \u003cp\u003eThe case for Benin Metropolis is particularly compelling. Unlike megacities such as Lagos, Benin reflects the realities of medium-sized African cities which is fast-growing, under-researched, and often overlooked in policy design (Cobbinah \u0026amp; Niminga-Beka, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Its medium scale offers flexibility for experimentation and innovation before infrastructural path dependencies become locked in (Parnell \u0026amp; Pieterse, 2014). Yet the city\u0026rsquo;s fragmented governance, informal settlements, weak enforcement of planning laws, and financial constraints mirror systemic challenges across sub-Saharan Africa.\u003c/p\u003e \u003cp\u003eNigeria\u0026rsquo;s climate commitments have intensified the urgency for sustainable urban transformation. As a signatory to the Paris Agreement, the country has pledged to achieve net-zero emissions by 2060 (Federal Government of Nigeria, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). However, progress toward this target remains uneven across sectors. In the energy sector, for instance, recent studies reveal conflicting trends efforts to promote a low-carbon energy transition coexist with continued investment in fossil fuel infrastructure, leading to persistent CO₂ emissions. Technological barriers, including ageing power grids, weak research and innovation capacity, and dependence on imported technologies, further slow the transition. Financial challenges such as poor fiscal policy implementation, weak investment frameworks, corruption, and limited access to renewable energy funding compound these problems (Atedhor, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). These national-level constraints are reflected in urban contexts, where inadequate financing, fragmented institutions, and limited technical capacity hinder the adoption of low-carbon strategies. Within this landscape, Benin Metropolis presents a critical opportunity to demonstrate how carbon sequestration can be effectively integrated into urban facility planning, aligning local actions with Nigeria\u0026rsquo;s broader climate goals and the global pursuit of sustainable development.\u003c/p\u003e \u003cp\u003eThis study responds to a critical gap in both scholarship and practice. While global evidence on urban carbon sequestration is expanding, research in sub-Saharan African cities remains sparse and fragmented. Strategies proven in temperate regions cannot be assumed to succeed in African contexts marked by constrained resources, institutional fragility, and socio-economic inequalities (Omokaro, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). By undertaking one of the limited systematic reviews and meta-analyses of carbon sequestration strategies in Nigerian cities, this research makes an original contribution. It synthesises international lessons while adapting them to the realities of Benin Metropolis, thereby providing a context-specific framework for action.\u003c/p\u003e \u003cp\u003eThe objectives are of threefold, first, to review global and African strategies for integrating carbon sequestration into urban facilities such as green infrastructure, sustainable buildings, transport, waste, and water systems; second, to contextualise these strategies within Benin\u0026rsquo;s socio-economic, ecological, and governance landscape; and third, to develop an integrative framework to guide policymakers, planners, and communities.\u003c/p\u003e \u003cp\u003eThe significance of this study lies in its dual contribution. Academically, it advances debates on sustainable urbanism by embedding carbon sequestration within African urban contexts. Practically, it offers policymakers in Benin Metropolis and similar medium-sized cities a roadmap for transforming facilities into carbon sinks. Beyond climate mitigation, the co-benefits including reduced flooding, improved air quality, cooling, livelihoods, and public health make the case for urgent action. Ultimately, the study emphasises that the future of Benin Metropolis is not predetermined. With deliberate choices, it can emerge as a carbon-gaining, resilient city that advances both Nigeria\u0026rsquo;s net-zero ambitions and global debates on sustainable urban futures in the Global South.\u003c/p\u003e"},{"header":"2. Theoretical Framework","content":"\u003cp\u003eEvery research endeavour rests upon conceptual foundations that guide its arguments, sharpen its analytical lens, and lend coherence to its findings. For this study, three interlinked paradigms are mobilised: Urban Political Ecology (UPE), the Circular Bioeconomy, and Sustainable Urban Development Theory. Together, these frameworks provide a multidimensional perspective on how urban facilities in Benin Metropolis currently function, how they may be re-imagined as carbon sinks, and what political, economic, and ecological conditions shape this transformation.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Urban Political Ecology (UPE)\u003c/h2\u003e \u003cp\u003eUrban Political Ecology (UPE) emerged in the 1990s as an extension of political ecology into urban contexts, interrogating how power, politics, and inequality underpin the production of urban environments (Tzaninis et al., \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Silva et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). It challenges the perception that environmental issues in cities are purely technical or natural. Instead, it emphasises that they are deeply political rooted in decisions about who benefits from development, who bears environmental costs, and how resources are allocated (Swyngedouw \u0026amp; Heynen, 2003).\u003c/p\u003e \u003cp\u003eApplied to Benin Metropolis, UPE reveals the political-economic dynamics underlying its carbon-intensive growth. The replacement of forests and wetlands with housing estates is not merely a response to population pressures but also reflects governance decisions that prioritise short-term revenue from land allocation and speculative real estate development over long-term ecological resilience. Similarly, failures in waste management are not only technical inefficiencies but reflect power struggles between local authorities, private contractors, and informal waste pickers (Egharevba \u0026amp;Onaiwu, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). These governance tensions persist despite Nigeria\u0026rsquo;s Climate Change Act (2021), which mandates emission reduction targets and institutional frameworks for climate action. UPE highlights how weak enforcement of this legislation at the city level risks undermining national ambitions, as fragmented urban governance leaves room for elite capture and marginalisation of vulnerable groups.\u003c/p\u003e \u003cp\u003eUPE also illuminates the unequal distribution of environmental burdens. In Benin Metropolis, low-income residents disproportionately live-in flood-prone areas with inadequate drainage and minimal green cover. These communities face the highest risks from flooding, heat stress, and poor air quality while contributing the least to emissions (Heynen et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Akinyemi \u0026amp; Ogunleye, 2021). This resonates with UPE\u0026rsquo;s central claim: urban environmental crises mirror broader socio-political inequalities. From this perspective, transforming facilities into carbon sinks is not simply about technical fixes but about addressing governance and justice concerns. Unless interventions are designed inclusively, carbon sequestration projects could reproduce or even intensify inequalities for example, displacing informal settlers to create green spaces. By tying these insights to Nigeria\u0026rsquo;s evolving climate governance, UPE grounds the study in the reality that achieving the Climate Change Act\u0026rsquo;s carbon budgets depends on aligning national frameworks with local justice and accountability mechanisms.\u003c/p\u003e \u003cp\u003eIn this study, UPE therefore provides a critical lens to ask: \u003cem\u003eCarbon for whom? Who gains and who loses from carbon-gaining facilities?\u003c/em\u003e These questions ensure that strategies are not only ecologically effective but also socially just, anchoring climate action in equity and fairness.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 The Circular Bioeconomy Concept\u003c/h2\u003e \u003cp\u003eWhile UPE foregrounds politics and justice, the Circular Bioeconomy offers a complementary economic ecological paradigm. Broadly, the bioeconomy refers to the use of renewable biological resources such as forests, crops, and organic waste to produce food, energy, and materials. When combined with circular economy principles, it moves beyond the traditional linear \u0026ldquo;take\u0026ndash;make\u0026ndash;dispose\u0026rdquo; model towards one where biological materials are reused, recycled, and regenerated (Korhonen et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFor Benin Metropolis, this paradigm provides practical strategies for integrating carbon sequestration into everyday facilities. In buildings, the use of mass timber or bamboo locks carbon for decades, reducing dependence on cement and steel, whose production is highly carbon-intensive (Churkina et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). In waste management, composting and anaerobic digestion transform organic waste streams from methane emitters into carbon sinks and renewable energy sources (Bernstad \u0026amp; la Cour Jansen, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). In water infrastructure, constructed wetlands recycle wastewater while sequestering carbon in soils and biomass (Retta et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe Circular Bioeconomy resonates strongly with African contexts. In Benin Metropolis, informal recycling, composting, and urban farming are already widespread, though often marginalised from official policy. By formally recognising and supporting these practices, planners could enhance both carbon sequestration and livelihoods (Orobator \u0026amp; Adahwara, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Here again, connections to the Climate Change Act (2021) are instructive: while the Act sets national emission reduction goals, the Circular Bioeconomy demonstrates how grassroots resource efficiency can be scaled and integrated into governance frameworks to operationalise those goals. Importantly, the Circular Bioeconomy challenges the notion that sustainability must be costly. Instead, it highlights efficiency, innovation, and value creation from waste. By reframing biological systems as economic assets, it opens pathways for green entrepreneurship, job creation, and more resilient urban economies in Nigeria.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Sustainable Urban Development Theory\u003c/h2\u003e \u003cp\u003eThe third pillar of this framework is Sustainable Urban Development Theory, which argues that cities can and must grow in ways that balance economic expansion, environmental protection, and social equity (Campbell, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1996\u003c/span\u003e). It provides the normative foundation for sustainable urban planning, insisting that urban development should not come at the expense of ecological integrity or social well-being.\u003c/p\u003e \u003cp\u003eIn Nigeria, however, urban development has historically emphasised economic growth over sustainability. In Benin Metropolis, housing estates often spring up without green space provision or energy-efficient design. Roads are expanded to accommodate private vehicles while public transport and cycling infrastructure receive limited investment. This trajectory deepens carbon dependency and undermines liveability.\u003c/p\u003e \u003cp\u003eSustainable Urban Development Theory challenges this model by advancing planning principles such as compact growth, mixed land use, transit-oriented development, and biophilic design. It stresses that sustainability is not a luxury reserved for wealthy nations but a necessity for rapidly growing cities in the Global South. Embedding sustainability at this stage of Benin\u0026rsquo;s growth is crucial to avoid locking the city into a high-carbon future (UN-Habitat, \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Within this study, the theory provides the \u003cem\u003e\u0026ldquo;why\u0026rdquo;\u003c/em\u003e the normative justification for embedding carbon sequestration into every facility, from schools and hospitals to markets and drainage systems.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Synthesising the Frameworks\u003c/h2\u003e \u003cp\u003eIndividually, UPE, the Circular Bioeconomy, and Sustainable Urban Development each illuminate vital aspects of urban carbon sequestration. UPE exposes the socio-political inequalities shaping environmental outcomes, reminding us that carbon strategies must be just. The Circular Bioeconomy operationalises this vision, providing mechanisms to transform linear, resource-depleting infrastructures into regenerative, carbon-storing systems. Sustainable Urban Development, in turn, anchors both within a long-term normative vision of balanced growth and climate-compatible cities.\u003c/p\u003e \u003cp\u003eWhen synthesised, these frameworks generate a holistic analytical foundation. UPE demands attention to governance and justice, the Circular Bioeconomy explains \u003cem\u003ehow\u003c/em\u003e to operationalise carbon sequestration, and Sustainable Urban Development outlines \u003cem\u003ewhy\u003c/em\u003e it must be embedded as a core principle. Together, they reinforce the central argument of this study: carbon sequestration is not an optional add-on but a transformative organising principle for urban planning in Benin Metropolis. See Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e for the interaction between the frameworks.\u003c/p\u003e\u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Relevance to Benin Metropolis\u003c/h2\u003e \u003cp\u003eFor Benin Metropolis, these frameworks are especially pertinent. UPE reveals how governance fragmentation among local, state, and federal authorities constrains coherent planning. The Circular Bioeconomy resonates with the city\u0026rsquo;s strong informal economy and agricultural hinterland, offering strategies to align carbon sequestration with livelihoods and resource efficiency. Sustainable Urban Development underscores the urgency of embedding carbon-gaining practices now, before the city\u0026rsquo;s infrastructural trajectory becomes locked into unsustainable patterns. Crucially, situating these insights within the implementation of Nigeria\u0026rsquo;s Climate Change Act (2021) strengthens the relevance of this study. The Act sets a national mandate for emission reduction and climate resilience, but its success depends on local application. By linking UPE\u0026rsquo;s governance critique, the Circular Bioeconomy\u0026rsquo;s practical pathways, and Sustainable Urban Development\u0026rsquo;s normative principles, this framework shows how Benin Metropolis can translate national commitments into grounded, context-specific action.