Projection of the Status and Future Shifts of Topsoil Organic Carbon Stocks in Northern Hemisphere Permafrost Regions: Patterns and Drivers

Abstract

The Northern Hemisphere (NH) permafrost areas harbor vast reservoirs of soil organic carbon (SOC), which are potentially at serious releasing risk due to climate change. However, projections of future changes in SOC stocks in these regions remain subject to large uncertainties. In this study, we constructed an integrated approach that combines space‐for‐time substitution with a machine learning model to estimate the current status of surface (0–30 cm) SOC stocks in NH permafrost regions and to project their future changes throughout the 21st century under various Shared Socioeconomic Pathways (SSPs). The results indicate that approximately 224.2 Pg C were stored in NH permafrost regions during the baseline period (1981–2000), and they will remain relatively stable (−0.5% ± 0.9%) until the conclusion of 21st century under SSP1‐2.6, while a significant loss of about 8.5% ± 3.5% is projected under SSP5‐8.5. Spatially, the areas with increased surface SOC in the future are mainly located in the continuous permafrost zone, while the decrease is identified in most of discontinuous, sporadic, and isolated permafrost areas. Among ecosystems, grasslands and deserts are projected to act as future carbon sinks, while forests exhibit the largest declines. Temperature exerts the strongest control on SOC dynamics in the northern circumpolar (NC) permafrost region through a nonlinear threshold effect, whereas precipitation and vegetation productivity govern SOC changes in the Third Pole. These results highlight pronounced spatial heterogeneity of SOC dynamics in permafrost regions, providing valuable insights for carbon–climate feedback assessments and regional policy.