Earth system model-based assessment of carbon removal potential and climate effects of afforestation

In the context of global climate change, the ecological and climatic effects of afforestation as a key carbon removal technology are regulated by soil moisture. In this study, based on UVic_ESCM, we modelled the long-term effects of afforestation on carbon cycling and climate in the mid-latitude region of the Northern Hemisphere under the SSP5-8.5 scenario with different soil moisture (A1:330 kg/m2, A2:360 kg/m2, A3:390 kg/m2). The results showed that A3 significantly enhanced CO2 uptake capacity, reducing atmospheric carbon by 203.8 Gt C and increasing terrestrial carbon by 267.9 Gt C in 2099, which was four times more efficient than that of A1, but the long-term carbon sink rate slowed down due to saturation effect.A3 achieved a cumulative reduction of 0.32°C in surface temperature by enhancing transpiration and optimizing the energy balance, while A1 counteracted to cause a slight warming (+0.21°C). Regional analysis showed significant carbon gain in tropical plants and dominance of carbon accumulation in temperate soils. This study reveals that soil moisture is a key variable in optimizing the climate benefits of afforestation projects, providing a quantitative basis for regional strategy development and emphasizing the need to balance carbon sink gains with water sustainability.