\u003c/p\u003e \u003cp\u003eTaken together, the three frameworks illuminate both the barriers and opportunities facing Benin Metropolis. They affirm that transforming facilities into carbon sinks requires not only new technologies but also shifts in governance, cultural values, and economic systems. By grounding this study in UPE, the Circular Bioeconomy, and Sustainable Urban Development Theory, the analysis moves beyond technical prescriptions to a deeper understanding of the socio-ecological systems that will shape Benin Metropolis\u0026rsquo;s climate future.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Literature Review","content":"\u003cp\u003eOver the past two decades, literature on urban carbon sequestration has expanded considerably, reflecting a growing awareness of the crucial role cities play in addressing climate change crisis. Research in this field generally clusters around three interconnected strategies: reducing emissions, enhancing carbon sinks, and reshaping governance systems. Bulk of this evidence, however, stems from Europe, North America, and Asia, where studies have demonstrated the technical feasibility and economic value of diverse interventions. In contrast, contributions from African contexts particularly sub-Saharan cities remain limited. This imbalance leaves an important gap for fast-growing cities like Benin, where rapid urbanisation and ecological degradation intersect. To address this, the present review draws on global, regional, and Nigerian literature across five thematic domains green infrastructure, sustainable building materials and design, transportation, waste and water management, and governance before identifying the gaps and opportunities most pertinent to Benin Metropolis.\u003c/p\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Green Infrastructure\u003c/h2\u003e \u003cp\u003eGreen infrastructure including urban forests, street trees, parks, wetlands, and green roofs has emerged as one of the most documented strategies for urban carbon sequestration. Scholars consistently emphasise that vegetation not only absorbs CO₂ but also generates co-benefits such as cooling, biodiversity conservation, stormwater regulation, and enhanced liveability (Gill et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Nowak et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). For instance, Nowak et al. (\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) estimated that urban trees in the United States sequester approximately 22.8\u0026nbsp;million tonnes of carbon annually, while researches showed that European tree canopy cover can offset significant local emissions (European Forest Institute n.d.; Psistaki et al., \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Sicard et al., \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). At the micro level, each urban tree can sequester 20\u0026ndash;50 kg of CO₂ annually, while green roofs contribute between 0.5 and 2.5 kg CO₂ per square metre each year (Getter et al., 2009).\u003c/p\u003e \u003cp\u003eIn African cities, however, greening efforts encounter systemic challenges. Weak institutional frameworks, insecure land tenure, and limited maintenance capacity often undermine implementation (Cobbinah \u0026amp; Niminga-Beka, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). In Accra, rapid urban expansion has eroded green cover despite policies advocating tree planting (du Toit et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Nigerian studies reveal similar tensions: while urban trees and parks offer potential for meaningful carbon storage, sustainability is jeopardised by vandalism, poor enforcement, and low public awareness (Alabi, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Dipeolu, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Adegun et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFor Benin Metropolis, located within a tropical forest zone yet experiencing rapid deforestation and land conversion, green infrastructure is particularly salient. The replacement of vegetation with asphalt has amplified heat and flood risks. Strategic initiatives such as community-led tree planting, integration of green roofs, and urban reforestation could both sequester carbon and improve liveability. Yet their success depends on tackling governance fragmentation, securing land tenure, and mobilising financial resources. Robust policy support, as well as community buy-in, will be indispensable for sustaining gains.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Carbon-Negative Building Materials and Design\u003c/h2\u003e \u003cp\u003eThe construction sector is a global hotspot for emissions, accounting for nearly 40% of energy-related CO₂ emissions (IEA, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Much of this stems from the embodied carbon of cement and steel. As a response, scholars and practitioners are exploring carbon-negative or low-carbon building materials. Churkina et al. (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) argue that widespread adoption of mass timber construction could lock away carbon for decades, with models suggesting up to 20 gigatonnes of storage potential by 2050 if half of global new construction shifted to timber. Similarly, bamboo, hempcrete, and other bio-based alternatives provide promising pathways (Firoozi et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003ePilot projects in Europe and North America, particularly those deploying Cross-Laminated Timber (CLT), demonstrate reduced embodied energy, faster construction times, and long-term carbon storage (Ahmed \u0026amp; Arocho, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Sherman \u0026amp; Fazeli, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). CLT has been shown to reduce embodied carbon by over 60% compared to conventional concrete and steel (Churkina et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Green roofs further complement this by sequestering CO₂ while providing cooling benefits (Getter et al., 2009).\u003c/p\u003e \u003cp\u003eIn Nigeria, research into sustainable building practices is emerging. Oladokun and Akinola (\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) highlight bamboo and timber\u0026rsquo;s potential, but note challenges of quality assurance, cultural perceptions, and outdated codes. Chima (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2025\u003c/span\u003e) emphasised the need for updated building regulations and investment in local supply chains that are eco-friendly. For Benin Metropolis, situated near resource-rich Edo forests, opportunities exist to develop localised timber-based construction systems. However, unchecked exploitation risks deforestation, highlighting the need for sustainable forestry management. Retrofitting older buildings with insulation, efficient lighting, and solar energy remains underexplored but offers parallel opportunities.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Transportation and Mobility\u003c/h2\u003e \u003cp\u003eGlobally, transportation contributes about 24% of energy-related CO₂ emissions, with road vehicles as the dominant source (IEA, 2023). Research demonstrates the importance of promoting active mobility (cycling, walking), electrifying fleets, and expanding mass transit systems to reduce emissions and improve air quality (Creutzig et al., 2015).\u003c/p\u003e \u003cp\u003eIn African contexts, transport is dominated by informal minibuses, motorcycles, and ageing fleets with poor efficiency (Pirie, \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Innovations such as Lagos\u0026rsquo; Bus Rapid Transit (BRT) showcase how investments in public transport can simultaneously cut emissions and reduce travel times (Oduwaye \u0026amp; Ede, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Kigali\u0026rsquo;s electric motorcycle initiatives further highlight scalable low-carbon mobility (Uwase et al., \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eBenin Metropolis mirrors these regional challenges: limited mass transit, growing private vehicle ownership, and rising congestion. Research indicates that electrifying buses, investing in cycling infrastructure, and redesigning road systems for mixed-use transport could substantially reduce emissions (Cai et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Tozluoğlu et al., \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Such measures indirectly support carbon sequestration by cutting fossil fuel reliance. Importantly, mobility transitions require behavioural shifts supported by incentives, subsidies, and awareness campaigns. Without cultural acceptance and strong governance, adoption is likely to falter.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Waste and Water Management\u003c/h2\u003e \u003cp\u003eWaste and water infrastructure present both risks and opportunities. Globally, waste contributes about 5% of greenhouse gas emissions, particularly methane from landfills (UNEP, \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Conversely, strategies such as composting, anaerobic digestion, and bioenergy generation can divert organic waste into carbon-storing pathways (Bernstad \u0026amp; la Cour Jansen, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Constructed wetlands, with sequestration potential of 100\u0026ndash;200 g C per square metre annually, provide cost-effective solutions for wastewater treatment, flood control, and biodiversity conservation (Maucieri et al., 2017; Retta et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn Nigeria, most cities including Benin struggle with open dumping, low recycling rates, and weak formal systems (Ike et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Yet the informal sector plays a vital role in recycling plastics, metals, and organic waste. Formalising and supporting these actors could enhance both efficiency and equity. Decentralised composting hubs and small-scale biogas units align with Benin\u0026rsquo;s resource constraints and offer scalable solutions. Integrating wetlands into peri-urban zones could also enhance ecosystem services while supporting sequestration.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Community Engagement and Policy Frameworks\u003c/h2\u003e \u003cp\u003eTechnical strategies alone cannot guarantee sustainability; social and institutional dynamics are equally crucial. Evidence suggests that community participation in greening, waste segregation, and mobility projects enhances ownership, reduces vandalism, and ensures long-term viability (Brown \u0026amp; Taylor, 2020; Paudel \u0026amp; States, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Muhoza \u0026amp; Zhou, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Kamana et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Kochsk\u0026auml;mper et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Community engagement builds resilience and social capital, both vital for adapting to climate change impacts.\u003c/p\u003e \u003cp\u003ePolicy and governance frameworks create the enabling conditions. Globally, instruments such as carbon pricing, green building codes, and mandatory urban greening drive substantial progress (OECD, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In Nigeria, the 2021 Climate Change Act is a milestone, mandating carbon budgets and governance structures (Federal Government of Nigeria, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Yet integration at the municipal level remains weak, with city plans rarely embedding carbon sequestration explicitly. For Benin Metropolis, aligning the Master Plan with carbon goals, reforming building codes, and strengthening participatory governance could unlock significant opportunities. Partnerships across government, private actors, and civil society will be critical to financing and scaling interventions.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.6 Identified Gaps\u003c/h2\u003e \u003cp\u003eDespite progress in global scholarship, gaps remain highly relevant for Benin Metropolis. First, African contexts are underrepresented, with most empirical data drawn from developed regions. Second, interventions are often studied in isolation tree planting, waste, or mobility rather than integrated into cohesive frameworks. Third, socio-political dimensions of justice, equity, and governance remain underexplored, despite their critical importance. Finally, there is little empirical measurement of sequestration potential within Nigerian ecological contexts, hampering evidence-based policymaking.\u003c/p\u003e \u003cp\u003eThese gaps reinforce the significance of this study, which synthesises diverse global insights while contextualising them for Benin Metropolis. By drawing together strategies across green infrastructure, sustainable buildings, mobility, waste systems, and participatory governance, the research seeks to fill a crucial void in both academic discourse and urban planning practice.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Methodology","content":"\u003cp\u003eThe research adopted a systematic and comprehensive approach due to the dispersed and multidisciplinary nature of relevant studies spanning urban planning, geography, ecology, architecture, engineering, and the social sciences. A systematic review combined with meta-analysis was selected as the most suitable methodology. This dual design enabled the synthesis of diverse evidence, identification of recurring patterns, and generation of insights contextualised to Benin Metropolis, Nigeria.\u003c/p\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Research Design\u003c/h2\u003e \u003cp\u003eThe study employed a systematic review and meta-analytic framework guided by the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines (Page et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Unlike traditional literature reviews, this approach follows a transparent, replicable process of identifying, screening, and synthesising studies. Where feasible, meta-analysis allowed for the aggregation of quantitative findings, such as the carbon sequestration potential of trees, green roofs, or mass timber. This design was chosen to capture both the breadth of available research and enable comparative evaluation, providing policymakers and planners with robust benchmarks.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Data Sources and Search Strategy\u003c/h2\u003e \u003cp\u003eTo build a comprehensive evidence base, the study searched multiple academic databases, including Scopus, Web of Science, PubMed, Google Scholar, and JSTOR. Grey literature was also consulted, including reports from the Intergovernmental Panel on Climate Change, UN-Habitat, and Nigeria\u0026rsquo;s Federal Ministry of Environment. This ensured that both academic and policy-driven evidence were captured.