Increased CO2 growth rate following the 2023/24 El Niño in a warming climate

Increased CO2 growth rate following the 2023/24 El Niño in a warming climate | 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 Physical Sciences - Article Increased CO 2 growth rate following the 2023/24 El Niño in a warming climate Justus Notholt, Xiaoyu Sun, Sharon Patris, Denghui Ji, Darko Dubravica, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8905743/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Atmospheric CO2 growth is correlated with the El Niño–Southern Oscillation (ENSO), showing enhanced growth associated with strong El Niño events. Here, we combine GOSAT satellite observations with new ground-based total column measurements from Palau in the Tropical Western Pacific, with surface ocean pCO2 data, to analyze the 2015/16 and 2023/24 El Niño events. We show that the CO2 response to the 2023/24 event was strong and delayed, with the largest concentration increase occurring after the El Niño peak, and it remained elevated as El Niño conditions weakened. This led to a pronounced accumulation of atmospheric CO2 over the tropical Pacific during 2024–2025. A linear regression framework explains about one-third of the historical inter-annual variability in global CO2 growth, yet it underestimates the recent increase in 2025, which cannot be explained by early oceanic forcing and exceeds expectations based on linear ENSO scaling. After oceanic forcing weakens, terrestrial carbon-cycle processes persist, as drought and heat stress in a warming climate suppress photosynthesis and enhance respiration. Such delayed amplification is characteristic of terrestrial carbon-cycle processes that integrate climate anomalies over time in a warming regime, leading to more persistent CO2 accumulation. Our results indicate that post–El Niño terrestrial amplification has shifted from a passive response to a dominant driver of sustained CO2 growth, representing a critical but previously under-observed mechanism of the global carbon cycle in a changing climate. Earth and environmental sciences/Climate sciences/Climate change/Climate-change impacts Earth and environmental sciences/Biogeochemistry/Carbon cycle Full Text Additional Declarations There is NO Competing Interest. Supplementary Files Supplementmaterialsfor.docx SUPPLEMENTARY INFORMATION Cite Share Download PDF Status: Under Review Version 1 posted 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-8905743","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Physical Sciences - Article","associatedPublications":[],"authors":[{"id":612856643,"identity":"1266334d-1ca1-4123-93af-c9b57104a367","order_by":0,"name":"Justus 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Here, we combine GOSAT satellite observations with new ground-based total column measurements from Palau in the Tropical Western Pacific, with surface ocean pCO2 data, to analyze the 2015/16 and 2023/24 El Niño events. We show that the CO2 response to the 2023/24 event was strong and delayed, with the largest concentration increase occurring after the El Niño peak, and it remained elevated as El Niño conditions weakened. This led to a pronounced accumulation of atmospheric CO2 over the tropical Pacific during 2024–2025. A linear regression framework explains about one-third of the historical inter-annual variability in global CO2 growth, yet it underestimates the recent increase in 2025, which cannot be explained by early oceanic forcing and exceeds expectations based on linear ENSO scaling.\r\nAfter oceanic forcing weakens, terrestrial carbon-cycle processes persist, as drought and heat stress in a warming climate suppress photosynthesis and enhance respiration. Such delayed amplification is characteristic of terrestrial carbon-cycle processes that integrate climate anomalies over time in a warming regime, leading to more persistent CO2 accumulation. 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