Increasing global land surface soil organic carbon under climate change

Abstract Soil organic carbon (SOC), especially land surface SOC is sensitive to climate change as a sink or source of atmospheric carbon dioxide, which is an important component of the global carbon cycle and could play a key role in global carbon neutrality. However, it is still an open question about how global surface SOC change with climate warming. Here we show global SOC has a significant upward trend during 1981-2019. Temperature and precipitation are the dominant climate drivers at global scale, but vegetation cover is a crucial local factor. By integrating with climate scenarios of CMIP6 models, we project the future increase in global surface SOC with warming temperature, especially in middle and low latitudes. SOC change shows a lag feedback and limited balance role depending on the regional vegetation changes. Under 1.5oC global warming level, land carbon sink from SOC will maximally increase by 13.0 PgC from SSP2-4.5, but it only accounts for 19% of carbon emission capacity from current 1.1 to 1.5 oC global warming level. It is far from the Paris Agreement plan of four out of one thousand soil carbon stock of 40cm below the surface increase per year in the next 20 years (2.72 PgC yr-1). Moreover, this contribution is full of uncertainties and confined to support large-scale carbon dioxide removal from the atmosphere. Over-reliance on natural carbon sinks is a risky strategy. These findings highlight the urgency to carry out mitigation and removal strategies of reducing greenhouse gas emissions for the global carbon equilibrium and the Paris Agreement target.