\u003c/p\u003e \u003cp\u003eSearch terms were structured around urban planning, carbon sequestration, and facility-based interventions, using Boolean operators such as:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003e(\u0026ldquo;urban planning\u0026rdquo; OR \u0026ldquo;urban facility\u0026rdquo; OR \u0026ldquo;infrastructure\u0026rdquo;) AND (\u0026ldquo;carbon sequestration\u0026rdquo; OR \u0026ldquo;carbon sink\u0026rdquo;)\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e(\u0026ldquo;green infrastructure\u0026rdquo; OR \u0026ldquo;urban forest\u0026rdquo; OR \u0026ldquo;green roof\u0026rdquo;) AND (\u0026ldquo;climate mitigation\u0026rdquo; OR \u0026ldquo;carbon storage\u0026rdquo;)\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e(\u0026ldquo;mass timber\u0026rdquo; OR \u0026ldquo;bio-based materials\u0026rdquo;) AND (\u0026ldquo;city\u0026rdquo; OR \u0026ldquo;urban\u0026rdquo;)\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e(\u0026ldquo;waste management\u0026rdquo; OR \u0026ldquo;composting\u0026rdquo; OR \u0026ldquo;anaerobic digestion\u0026rdquo;) AND (\u0026ldquo;carbon sequestration\u0026rdquo; OR \u0026ldquo;greenhouse gases\u0026rdquo;)\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e(\u0026ldquo;constructed wetlands\u0026rdquo; OR \u0026ldquo;wastewater treatment\u0026rdquo;) AND (\u0026ldquo;carbon storage\u0026rdquo; OR \u0026ldquo;emission reduction\u0026rdquo;)\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eThe review was limited to studies published between 2000 and 2025, reflecting the period of heightened global attention to climate change and the rise of sustainable urbanism.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e4.3 Inclusion and Exclusion Criteria\u003c/h2\u003e \u003cp\u003eTo ensure methodological rigour, inclusion criteria focused on peer-reviewed articles, book chapters, or credible institutional reports dealing specifically with carbon sequestration in urban contexts. Studies presenting empirical data quantitative or qualitative were prioritised, especially those addressing buildings, transport, waste, water systems, and green infrastructure. Only English-language publications were considered. Exclusion criteria ruled out studies focused exclusively on rural landscapes, forestry plantations, or large-scale geoengineering such as carbon capture and storage (CCS). Articles without empirical data, purely theoretical pieces, duplicates, and grey literature lacking transparency were also excluded. These criteria ensured that the reviewed evidence remained both relevant and robust.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e4.4 Screening and Selection Process\u003c/h2\u003e \u003cp\u003eThe search yielded about 1,500 records. After removing duplicates, 1,200 studies remained. Screening of titles and abstracts reduced this to 210, and full-text review against the criteria resulted in 60 studies being included in the qualitative synthesis and 40 in the meta-analysis. The PRISMA flow diagram (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) documents each stage of identification, screening, eligibility, and inclusion, ensuring transparency and replicability.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e4.5 Data Extraction and Analysis\u003c/h2\u003e \u003cp\u003eFrom each included study, variables such as intervention type (e.g., trees, mass timber, wetlands), geographic location, and carbon sequestration potential (e.g., CO₂ stored per year or embodied carbon avoided) were extracted. Co-benefits including cooling, flood control, biodiversity, and energy generation were noted alongside barriers and enabling factors such as governance, finance, and community engagement.\u003c/p\u003e \u003cp\u003eData were thematically coded into categories corresponding to urban facilities: green infrastructure, buildings, transport, waste, and water. Meta-analysis was used to calculate pooled effect sizes where comparable data existed (e.g., tree sequestration rates), while qualitative synthesis captured governance, policy, and social insights.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003e4.6 Validity and Reliability Measures\u003c/h2\u003e \u003cp\u003eTo enhance reliability, multiple databases were searched, peer-reviewed and transparent studies were prioritised, and a standardised template guided data extraction. Triangulation was achieved by combining academic and grey literature.\u003c/p\u003e \u003cp\u003eHowever, key limitations remain. The scarcity of empirical studies from African cities limited the strength of the meta-analysis for some interventions, and adapting global findings to Benin Metropolis required careful contextualisation. This challenge underscores the need for more localised research to strengthen the evidence base.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003e4.7 Justification for Methodological Approach\u003c/h2\u003e \u003cp\u003eThe choice of a systematic review with meta-analysis was deliberate. Urban carbon sequestration remains a relatively new field, with evidence fragmented across disciplines and geographies. For policymakers in Benin Metropolis, fragmented insights are insufficient; what is required is a consolidated, evidence-based framework. This methodology enables such integration, offering both breadth and depth.\u003c/p\u003e \u003cp\u003eThe meta-analytic component provides quantitative benchmarks for example, the average annual carbon sequestration capacity of urban trees or the comparative efficiency of constructed wetlands. Meanwhile, the systematic review component illuminates governance and socio-political barriers, ensuring strategies are not only technically feasible but also socially and institutionally viable.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec23\" class=\"Section2\"\u003e \u003ch2\u003e4.8 Relevance to Benin Metropolis\u003c/h2\u003e \u003cp\u003eApplying this methodology to Benin Metropolis is particularly valuable because the city lacks localised empirical research on carbon sequestration. By synthesising global lessons and adapting them to local realities, this study bridges a critical knowledge gap. The thematic synthesis offers a decision-making blueprint, helping policymakers evaluate which strategies community tree planting, mass timber construction, decentralised composting, or constructed wetlands are most viable within Benin\u0026rsquo;s ecological, economic, and governance conditions.\u003c/p\u003e \u003cp\u003eUltimately, this methodological design ensures that the recommendations produced are not mere imports of Western practices but a critically adapted framework tailored to the specific challenges and opportunities of an African city. It balances academic rigour with practical relevance, ensuring that findings can guide both scholarship and actionable policy in Benin Metropolis.\u003c/p\u003e \u003c/div\u003e"},{"header":"5. Results and Findings","content":"\u003cp\u003eThis study synthesised evidence from North America, Europe, Asia, and Africa to assess the feasibility of integrating carbon sequestration into urban facility planning. The findings confirmed that such integration is not only technically viable but also capable of delivering substantial environmental, social, and economic co-benefits. For Benin Metropolis, the strongest opportunities lie in expanding green infrastructure, adopting carbon-negative building design, advancing sustainable mobility, and deploying circular waste and water management systems. Collectively, these interventions offer a pathway for the city to transition from being a net carbon source to a carbon sink.\u003c/p\u003e \u003cdiv id=\"Sec25\" class=\"Section2\"\u003e \u003ch2\u003e5.1 Green Infrastructure Facilities\u003c/h2\u003e \u003cp\u003eAcross all facility categories, urban green infrastructure emerged as the most powerful contributor to carbon sequestration. Meta-analysis confirms that mature urban trees sequester between 20\u0026ndash;50 kg of CO₂ per tree annually, depending on species, age, and climatic conditions (Nowak et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Green roofs, while less impactful per unit, absorb 0.5\u0026ndash;2.5 kg of CO₂ per square metre each year, and at scale provide meaningful gains (Getter \u0026amp; Rowe, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Urban parks that integrate native tree species demonstrate long-term carbon storage advantages over ornamental landscapes (Strohbach \u0026amp; Haase, \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2012\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAfrican evidence reveals significant challenges, particularly weak institutional frameworks that undermine tree planting initiatives (Cobbinah \u0026amp; Niminga-Beka, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Nevertheless, successful case studies from Nairobi and Accra illustrate that community-driven greening, supported by strong stewardship, can deliver lasting benefits. For Benin Metropolis, interventions such as planting native, high-biomass species along streets and in parks, mandating street tree corridors, and incentivising rooftop greening could significantly boost sequestration while mitigating heat islands and flood risks.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec26\" class=\"Section2\"\u003e \u003ch2\u003e5.2 Public Buildings and Carbon-Negative Materials\u003c/h2\u003e \u003cp\u003eBuildings represent another high-potential sector for carbon sequestration. Studies on mass timber and Cross-Laminated Timber (CLT) construction demonstrate reductions of over 60% in embodied carbon compared to conventional concrete and steel (Churkina et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). A CLT building can store between 500\u0026ndash;700 kg of CO₂ per square metre of floor area, effectively locking carbon for the lifetime of the structure (Ahmed \u0026amp; Arocho, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Sherman \u0026amp; Fazeli, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eComplementary strategies include integrating green roofs and bio-based insulation. Life cycle analyses show these measures not only offset embodied emissions but also enhance sequestration and cooling effects (Perini \u0026amp; Rosasco, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). In tropical contexts, bamboo, hempcrete, and other bio-based alternatives have demonstrated potential to reduce lifecycle emissions while supporting affordable housing (Firoozi et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn Nigeria, however, adoption is hindered by cultural preferences for concrete, outdated building codes, and perceptions of timber as \u0026ldquo;inferior\u0026rdquo; (Oladokun \u0026amp; Akinola, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). For Benin Metropolis, proximity to forest resources in Edo State offers a unique opportunity to establish sustainable supply chains, provided governance mechanisms safeguard against overharvesting. Pilot projects, for example, constructing a public library or school using mass timber could demonstrate feasibility, update perceptions, and build confidence in carbon-negative building practices.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec27\" class=\"Section2\"\u003e \u003ch2\u003e5.3 Transportation and Mobility Systems\u003c/h2\u003e \u003cp\u003eTransportation remains a dominant source of urban emissions. Globally, the sector accounts for about 24% of energy-related CO₂ emissions (IEA, 2023). The review shows that mass transit investment, active transport promotion, and vehicle electrification reduce emissions significantly. Electrifying bus fleets in Chinese and European cities cut emissions by 30\u0026ndash;50%, depending on energy sources (Liu et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Similarly, cycling networks and pedestrian infrastructure reduce short car trips, indirectly lowering carbon footprints (Creutzig et al., 2015).\u003c/p\u003e \u003cp\u003eAfrican experiences reinforce this potential. Lagos\u0026rsquo; Bus Rapid Transit (BRT) system cut travel time by 40% and lowered corridor CO₂ emissions by 13% within five years (Oduwaye \u0026amp; Ede, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), while Kigali pioneered electric motorcycles as a scalable model of low-carbon mobility (Uwase et al., \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). For Benin Metropolis, dominated by private cars, minibuses, and motorcycles, the most viable interventions include piloting electric buses, electrifying minibuses, and investing in safe pedestrian and cycling infrastructure. While transport does not directly sequester carbon, reducing reliance on fossil fuels substantially improves the city\u0026rsquo;s net carbon balance.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec28\" class=\"Section2\"\u003e \u003ch2\u003e5.4 Waste and Water Management Facilities\u003c/h2\u003e \u003cp\u003eWaste management systems present both critical challenges and untapped opportunities. Globally, diverting organic waste from landfills through composting avoids emissions of approximately 0.27 tonnes of CO₂-equivalent methane per tonne of waste while adding about 0.1 tonnes of CO₂-equivalent to soils through carbon-rich compost (Bernstad \u0026amp; la Cour Jansen, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Boldrin et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Anaerobic digestion offers additional benefits by producing biogas that offsets fossil fuel use.\u003c/p\u003e \u003cp\u003eConstructed wetlands provide complementary carbon gains, sequestering 100\u0026ndash;200 grams of carbon per square metre annually while delivering water purification, stormwater management, and habitat creation (Retta et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Brix \u0026amp; Arias, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). Case studies in Asia show wetlands to be cost-effective and resilient alternatives to energy-intensive wastewater treatment.\u003c/p\u003e \u003cp\u003eIn Nigeria, however, most cities including Benin rely on open dumping and poorly managed landfills, with limited composting infrastructure (Ike et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). The findings suggest that even decentralised composting units and small-scale biogas plants could dramatically reduce emissions while creating fertiliser, renewable energy, and green jobs. Integrating constructed wetlands into drainage and wastewater systems could further address Benin\u0026rsquo;s recurrent flooding while enhancing sequestration.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec29\" class=\"Section2\"\u003e \u003ch2\u003e5.5 Community Engagement and Governance\u003c/h2\u003e \u003cp\u003eA consistent insight across facility types is the centrality of community participation. Evidence from Africa and beyond shows that tree planting, waste segregation, and neighbourhood greening initiatives succeed when communities are actively involved in design and maintenance (Paudel \u0026amp; States, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Muhoza \u0026amp; Zhou, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Policy frameworks are equally critical: supportive legislation, updated building codes, and participatory governance structures enable technical solutions to succeed (OECD, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Federal Government of Nigeria, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). For Benin Metropolis, embedding carbon goals into the Master Plan, mandating waste segregation, and promoting public awareness campaigns will be vital.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec30\" class=\"Section2\"\u003e \u003ch2\u003e5.6 Comparative Impact Assessment\u003c/h2\u003e \u003cp\u003eComparing the carbon sequestration potential of different urban facilities is essential for identifying priority areas where interventions can yield the greatest environmental and socio-economic benefits. While each facility type green infrastructure, buildings, transport, waste, and water systems offers distinct pathways for reducing emissions or enhancing carbon sinks, their impacts vary significantly in scale, feasibility, and co-benefits. A comparative assessment provides clarity on which interventions hold the greatest promise for Benin Metropolis, were resource constraints and rapid urbanisation demand carefully targeted strategies. By weighing both direct carbon gains and indirect contributions such as cooling, flood control, and improved mobility, this assessment highlights not only the technical potential of each facility but also its contextual relevance. The synthesis of findings across facility types area summarised in the Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCarbon Sequestration Potential by Facility Type\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFacility Type\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eIntervention\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eEstimated Carbon Impact\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eContextual Relevance to Benin Metropolis\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSource\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGreen Infrastructure\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTrees, parks, green roofs\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e20\u0026ndash;50kg CO₂/tree/year; 0.5\u0026ndash;2.5kg CO₂/m\u0026sup2;/year (roofs)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eHigh potential; limited by land competition and weak maintenance capacity\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNowak et al. (\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2013\u003c/span\u003e); Getter \u0026amp; Rowe (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2006\u003c/span\u003e); Strohbach \u0026amp; Haase (\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2012\u003c/span\u003e); Cobbinah \u0026amp; Niminga-Beka (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2017\u003c/span\u003e); Orobator \u0026amp; Adahwara (\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2022\u003c/span\u003e); Dipeolu (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2021\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBuildings\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMass timber, bio-based materials, retrofits\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e60%+ reduction in embodied carbon; 500\u0026ndash;700kg CO₂/m\u0026sup2; stored\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eStrong potential given forest resources; requires policy reforms and updated codes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eChurkina et al. (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2020\u003c/span\u003e); Ahmed \u0026amp; Arocho (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2020\u003c/span\u003e); Sherman \u0026amp; Fazeli (\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2022\u003c/span\u003e); Perini \u0026amp; Rosasco (\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2016\u003c/span\u003e); Firoozi et al. (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2024\u003c/span\u003e); Oladokun \u0026amp; Akinola (\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2020\u003c/span\u003e); Chima (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2025\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTransport\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEVs, mass transit, active transport\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e30\u0026ndash;50% reduction in emissions (indirect effect)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFeasible with pilot EV projects and improved public transit\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eLiu et al. (\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2019\u003c/span\u003e); IEA (2023); Oduwaye \u0026amp; Ede (\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2021\u003c/span\u003e); Uwase et al. (\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2022\u003c/span\u003e); Cai et al. (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2024\u003c/span\u003e); Tozluoğlu et al. (\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2024\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWaste Facilities\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eComposting, anaerobic digestion\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAvoids\u0026thinsp;~\u0026thinsp;0.27 tCO₂e/tonne waste; adds\u0026thinsp;~\u0026thinsp;0.1 tCO₂e to soils\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eHigh potential due to heavy reliance on open dumping\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eBernstad \u0026amp; la Cour Jansen (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2012\u003c/span\u003e); Boldrin et al. (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2009\u003c/span\u003e); Ike et al. (\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2018\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWater Facilities\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eConstructed wetlands\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e100\u0026ndash;200 g C/m\u0026sup2;/year\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRelevant for flooding control and sanitation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRetta et al. (\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2023\u003c/span\u003e); Brix \u0026amp; Arias (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2005\u003c/span\u003e); Muhoza \u0026amp; Zhou (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2024\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eSource: Author\u0026rsquo;s Compilation, 20205.\u003c/b\u003e \u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e highlighted the comparative carbon sequestration potential of different urban facilities and their contextual relevance to Benin Metropolis. Green infrastructure comprising trees, parks, and green roofs shows strong capacity for both direct carbon capture and multiple co-benefits such as heat reduction and flood mitigation. Mature urban trees can sequester 20\u0026ndash;50 kg of CO₂ annually, while green roofs contribute an additional 0.5\u0026ndash;2.5 kg CO₂ per square metre per year. However, the potential of these interventions in Benin Metropolis is constrained by challenges such as competition for land, weak institutional frameworks, and poor maintenance culture, which limit sustainability despite high ecological benefits.\u003c/p\u003e \u003cp\u003eIn the building sector, interventions such as mass timber construction, bio-based materials, and retrofitting stand out for their ability to reduce embodied carbon by over 60%, with timber structures capable of storing 500\u0026ndash;700 kg of CO₂ per square metre. This presents a particularly strong opportunity for Benin Metropolis given the availability of forest resources in Edo State. Nevertheless, outdated building codes, weak governance mechanisms, and societal perceptions of timber as inferior to concrete create significant barriers that must be addressed through reforms and awareness campaigns.\u003c/p\u003e \u003cp\u003eTransportation facilities offer indirect sequestration benefits by reducing emissions through electrification, mass transit, and active mobility systems. The estimated 30\u0026ndash;50% reduction in emissions underscores their importance for long-term decarbonisation. For Benin Metropolis, these interventions are feasible but would require investment in pilot electric vehicle fleets, expansion of public transit systems, and infrastructure for walking and cycling.\u003c/p\u003e \u003cp\u003eWaste facilities emerge as one of the most immediately actionable areas for intervention. Composting and anaerobic digestion not only prevent the release of methane a highly potent greenhouse gas but also enhance soil carbon sequestration, avoiding about 0.27 tonnes of CO₂-equivalent per tonne of organic waste and adding approximately 0.1 tonnes to soils. Given Benin Metropolis\u0026rsquo;s reliance on open dumping, this pathway holds high potential for both climate and public health benefits.\u003c/p\u003e \u003cp\u003eFinally, water facilities such as constructed wetlands demonstrate moderate but significant carbon sequestration capacity, storing 100\u0026ndash;200 grams of carbon per square metre annually. Their relevance in Benin Metropolis lies not only in carbon capture but also in their ability to address flooding and sanitation challenges, which are pressing urban issues. See Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e for the Comparative Carbon Sequestration Potential by Facilities Type in Benin Metropolis.\u003c/p\u003e \u003cp\u003eThe results from Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e showed a striking disparity between categories, highlighting the relative magnitude of each intervention\u0026rsquo;s impact. Buildings stand out as the most impactful sector, with an estimated sequestration or emission reduction potential of about 600 scaled units. This dominance reflects the substantial benefits of adopting mass timber construction, retrofits, and bio-based materials, which can lock carbon in structural components while simultaneously reducing embodied emissions.\u003c/p\u003e \u003cp\u003eIn contrast, transport (40) and green infrastructure (35) each demonstrated a more modest but still a meaningful contribution, averaging around 40 scaled units. In green infrastructure, urban trees, parks, and green roofs sequester carbon directly while offering critical co-benefits such as urban cooling, flood control, and biodiversity enhancement. Transport interventions, on the other hand, primarily reduce emissions indirectly through electrification, mass transit, and active mobility systems. Their relatively similar contribution to green infrastructure highlights the shared role of both sectors as medium-impact strategies that require supportive policies and investment for effective implementation.\u003c/p\u003e \u003cp\u003eWaste and water facilities rank the lowest in terms of direct carbon sequestration potential, with 0.27 and 0.15 scaled units respectively. Despite their smaller numerical contribution, these interventions should not be underestimated. Composting, anaerobic digestion, and constructed wetlands not only provide carbon benefits but also address urgent challenges in Benin Metropolis such as poor sanitation, flooding, and methane emissions from unmanaged waste. Their value lies in multifunctionality delivering ecosystem and health benefits alongside modest carbon gains.\u003c/p\u003e \u003cp\u003eHence, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e highlighted a critical insight: while buildings offer the greatest single opportunity for carbon sequestration, Benin Metropolis cannot rely on one facility type alone. Instead, a diversified strategy is needed, where green infrastructure, transport, and waste-water systems complement building interventions. Together, these pathways form an integrated framework that balances high carbon storage with immediate co-benefits for urban resilience and sustainability.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec31\" class=\"Section2\"\u003e \u003ch2\u003e5.7 Key Cross-Cutting Findings\u003c/h2\u003e \u003cp\u003eSeveral broader insights emerged: first, interventions that generate immediate co-benefits such as reduced flooding, heat mitigation, and improved sanitation are more likely to gain traction. Second, socio-institutional barriers, including governance fragmentation, financing gaps, and limited technical expertise, outweigh technical challenges in constraining implementation. Third, sustained community engagement is indispensable to ensure long-term maintenance and acceptance. Finally, medium-sized cities like Benin, while resource-constrained, retain flexibility to experiment and innovate since they are less entrenched in carbon-heavy infrastructures.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec32\" class=\"Section2\"\u003e \u003ch2\u003e5.8 Implications for Benin Metropolis\u003c/h2\u003e \u003cp\u003eFor Benin Metropolis, the findings underscore that green infrastructure and decentralised waste management represent the most immediately actionable strategies, combining strong sequestration potential with urgent co-benefits. Mass timber and other bio-based building strategies hold medium- to long-term promise but will require regulatory reforms, investment in local supply chains, and cultural acceptance. Transport interventions, particularly electrification and transit upgrades, are essential to curb future emissions. Constructed wetlands offer a multifunctional solution, addressing flooding and sanitation while providing modest sequestration benefits.\u003c/p\u003e \u003cp\u003eTaken together, the results provide a robust empirical foundation for the integrative framework developed in later sections. They demonstrate that transforming Benin Metropolis\u0026rsquo;s facilities into carbon sinks is feasible, but success will depend on governance reforms, community participation, and long-term policy commitment.\u003c/p\u003e \u003c/div\u003e"},{"header":"6. Discussion of Results","content":"\u003cp\u003eThe results of this study revealed that integrating carbon sequestration into urban facility planning is both feasible and potentially transformative for metropolitan area like Benin. The findings revealed that interventions such as urban greening, carbon-negative construction, sustainable transportation, waste-to-resource systems, and constructed wetlands are effective in reducing emissions and enhancing carbon sinks. Yet, the deeper significance of these findings emerges when they are interpreted through the lenses of \u003cem\u003eUrban Political Ecology (UPE), the Circular Bioeconomy, and Sustainable Urban Development Theory\u003c/em\u003e. The discussion that follows critically situates the findings within these theoretical frames, while also considering practical challenges, governance dynamics, and the lived realities of Benin Metropolis.\u003c/p\u003e \u003cdiv id=\"Sec34\" class=\"Section2\"\u003e \u003ch2\u003e6.1 Linking Results to Urban Political Ecology\u003c/h2\u003e \u003cp\u003eUrban Political Ecology highlights how power, inequality, and governance shape environmental outcomes. The findings confirm that socio-political barriers, more than technological constraints, determine the success of carbon sequestration strategies. For example, while green infrastructure has clear carbon and co-benefits, its deployment in Benin Metropolis is hampered by competing land uses, weak enforcement of planning laws, and limited budget allocations. These challenges reflect deeper political choices about what is prioritised in urban development: short-term revenue from real estate expansion versus long-term ecological sustainability.\u003c/p\u003e \u003cp\u003eSimilarly, waste management in Benin Metropolis illustrates UPE\u0026rsquo;s claim that environmental crises are socially produced. The reliance on open dumps is not inevitable but results from governance failures, insufficient investment, and marginalisation of informal recyclers. The findings that decentralised composting and anaerobic digestion could cut emissions highlight the lost opportunities embedded in current power arrangements. Unless the city deliberately integrates informal actors into formal systems, carbon-saving strategies risk reproducing inequalities by excluding those who already contribute to recycling under precarious conditions.\u003c/p\u003e \u003cp\u003eIn transport, UPE underscores that transitions to electric mobility are not simply technical shifts but political-economic projects requiring subsidies, infrastructure, and regulatory reform. If poorly managed, they could widen inequalities benefiting wealthier commuters who can afford electric cars while leaving poorer residents reliant on polluting minibuses. Thus, the results confirm that carbon gains in Benin Metropolis must be evaluated through questions of justice: \u003cem\u003eWho benefits? Who pays? Who is left behind?\u003c/em\u003e\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec35\" class=\"Section2\"\u003e \u003ch2\u003e6.2 Interpreting Results through the Circular Bioeconomy\u003c/h2\u003e \u003cp\u003eThe Circular Bioeconomy provides a complementary lens, focusing on efficiency and regeneration. The findings strongly resonate with this paradigm. Waste facilities, for instance, illustrate how organic matter can be transformed from a methane source into a carbon sink and resource for compost or energy. Similarly, the adoption of mass timber and bamboo aligns with the circular principle of substituting finite, carbon-intensive materials with renewable, carbon-storing ones.\u003c/p\u003e \u003cp\u003eThe results also underscore the importance of local resource cycles. Edo State\u0026rsquo;s forests present opportunities for a timber-based construction economy, but only if harvesting is managed sustainably. Without strong regulatory oversight, the risk of deforestation could outweigh carbon benefits. This reflects a central tension in the bioeconomy: balancing utilisation with regeneration. For Benin Metropolis, this means designing closed-loop systems where waste is recycled locally, water is purified through wetlands, and building materials are sourced responsibly.\u003c/p\u003e \u003cp\u003eCrucially, the circular bioeconomy reframes sustainability as an opportunity rather than a burden. By showing that compost can improve soils, biogas can provide affordable energy, and timber construction can create jobs, the findings position carbon sequestration as a driver of green livelihoods. This perspective is particularly important in Nigeria, where unemployment and poverty remain pressing challenges.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec36\" class=\"Section2\"\u003e \u003ch2\u003e6.3 Situating Results in Sustainable Urban Development Theory\u003c/h2\u003e \u003cp\u003eThe third theoretical pillar, Sustainable Urban Development Theory, provides the normative foundation for interpreting results. The findings affirm that sustainability is not a luxury but a necessity. Benin Metropolis\u0026rsquo;s unplanned growth has already exacerbated flooding, heat stress, and waste crises. The evidence that constructed wetlands and urban forests can mitigate these risks demonstrates that carbon sequestration strategies are simultaneously adaptation and mitigation measures.\u003c/p\u003e \u003cp\u003eSustainable urbanism also highlights the importance of long-term integration. The results indicate that while transport electrification and timber construction require significant upfront investment, their long-term benefits justify inclusion in planning frameworks. Cities that fail to embed such strategies early risk being locked into carbon-intensive trajectories. For Benin, the urgency is clear: with its population projected to expand, the choices made now will determine whether it becomes a sustainable, carbon-conscious city or entrenches unsustainable growth.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec37\" class=\"Section2\"\u003e \u003ch2\u003e6.4 Governance and Institutional Implications\u003c/h2\u003e \u003cp\u003eA cross-cutting theme in the findings is the centrality of governance. Whether in tree planting, building codes, or waste management, institutional weakness undermines implementation. For instance, evidence from Accra and Nairobi shows that tree planting initiatives often fail due to lack of maintenance. Benin risks repeating these failures unless governance structures ensure continuity.\u003c/p\u003e \u003cp\u003eThe findings also highlight opportunities for decentralised governance. Community-driven projects such as neighbourhood composting or local greening tend to be more sustainable than top-down initiatives. This suggests that Benin should adopt a multi-level governance model, combining state-level policy with community empowerment. International experience shows that polycentric governance, where multiple actors share responsibility, fosters innovation and accountability (Ostrom, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2010\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec38\" class=\"Section2\"\u003e \u003ch2\u003e6.5 Social Justice and Equity Considerations\u003c/h2\u003e \u003cp\u003eThe results raise critical issues of equity. Urban Political Ecology reminds us that carbon sequestration projects can inadvertently reproduce exclusion. For example, creating new parks or wetlands could displace informal settlers. Electrification of transport may privilege wealthier groups. Even tree planting may reinforce inequalities if maintenance is left to communities lacking resources.\u003c/p\u003e \u003cp\u003eTherefore, strategies must be designed inclusively. Evidence from African cities shows that when communities are engaged in co-designing and co-managing facilities, projects achieve greater legitimacy and durability. For Benin, this means integrating informal waste pickers, market women, and neighbourhood associations into planning processes. Without such inclusion, carbon sequestration risks becoming another elite-driven agenda disconnected from urban realities.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec39\" class=\"Section2\"\u003e \u003ch2\u003e6.6 Lessons from Global and Regional Comparisons\u003c/h2\u003e \u003cp\u003eThe comparative evidence provides several lessons for Benin Metropolis. From Europe and North America, the adoption of mass timber shows the feasibility of scaling carbon-storing buildings, but it also highlights the need for updated codes and training. From Asian cities, constructed wetlands demonstrate cost-effective water management solutions suitable for tropical climates. From Lagos, the BRT system underscores the importance of investing in mass transit even amid governance challenges. From Kigali, electric motorcycles show that innovation is possible even in resource-constrained contexts.\u003c/p\u003e \u003cp\u003eAt the same time, the African cases caution against overreliance on imported models. Projects must be tailored to local realities. For instance, Benin cannot simply replicate Lagos\u0026rsquo; BRT without addressing its different urban morphology and population density. Instead, the lesson is to adapt principles\u0026mdash;mass transit, electrification, green spaces into context-specific designs.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec40\" class=\"Section2\"\u003e \u003ch2\u003e6.7 Practical Implications for Benin Metropolis\u003c/h2\u003e \u003cp\u003eFor Benin Metropolis, the findings suggest a hierarchy of priorities. Green infrastructure and waste management should be immediate priorities, as they deliver both carbon and urgent co-benefits such as flood control and sanitation. Transport and building reforms represent medium- to long-term goals requiring policy shifts and investments. Constructed wetlands can be integrated into ongoing drainage projects, providing a cost-effective dual solution.\u003c/p\u003e \u003cp\u003eThese priorities align with Nigeria\u0026rsquo;s Climate Change Act (2021), which mandates carbon budgeting. By embedding sequestration into the city\u0026rsquo;s Master Plan, Benin can position itself as a pioneer among Nigerian cities in operationalising the Act at a subnational level. Partnerships with universities, civil society, and international donors can provide technical and financial support.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec41\" class=\"Section2\"\u003e \u003ch2\u003e6.8 The Human Dimension: Why This Matters\u003c/h2\u003e \u003cp\u003eBeyond technical details, the findings speak to a deeper human story. Benin Metropolis is already experiencing the brunt of climate change flooded streets, unbearable heat, unmanaged waste. These realities affect livelihoods, health, and dignity. The evidence that trees can cool neighbourhoods, compost can improve soils, and wetlands can reduce flooding is not abstract; it is about making the city more liveable for its people.\u003c/p\u003e \u003cp\u003eCarbon sequestration, therefore, should not be seen as a distant global agenda but as a local pathway to restoring balance between people and their environment. This human dimension gives the findings moral urgency: the future of Benin depends not just on emission reductions but on re-imagining the city as a living carbon sink that sustains both people and planet.\u003c/p\u003e \u003cp\u003e \u003cb\u003e6.9 Summary of Key Insights\u003c/b\u003e \u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eCarbon sequestration is technically feasible across multiple facility types in Benin Metropolis.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe main obstacles are governance, institutional capacity, and social inclusion, rather than technology.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eGreen infrastructure and waste management offer the most immediate gains; transport and buildings provide medium- to long-term opportunities.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eSuccess requires integration of technical, political, and social dimensions, consistent with the study\u0026rsquo;s theoretical framework.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe ultimate significance lies in the human benefits\u0026mdash;cooler, cleaner, healthier, and more resilient urban spaces.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003e7. Policy Implications\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe findings of this study underscore that the integration of carbon sequestration into urban facility planning is both urgent and feasible for Benin Metropolis. Yet, translating these opportunities into real outcomes requires deliberate policy interventions. The following section outlines the policy implications at the \u003cb\u003el\u003c/b\u003e\u003cem\u003eocal, state, national, and international levels\u003c/em\u003e, drawing connections between technical strategies, governance reforms, and broader development agendas.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec42\" class=\"Section2\"\u003e \u003ch2\u003e7.1 Embedding Carbon Sequestration into Urban Planning Frameworks\u003c/h2\u003e \u003cp\u003eThe most immediate implication is the need to embed carbon sequestration into Benin Metropolis\u0026rsquo;s Master Plan and related urban development policies. At present, most Nigerian urban plans prioritise housing, transport, and economic growth without explicitly addressing carbon sinks. This omission risks locking the city into unsustainable trajectories. Integrating carbon goals requires mandating \u003cem\u003egreen infrastructure corridors, tree-lined streets, wetlands in flood-prone areas, and the use of carbon-negative materials\u003c/em\u003e in public projects.\u003c/p\u003e \u003cp\u003eSuch integration should not be symbolic. Planning codes must include measurable carbon targets, ensuring that every new facility contributes to climate mitigation. For example, planning approvals could require developers to demonstrate how buildings or estates will sequester or offset carbon, whether through green roofs, bio-based construction, or urban forestry contributions. By embedding sequestration into the regulatory DNA of planning, Benin can institutionalise sustainability rather than treating it as an afterthought.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec43\" class=\"Section2\"\u003e \u003ch2\u003e7.2 Updating Building Codes and Standards\u003c/h2\u003e \u003cp\u003eThe findings show that mass timber, bamboo, and other bio-based materials significantly reduce embodied carbon. However, outdated building codes in Nigeria often restrict their use. A key policy implication is therefore the \u003cem\u003eurgent revision of building codes\u003c/em\u003e to recognise and regulate carbon-negative materials. This should be accompanied by training programmes for architects, engineers, and builders to build technical capacity and public confidence.\u003c/p\u003e \u003cp\u003eGovernment-led demonstration projects such as constructing schools, health centres, or administrative buildings with mass timber could serve as proof of concept, shifting cultural perceptions of timber as \u0026ldquo;inferior\u0026rdquo; to concrete. Edo State, with its timber resources, could lead this transition, provided sustainable forest management policies prevent overharvesting.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec44\" class=\"Section2\"\u003e \u003ch2\u003e7.3 Strengthening Waste Management Policies\u003c/h2\u003e \u003cp\u003eThe results revealed that waste management offers one of the most immediate carbon-saving opportunities. Yet, Benin Metropolis currently relies on open dumping, with minimal waste segregation. Policy implications include:\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eMandatory waste segregation at source\u003c/b\u003e for households, markets, and institutions, supported by public awareness campaigns.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eDecentralised composting and biogas plants\u003c/b\u003e integrated into neighbourhoods, turning organic waste into resources.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eFormal recognition of informal waste pickers\u003c/b\u003e, offering them training, protective equipment, and integration into municipal waste systems.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eIncentives for recycling industries\u003c/b\u003e, including tax breaks and access to microfinance.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003eBy shifting from a disposal mindset to a resource recovery model, Benin can cut methane emissions, enhance soil carbon, and create green jobs, aligning with circular bioeconomy principles.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec45\" class=\"Section2\"\u003e \u003ch2\u003e7.4 Advancing Sustainable Mobility Policies\u003c/h2\u003e \u003cp\u003eTransport policies are critical to reducing Benin Metropolis\u0026rsquo;s emissions. The results suggest that electrifying minibuses and introducing mass transit could drastically reduce reliance on fossil fuels. Policy implications include:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eEstablishing an \u003cem\u003eElectric Vehicle (EV) Roadmap\u003c/em\u003e for the city, starting with pilot fleets of electric buses or minibuses.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eProviding \u003cem\u003echarging infrastructure\u003c/em\u003e at key transport hubs.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eOffering \u003cem\u003etax incentives or subsidies\u003c/em\u003e for private adoption of electric motorcycles and cars.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eExpanding \u003cem\u003enon-motorised transport infrastructure\u003c/em\u003e, including sidewalks and cycling lanes, to encourage behavioural shifts.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eThese policies should be phased to match the city\u0026rsquo;s resource capacity, beginning with pilot projects before scaling citywide. Importantly, they must be designed inclusively to avoid privileging elites while leaving the majority reliant on polluting systems.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec46\" class=\"Section2\"\u003e \u003ch2\u003e7.5 Integrating Constructed Wetlands into Drainage Policy\u003c/h2\u003e \u003cp\u003eFlooding is a recurrent problem in Benin Metropolis, exacerbated by climate change and unregulated construction. The results highlight constructed wetlands as cost-effective facilities that sequester carbon while improving drainage and water quality. Policy implications include mandating wetlands in new drainage and wastewater projects, particularly in flood-prone areas such as Upper Sakponba and Ugbowo.\u003c/p\u003e \u003cp\u003eSuch wetlands should be protected through zoning policies that prevent encroachment. Partnerships with universities and NGOs could ensure scientific monitoring, while community groups could be engaged for maintenance. This dual approach technical and social would ensure wetlands function as resilient, carbon-storing infrastructure.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec47\" class=\"Section2\"\u003e \u003ch2\u003e7.6 Financing Carbon-Sequestering Infrastructure\u003c/h2\u003e \u003cp\u003eFinancing emerged as a recurring challenge in the results. Many interventions require upfront investment even if they produce long-term savings. Policy responses must therefore mobilise diverse funding sources:\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eClimate Finance\u003c/b\u003e: Benin Metropolis can access international funds such as the Green Climate Fund and the Global Environment Facility by aligning projects with Nigeria\u0026rsquo;s Nationally Determined Contributions (NDCs).\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003ePublic-Private Partnerships (PPPs)\u003c/b\u003e: Private developers can be incentivised to invest in green infrastructure through land concessions, tax breaks, or co-financing schemes.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eCarbon Markets\u003c/b\u003e: By quantifying and verifying carbon gains, Benin could participate in voluntary carbon markets, generating revenue from sequestration projects.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eLocal Green Bonds\u003c/b\u003e: Edo State could issue municipal green bonds to finance carbon-sequestering projects, tapping into domestic investors seeking sustainable portfolios.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003eWithout innovative financing mechanisms, even the most technically sound policies will remain aspirational.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec48\" class=\"Section2\"\u003e \u003ch2\u003e7.7 Institutional and Governance Reforms\u003c/h2\u003e \u003cp\u003eThe results emphasised governance fragmentation as a major barrier. Policy implications include clarifying institutional mandates for carbon governance. Currently, responsibilities are dispersed across ministries and agencies, leading to duplication or neglect. Benin Metropolis would benefit from establishing a \u003cem\u003eClimate and Carbon Office\u003c/em\u003e within the local government, tasked with coordinating sequestration initiatives, monitoring carbon budgets, and liaising with state and federal agencies.\u003c/p\u003e \u003cp\u003eFurthermore, polycentric governance where state, local, and community actors share responsibility should be institutionalised. For example, while the local government could oversee citywide planning, neighbourhood associations could manage local greening and composting projects. Such shared governance increases accountability and resilience.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec49\" class=\"Section2\"\u003e \u003ch2\u003e7.8 Community Participation as Policy Priority\u003c/h2\u003e \u003cp\u003eThe results showed that projects thrive when communities are actively engaged. Policy must therefore institutionalise participation. This could involve:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eEstablishing \u003cem\u003eneighbourhood green committees\u003c/em\u003e responsible for local tree planting and park maintenance.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eProviding micro-grants for community-led composting or wetland projects.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eIncluding informal workers in official waste and recycling systems.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eEmbedding participatory budgeting, allowing communities to allocate part of the climate budget to local priorities.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eBy grounding policies in community agency, carbon sequestration becomes not an imposed agenda but a shared responsibility.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec50\" class=\"Section2\"\u003e \u003ch2\u003e7.9 Alignment with National and Global Agendas\u003c/h2\u003e \u003cp\u003eLocal policies must align with broader frameworks. Nigeria\u0026rsquo;s Climate Change Act (2021) requires carbon budgeting and mainstreaming climate action across sectors. Benin Metropolis can operationalise the Act at the municipal level, setting a precedent for other Nigerian cities. Policies should also align with \u003cem\u003eSustainable Development Goal 11 (Sustainable Cities and Communities) and SDG 13 (Climate Action)\u003c/em\u003e, ensuring coherence with international commitments.\u003c/p\u003e \u003cp\u003eAt the global level, demonstrating progress could attract international partnerships and financing. Benin\u0026rsquo;s integration of carbon sequestration into urban facilities would not only meet local needs but also contribute to Nigeria\u0026rsquo;s NDCs under the Paris Agreement.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec51\" class=\"Section2\"\u003e \u003ch2\u003e7.10 Risks of Inaction\u003c/h2\u003e \u003cp\u003eFinally, the policy implications are sharpened when contrasted with the risks of inaction. Without embedding carbon sequestration into planning, Benin Metropolis faces worsening floods, heat stress, air pollution, and waste crises. These risks carry significant economic costs in lost productivity, damaged infrastructure, and healthcare burdens. Conversely, proactive policies can transform these risks into opportunities\u0026mdash;creating jobs, improving health, and enhancing resilience while contributing to global climate goals.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec52\" class=\"Section2\"\u003e \u003ch2\u003e7.11 Summary of Policy Pathways\u003c/h2\u003e \u003cp\u003eThe discussion above can be summarised into five policy pathways for Benin Metropolis:\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eInstitutionalising carbon goals\u003c/b\u003e in urban planning and building codes.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eReforming waste and water systems\u003c/b\u003e into circular, carbon-sequestering infrastructures.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003ePromoting sustainable transport\u003c/b\u003e, beginning with pilots in electrification and non-motorised mobility.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eMobilising finance\u003c/b\u003e through climate funds, PPPs, carbon markets, and green bonds.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eStrengthening governance and participation\u003c/b\u003e, ensuring inclusive and accountable implementation.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003e8. Recommendations\u003c/b\u003e \u003c/p\u003e \u003cp\u003eTo operationalise the findings of this study, it is essential that carbon sequestration be embedded into the very foundations of urban planning in Benin Metropolis. The city\u0026rsquo;s Master Plan should be updated to include explicit carbon targets, ensuring that every new development contributes to climate mitigation. Developers ought to be required to integrate sequestration measures such as tree planting, green roofs, or the use of bio-based construction materials into their projects. Such policy adjustments will institutionalise sustainability, making it a standard rather than an exception.\u003c/p\u003e \u003cp\u003eReforming building codes is another priority. Nigeria\u0026rsquo;s existing codes largely restrict the use of mass timber, bamboo, and other carbon-negative materials, thereby reinforcing dependence on carbon-intensive concrete and steel. Revising these codes to recognise sustainable alternatives, alongside government-led demonstration projects, would showcase the viability and attractiveness of timber and bamboo buildings. This would not only reduce embodied carbon but also shift public perceptions of these materials from \u0026ldquo;inferior\u0026rdquo; to modern, durable, and climate-friendly solutions.\u003c/p\u003e \u003cp\u003eWaste management also requires urgent transformation. Policies mandating household and institutional waste segregation should be introduced and supported by citywide awareness campaigns. Decentralised composting centres and anaerobic digestion facilities can convert organic waste into useful products such as compost and biogas, cutting methane emissions while creating livelihoods. Crucially, informal waste workers, who already play a central role in recycling, must be formally recognised and integrated into the municipal system, with training, equipment, and fair compensation provided to enhance their contributions.\u003c/p\u003e \u003cp\u003eIn the transport sector, a phased transition to low-carbon systems should be pursued. Pilot projects introducing electric minibuses, coupled with the development of charging infrastructure at transport hubs, would mark a significant step toward decarbonisation. At the same time, expanding pedestrian walkways and cycling lanes will make non-motorised mobility safer and more attractive, reducing short car trips. Policies should also provide subsidies or incentives for the gradual adoption of electric motorcycles, which are already popular in Benin Metropolis and could serve as an entry point for wider electrification.\u003c/p\u003e \u003cp\u003eWater management must equally be reconceptualised. Constructed wetlands should be integrated into flood-prone zones as part of both drainage and wastewater systems. Beyond carbon sequestration, such wetlands would alleviate flooding, purify water, and create biodiversity corridors. Strong zoning policies will be required to protect these wetlands from encroachment, while community groups could be engaged in their upkeep to ensure long-term functionality and ownership.\u003c/p\u003e \u003cp\u003eNone of these interventions will be possible without financing and governance reforms. Benin Metropolis should actively pursue international climate finance opportunities, particularly through alignment with Nigeria\u0026rsquo;s Climate Change Act and its commitments under the Paris Agreement. Local financing options such as municipal green bonds and public\u0026ndash;private partnerships must also be explored to mobilise resources. To coordinate efforts, a Climate and Carbon Office within the city government should be established, tasked with monitoring progress, enforcing carbon targets, and fostering collaboration across sectors.\u003c/p\u003e \u003cp\u003eFinally, policies must prioritise community engagement. Urban residents are not passive beneficiaries but active stakeholders whose participation is essential for success. Participatory planning and budgeting should be institutionalised, enabling residents to shape local greening, composting, and wetland projects. Micro-grants for neighbourhood associations can stimulate grassroots innovation, while recognition of informal actors ensures inclusivity. By embedding participation at every stage, carbon sequestration will not only mitigate climate change but also strengthen trust, ownership, and collective responsibility across the city.\u003c/p\u003e \u003c/div\u003e"},{"header":"9. Final Reflection","content":"\u003cp\u003eThe evidence makes it clear that carbon sequestration in Benin Metropolis is not an abstract, distant goal but an urgent and achievable pathway to sustainability. Trees, timber, compost, wetlands, and electric mobility are not simply technical solutions; they are tools for reimagining the city as a place that restores rather than depletes. The challenge is not whether Benin can do this, but whether the political will, institutional reforms, and community partnerships can be mobilised quickly enough. If pursued decisively, the metropolitan area could emerge as a model for medium-sized African cities grappling with climate change. By embedding carbon sequestration at the heart of its planning agenda, Benin Metropolis has the chance to create not just a more sustainable urban environment but a more just, liveable, and resilient home for its people.\u003c/p\u003e"},{"header":"10. Conclusion","content":"\u003cp\u003eThis study has demonstrated the significant potential of embedding carbon sequestration into the planning and management of urban facilities in Benin Metropolis, Nigeria. Drawing on a systematic review and meta-analysis of global, regional, and Nigerian evidence, it showed that facilities such as green infrastructure, buildings, transport, waste systems, and constructed wetlands can be reimagined to operate not only as service providers but also as active carbon sinks. The comparative impact assessment (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) revealed that \u003cem\u003egreen infrastructure and building\u003c/em\u003e rank as the most immediately actionable interventions, offering relatively low-cost, socially inclusive solutions with urgent co-benefits such as reduced flooding, improved sanitation, and enhanced thermal comfort. In contrast, \u003cem\u003ewaste management and transport systems\u003c/em\u003e hold strong medium- to long-term potential, particularly through mass timber, bio-based materials, and electrified mass transit, though these require significant policy reforms and infrastructural investment. \u003cem\u003eConstructed wetlands\u003c/em\u003e, while modest in direct carbon gains, provide multifunctional benefits, particularly in flood management and sanitation, making them vital supporting interventions.\u003c/p\u003e \u003cp\u003eTheoretically, the study advances a triadic framework combining Urban Political Ecology, the Circular Bioeconomy, and Sustainable Urban Development Theory. This synthesis underscores that carbon sequestration is not a purely technical matter but a multidimensional urban project. It involves addressing socio-political questions of governance and justice, operationalising regenerative material and ecological cycles, and embedding sustainability principles into long-term urban growth trajectories.\u003c/p\u003e \u003cp\u003eFor Benin Metropolis, the findings highlight both opportunity and challenge. The city\u0026rsquo;s ecological endowment, its proximity to Edo State\u0026rsquo;s forests, and its dynamic population growth provide fertile ground for innovation. Yet persistent governance weaknesses, fragmented planning, and limited financial capacity remain critical barriers. To address these, a staged approach is essential:\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eShort-term (0\u0026ndash;5 years)\u003c/strong\u003e \u003cp\u003ePrioritise community-driven tree planting, reforestation of degraded areas, decentralised composting, and pilot waste-to-energy initiatives.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eMedium-term (5\u0026ndash;15 years)\u003c/strong\u003e \u003cp\u003eIntegrate mass timber and bio-based materials into public building projects, establish electric bus pilots, and adopt policies incentivising green roofs and active transport infrastructure.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eLong-term (15\u0026thinsp;+\u0026thinsp;years)\u003c/strong\u003e \u003cp\u003eMainstream constructed wetlands into the city\u0026rsquo;s water and flood management systems, scale up sustainable building supply chains, and embed carbon sequestration principles into the city\u0026rsquo;s master planning and land-use frameworks.\u003c/p\u003e \u003c/p\u003e \u003cp\u003eGenerally, carbon sequestration must move from the margins to the centre of urban policy and facility planning in Benin Metropolis. By positioning it as a core organising principle, the city can simultaneously confront climate change, address socio-economic inequalities, and strengthen resilience against environmental risks. Conversely, failure to adopt this integrated, staged approach risks deepening ecological degradation and exacerbating urban challenges.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eConsent to Publish Declaration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot Applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Participate Declaration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot Applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics Declaration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot Applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClinical Trial Number\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot Applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot Applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClinical Trial Number\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot Applicable\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAdebayo A, Omoniyi S. Urban green spaces and climate change mitigation in Nigeria: Potentials and challenges. J Environ Planning Manage. 2019;62(5):785\u0026ndash;803. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1080/09640568.2018.1470962\u003c/span\u003e\u003cspan address=\"10.1080/09640568.2018.1470962\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAdegun OB, Ikudayisi EA, Morakinyo TE. Urban green infrastructure in Nigeria: A review. Sci Afr. 2021;14:e01044. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.sciaf.2021.e01044\u003c/span\u003e\u003cspan address=\"10.1016/j.sciaf.2021.e01044\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAhmed S, Arocho I. Mass timber building material in the U.S. construction industry: Determining the existing awareness level, construction-related challenges, and recommendations to increase its current acceptance level. Clean Eng Technol. 2020;1:100007. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/S2666790820300070\u003c/span\u003e\u003cspan address=\"10.1016/S2666790820300070\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAlabi MO. Sustainable urban form and challenges of open space utilization, Akure, Nigeria as a case study. Int J Urban Sustainable Dev. 2020;12(1). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1080/19463138.2020.1728691\u003c/span\u003e\u003cspan address=\"10.1080/19463138.2020.1728691\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAtedhor GO. Nigeria\u0026rsquo;s climate responsiveness: Navigating energy-climate and techno-financial conundrums in the low-carbon energy transition. Energy Sustain Dev. 2025;88:101810. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.esd.2025.101810\u003c/span\u003e\u003cspan address=\"10.1016/j.esd.2025.101810\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBar\u0026oacute; F, Chaparro L, G\u0026oacute;mez-Baggethun E, Langemeyer J, Nowak DJ, Terradas J. Contribution of ecosystem services to air quality and climate change mitigation policies: The case of urban forests in Barcelona, Spain. Ambio. 2014;43(4):466\u0026ndash;79. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s13280-014-0507-x\u003c/span\u003e\u003cspan address=\"10.1007/s13280-014-0507-x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBernstad A, la Cour Jansen J. Review of comparative LCAs of food waste management systems: Current status and potential improvements. Waste Manag. 2012;32(12):2439\u0026ndash;55. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.wasman.2012.07.023\u003c/span\u003e\u003cspan address=\"10.1016/j.wasman.2012.07.023\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBoldrin A, Andersen JK, M\u0026oslash;ller J, Christensen TH, Favoino E. Composting and compost utilization: Accounting of greenhouse gases and global warming contributions. Waste Manage Res. 2009;27(8):800\u0026ndash;12. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1177/0734242X09345275\u003c/span\u003e\u003cspan address=\"10.1177/0734242X09345275\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBrix H, Arias CA. The use of vertical flow constructed wetlands for on-site treatment of domestic wastewater: New Danish guidelines. Ecol Eng. 2005;25(5):491\u0026ndash;500. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ecoleng.2005.07.009\u003c/span\u003e\u003cspan address=\"10.1016/j.ecoleng.2005.07.009\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCai J, Zhao Z, Zhou Z, Wang Y. Predicting the carbon emission reduction potential of shared electric bicycle travel. Transp Res Part D: Transp Environ. 2024;129:104107. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.trd.2024.104107\u003c/span\u003e\u003cspan address=\"10.1016/j.trd.2024.104107\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCampbell S. Green cities, growing cities, just cities? Urban planning and the contradictions of sustainable development. J Am Plann Association. 1996;62(3):296\u0026ndash;312. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1080/01944369608975696\u003c/span\u003e\u003cspan address=\"10.1080/01944369608975696\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCervero R. (2000). \u003cem\u003eInformal Transport in the Developing World\u003c/em\u003e. UN-Habitat. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://unhabitat.org/sites/default/files/download-manager-files/Informal%20Transport%20in%20the%20Developing%20World.pdf\u003c/span\u003e\u003cspan address=\"https://unhabitat.org/sites/default/files/download-manager-files/Informal%20Transport%20in%20the%20Developing%20World.pdf\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChima WO. Innovative approaches to sustainable building practices in Nigeria: Advancing green construction through local materials and technological integration: A case study of Abuja Municipal Area Council (AMAC). Int J Latest Technol Eng Manage Appl Sci. 2025;14(6):783\u0026ndash;90. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.51583/IJLTEMAS.2025.140600085\u003c/span\u003e\u003cspan address=\"10.51583/IJLTEMAS.2025.140600085\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChurkina G, Organschi A, Reyer CPO, Ruff A, Vinke K, Liu Z, Reck BK, Graedel TE, Schellnhuber HJ. Buildings as a global carbon sink. Nat Sustain. 2020;3(4):269\u0026ndash;76. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1038/s41893-019-0462-4\u003c/span\u003e\u003cspan address=\"10.1038/s41893-019-0462-4\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCobbinah PB, Niminga-Beka R. Urban planning and climate change in Africa: Experiences from Ghana. Habitat Int. 2017;69:49\u0026ndash;58. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.habitatint.2017.09.009\u003c/span\u003e\u003cspan address=\"10.1016/j.habitatint.2017.09.009\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCreutzig F, Jochem P, Edelenbosch OY, Mattauch L, van Vuuren DP, McCollum D, Minx J, Transport. A roadblock to climate change mitigation? Science, 350 (6263), 911\u0026ndash;2. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.science.org/doi/\u003c/span\u003e\u003cspan address=\"https://www.science.org/doi/\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1126/science.aac8033\u003c/span\u003e\u003cspan address=\"10.1126/science.aac8033\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDipeolu AA. Determinants of residents\u0026rsquo; preferences for urban green infrastructures. Urban Forestry Urban Green. 2021;60., Article 127072. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ufug.2020.127072\u003c/span\u003e\u003cspan address=\"10.1016/j.ufug.2020.127072\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003edu Toit MJ, Cilliers SS, Dallimer M, Goddard M, Guenat S, Cornelius SF. Urban green infrastructure and ecosystem services in sub-Saharan Africa. Landsc Urban Plann. 2018;180:249\u0026ndash;61. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.landurbplan.2018.06.001\u003c/span\u003e\u003cspan address=\"10.1016/j.landurbplan.2018.06.001\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEgharevba JO. (2025). From traditional to smart: Embedding human-centric principles into urban facility planning for inclusive development in African Cities. J Urban Dev Manage.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEgharevba JO, Onaiwu DN. Economic impact of solid waste on the livelihood of scavengers in Benin City, Nigeria. Kad J Geogr. 2020;2(2):26\u0026ndash;52.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEuropean Forest Institute (n. d.). \u003cem\u003eForestQuestions Q9: How will climate change affect forests and what can we do about it?\u003c/em\u003e Retrieved from \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://efi.int/forestquestions/q9\u003c/span\u003e\u003cspan address=\"https://efi.int/forestquestions/q9\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFederal Government of Nigeria. Climate Change Act 2021. Federal Government; 2021.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFiroozi AA, Firoozi AA, Oyejobi DO, Avudaiappan S, Saavedra Flores E. Emerging trends in sustainable building materials: Technological innovations, enhanced performance, and future directions. Results Eng. 2024;24:103521. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.rineng.2024.103521\u003c/span\u003e\u003cspan address=\"10.1016/j.rineng.2024.103521\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGetter KL, Rowe DB. The role of extensive green roofs in sustainable development. HortScience. 2006;41(5):1276\u0026ndash;85. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.21273/HORTSCI.41.5.1276\u003c/span\u003e\u003cspan address=\"10.21273/HORTSCI.41.5.1276\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGill SE, Handley JF, Ennos AR, Pauleit S. Adapting cities for climate change: The role of the green infrastructure. Built Environ. 2007;33(1):115\u0026ndash;33. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.2148/benv.33.1.115\u003c/span\u003e\u003cspan address=\"10.2148/benv.33.1.115\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHeynen N, Kaika M, Swyngedouw E. In the nature of cities: Urban political ecology and the politics of urban metabolism. Routledge; 2006.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIEA. (2021). Global status report for buildings and construction 2021. Int Energy Agency. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://globalabc.org/sites/default/files/2021-10/GABC_Buildings-GSR-2021_BOOK.pdf\u003c/span\u003e\u003cspan address=\"https://globalabc.org/sites/default/files/2021-10/GABC_Buildings-GSR-2021_BOOK.pdf\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIke C, Ezeibe C, Anijiofor-Ike CS, Daud NNN. (2018). \u003cem\u003eSolid waste management in Nigeria: Problems, prospects, and policies. The Journal of Solid Waste Technology and Management\u003c/em\u003e, 44(2), 163\u0026ndash;172. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.5276/JSWTM.2018.163\u003c/span\u003e\u003cspan address=\"10.5276/JSWTM.2018.163\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIntergovernmental Panel on Climate Change. (2022). \u003cem\u003eClimate Change 2022: Impacts, Adaptation and Vulnerability (Working Group II contribution to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change)\u003c/em\u003e. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.ipcc.ch/report/ar6/wg2/\u003c/span\u003e\u003cspan address=\"https://www.ipcc.ch/report/ar6/wg2/\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eInternational Energy Agency. (2023, March 2). \u003cem\u003eCO₂ Emissions in 2022: Growth in emissions lower than feared\u003c/em\u003e. IEA. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://iea.blob.core.windows.net/assets/3c8fa115-35c4-4474-b237-1b00424c8844/CO2Emissionsin2022.pdf\u003c/span\u003e\u003cspan address=\"https://iea.blob.core.windows.net/assets/3c8fa115-35c4-4474-b237-1b00424c8844/CO2Emissionsin2022.pdf\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJiboye AD, Adebayo JA, Obakin OA. Urban housing in Nigeria for sustainable development: Challenges and prospects. Int J Adv Eng Res Sci. 2020;7(7):478\u0026ndash;91. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.22161/ijaers.77.55\u003c/span\u003e\u003cspan address=\"10.22161/ijaers.77.55\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKamana A, Radoine H, Nyasulu C. Urban challenges and strategies in African cities: A systematic literature review. City Environ Interact. 2024;21. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.cacint.2023.100132\u003c/span\u003e\u003cspan address=\"10.1016/j.cacint.2023.100132\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e. 100132, ISSN 2590\u0026thinsp;\u0026ndash;\u0026thinsp;2520.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKochsk\u0026auml;mper E, Glass LM, Haupt W, Malekpour S, Grainger-Brown J. Resilience and the Sustainable Development Goals: a scrutiny of urban strategies in the 100 Resilient Cities initiative. J Environ Planning Manage. 2024;68(7):1691\u0026ndash;717. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1080/09640568.2023.2297648\u003c/span\u003e\u003cspan address=\"10.1080/09640568.2023.2297648\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKorhonen J, Honkasalo A, Sepp\u0026auml;l\u0026auml; J. Circular economy: The concept and its limitations. Ecol Econ. 2018;143:37\u0026ndash;46. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ecolecon.2017.06.041\u003c/span\u003e\u003cspan address=\"10.1016/j.ecolecon.2017.06.041\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu Z, Wu Q, Wang S, Wei W, Xu G. The impact of electric buses on urban air quality and CO₂ emissions. Transp Res Part D: Transp Environ. 2019;75:31\u0026ndash;45. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.trd.2019.07.006\u003c/span\u003e\u003cspan address=\"10.1016/j.trd.2019.07.006\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMuhoza JP, Zhou W. Urban Green Spaces in Africa: A Bibliometric Analysis. Environments. 2024;11(4):68. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/environments11040068\u003c/span\u003e\u003cspan address=\"10.3390/environments11040068\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNational Assembly of the Federal Republic of Nigeria. (2021). \u003cem\u003eClimate Change Act 2021\u003c/em\u003e. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://faolex.fao.org/docs/pdf/NIG208055.pdf\u003c/span\u003e\u003cspan address=\"https://faolex.fao.org/docs/pdf/NIG208055.pdf\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNowak DJ, Greenfield EJ, Hoehn RE, Lapoint E. Carbon storage and sequestration by trees in urban and community areas of the United States. Environ Pollut. 2013;178:229\u0026ndash;36. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.envpol.2013.03.019\u003c/span\u003e\u003cspan address=\"10.1016/j.envpol.2013.03.019\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOduwaye L, Ede P. Sustainable urban transport policies in Lagos: Assessing the BRT system. Cities. 2021;110:103067. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.cities.2020.103067\u003c/span\u003e\u003cspan address=\"10.1016/j.cities.2020.103067\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOECD. Effective carbon rates 2021: Pricing carbon emissions through taxes and emissions trading. Organisation for Economic Co-operation and Development; 2021.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOladokun M, Akinola O. Sustainable building materials in Nigeria: Potentials and challenges. J Constr Developing Ctries. 2020;25(1):75\u0026ndash;90. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.21315/jcdc2020.25.1.5\u003c/span\u003e\u003cspan address=\"10.21315/jcdc2020.25.1.5\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOmokaro GO. Multi-impacts of climate change and mitigation strategies in Nigeria: Agricultural production and food security. Sci One Health. 2025;4:100113. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/S2949704325000101\u003c/span\u003e\u003cspan address=\"10.1016/S2949704325000101\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOrganisation for Economic Co-operation and Development; African Development Bank; Cities Alliance; UCLG Africa. (2025). \u003cem\u003eAfrica\u0026rsquo;s Urbanisation Dynamics 2025: Planning for Urban Expansion \u0026ndash; Key messages: ECOWAS\u003c/em\u003e (West African Studies). OECD Publishing. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1787/2a47845c-en\u003c/span\u003e\u003cspan address=\"10.1787/2a47845c-en\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOrobator PO, Adahwara PO. Estimation of carbon storage and sequestration by tropical urban trees in Benin Metropolis, Edo State, Nigeria. Nigerian J Environ Sci Technol. 2022;6(1):214\u0026ndash;24. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.36263/nijest.2022.01.0347\u003c/span\u003e\u003cspan address=\"10.36263/nijest.2022.01.0347\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOstrom E. Polycentric systems for coping with collective action and global environmental change. Glob Environ Change. 2010;20(4):550\u0026ndash;7. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.gloenvcha.2010.07.004\u003c/span\u003e\u003cspan address=\"10.1016/j.gloenvcha.2010.07.004\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePage MJ, McKenzie JE, Bossuyt PM, Boutron I, Hoffmann TC, Mulrow CD, \u0026hellip; and, Moher D. The PRISMA 2020 statement: An updated guideline for reporting systematic reviews. BMJ. 2021;372:n71. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1136/bmj.n71\u003c/span\u003e\u003cspan address=\"10.1136/bmj.n71\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePaudel S, States SL. Urban green spaces and sustainability: Exploring the ecosystem services and disservices of grassy lawns versus floral meadows. Urban Forestry Urban Green. 2023;84:1618\u0026ndash;8667. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ufug.2023.127932\u003c/span\u003e\u003cspan address=\"10.1016/j.ufug.2023.127932\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePerini K, Rosasco P. Cost\u0026ndash;benefit analysis for green fa\u0026ccedil;ades and living wall systems. Build Environ. 2016;89:110\u0026ndash;21. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.buildenv.2015.09.012\u003c/span\u003e\u003cspan address=\"10.1016/j.buildenv.2015.09.012\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePirie G. (2013). \u003cem\u003eSustainable urban mobility in Anglophone Sub-Saharan Africa\u003c/em\u003e (Regional report for Global Report on Human Settlements 2013). UN-Habitat. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://unhabitat.org/sites/default/files/2013/06/GRHS.2013.Regional.Anglophone.Africa.pdf\u003c/span\u003e\u003cspan address=\"https://unhabitat.org/sites/default/files/2013/06/GRHS.2013.Regional.Anglophone.Africa.pdf\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePsistaki K, Tsantopoulos G, Paschalidou AK. An Overview of the Role of Forests in Climate Change Mitigation. Sustainability. 2024;16(14):6089. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/su16146089\u003c/span\u003e\u003cspan address=\"10.3390/su16146089\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRetta B, Coppola E, Ciniglia C, Grilli E. Constructed wetlands for the wastewater treatment: A review of Italian case studies. Appl Sci. 2023;13(10):6211. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/app13106211\u003c/span\u003e\u003cspan address=\"10.3390/app13106211\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSherman S, Fazeli H. (2022). Decarbonizing construction: The potential of cross-laminated timber. Chatham House Sustain Accelerator. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://accelerator.chathamhouse.org/article/decarbonizing-construction-the-potential-of-cross-laminated-timber\u003c/span\u003e\u003cspan address=\"https://accelerator.chathamhouse.org/article/decarbonizing-construction-the-potential-of-cross-laminated-timber\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSicard P, Pascu I, Petrea S, Leca S, De Marco A, Paoletti E, Agathokleous E, Calatayud V. Effect of tree canopy cover on air pollution-related mortality in European cities: an integrated approach. Lancet Planet Health. 2025;9(6):e527\u0026ndash;37. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/S2542-5196(25)00112-3\u003c/span\u003e\u003cspan address=\"10.1016/S2542-5196(25)00112-3\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSilva RH, Zwarteveen M, Stead D, Bacchin TK. Bringing Ecological Urbanism and Urban Political Ecology to transformative visions of water sensitivity in cities. Cities. 2024;145:104685. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.cities.2023.104685\u003c/span\u003e\u003cspan address=\"10.1016/j.cities.2023.104685\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSingh T, Arpanaei A, Elustondo D, Wang Y, Stocchero A, West TAP, Fu Q. Emerging technologies for the development of wood products towards extended carbon storage and CO₂ capture. Carbon Capture Sci Technol. 2022;4:1\u0026ndash;14. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ccst.2022.100057\u003c/span\u003e\u003cspan address=\"10.1016/j.ccst.2022.100057\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStrohbach MW, Haase D. Above-ground carbon storage by urban trees in Leipzig, Germany: Analysis of patterns in relation to urban land use. Landsc Urban Plann. 2012;104(1):95\u0026ndash;104. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.landurbplan.2011.10.001\u003c/span\u003e\u003cspan address=\"10.1016/j.landurbplan.2011.10.001\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTozluoğlu \u0026Ccedil;, Liao Y, Sprei F. Potential of e-bikes to replace passenger car trips and reduce greenhouse gas emissions. J Cycl Micromobility Res. 2024;2., Article 100043. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jcmr.2024.100043\u003c/span\u003e\u003cspan address=\"10.1016/j.jcmr.2024.100043\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTzaninis Y, Mandler T, Kaika M, Keil R. Moving urban political ecology beyond the \u0026lsquo;urbanization of nature\u0026rsquo;. Prog Hum Geogr. 2021;45(2):229\u0026ndash;52. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1177/0309132520903350\u003c/span\u003e\u003cspan address=\"10.1177/0309132520903350\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eUNEP. Global waste management outlook 2020. United Nations Environment Programme; 2020.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eUN-Habitat. World cities report 2020: The value of sustainable urbanisation. UN-Habitat; 2020.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eUwase M, Rwibasira P, Byiringiro J. Electrifying urban mobility in Kigali: Opportunities and challenges of e-motorcycles. Energy Policy. 2022;160:112653. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.enpol.2021.112653\u003c/span\u003e\u003cspan address=\"10.1016/j.enpol.2021.112653\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWorld Bank. (2023). \u003cem\u003ePopulation, total Nigeria\u003c/em\u003e. Retrieved from \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://data.worldbank.org/indicator/SP.POP.TOTL?locations=NG\u003c/span\u003e\u003cspan address=\"https://data.worldbank.org/indicator/SP.POP.TOTL?locations=NG\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"discover-cities","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Cities](https://www.springer.com/journal/44327)","snPcode":"44327","submissionUrl":"https://submission.springernature.com/new-submission/44327/3","title":"Discover Cities","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Carbon Sequestration, Urban Facility Planning, Green Infrastructure, Community Engagement, Sustainable Urban Development, Climate Mitigation","lastPublishedDoi":"10.21203/rs.3.rs-8173067/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8173067/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eCities contribute heavily to climate change but also hold solutions. This study examines how urban facilities in Benin Metropolis, Nigeria, can act as carbon sinks. A systematic review and meta-analysis, guided by PRISMA protocols, were conducted. Evidence was drawn from global, regional, and Nigerian studies on five facility types (green infrastructure, public buildings, transport, waste, and water systems). Findings show that green infrastructure and waste management are the most immediate and cost-effective strategies. They sequester carbon while tackling urgent urban problems like flooding, sanitation, and heat stress. In the medium to long term, mass timber construction, bio-based materials, electrified transport, and constructed wetlands offer transformative benefits. The study develops a framework combining Urban Political Ecology, the Circular Bioeconomy, and Sustainable Urban Development Theory. This highlights that carbon sequestration is not only technical but also political and social. Governance, justice, and local participation shape outcomes as much as technology. For Benin Metropolis, ecological opportunities exist, but governance weaknesses, outdated codes (building code, urban planning regulations, and energy and transport standard), and limited finance are major barriers. The study concludes that carbon sequestration should become a central principle of urban facility planning. Embedding it into facilities can shift Benin Metropolis from a net carbon source to a carbon sink. This approach also aligns with Nigeria\u0026rsquo;s Climate Change Act (2021) and global sustainability goals.\u003c/p\u003e","manuscriptTitle":"Carbon Sequestration as a Framework for Urban Facility Planning in Benin Metropolis, Nigeria","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-30 07:31:58","doi":"10.21203/rs.3.rs-8173067/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-01-13T05:27:28+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-01-09T21:39:24+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-01-08T19:27:20+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"245355623138315968265540972081094737510","date":"2025-12-31T10:34:01+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"18857925188541410912395406050075483724","date":"2025-12-31T09:33:14+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"249137564239503556198930225368734801798","date":"2025-12-30T19:22:54+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-12-26T08:45:00+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-12-05T08:44:36+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-12-04T13:08:21+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-12-04T11:09:18+00:00","index":"","fulltext":""},{"type":"submitted","content":"Discover Cities","date":"2025-12-04T10:58:49+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"discover-cities","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Cities](https://www.springer.com/journal/44327)","snPcode":"44327","submissionUrl":"https://submission.springernature.com/new-submission/44327/3","title":"Discover Cities","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"8539726a-e923-421a-af50-b710c44e6db3","owner":[],"postedDate":"December 30th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-21T12:25:13+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-30 07:31:58","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8173067","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8173067","identity":"rs-8173067","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}