Trends in carbon sink along the Belt and Road in the future under high emission scenario

Over the past three decades, the drawdown of atmospheric CO2 in vegetation and soil has fueled net ecosystem production (NEP). Here, a global land-surface model (CABLE) is used to estimate the trend in NEP and its response to atmospheric CO2, climate change, biological nitrogen (N) fixation, and N deposition under future conditions from 2031 tO(2)100 in the Belt and Road region. The trend of NEP simulated by CABLE decreases from 0.015 Pg carbon (C) yr(-2) under present conditions (1936-2005) to - 0.023 Pg C yr(-2) under future conditions. In contrast, the trend in NEP of the CMIP6 ensemble changes from 0.014 Pg C yr(-2) under present conditions to - 0.009 Pg C yr(-2) under future conditions. This suggests that the trend in the C sink for the Belt and Road region will likely decline in the future. The significant difference in the NEP trend between present and future conditions is mainly caused by the difference in the impact of climate change on NEP. Considering the responses of soil respiration (RH) or net primary production (NPP) to surface air temperature, the trend in surface air temperature changes from 0.01 degrees C yr(-1) under present conditions to 0.05 degrees C yr(-1) under future conditions. CABLE simulates a greater response of RH to surface temperature than that of NPP under future conditions, which causes a decreasing trend in NEP. In addition, the greater decreasing trend in NEP under future conditions indicates that the C-climate-N interaction at the regional scale should be considered. It is important to estimate the direction and magnitude of C sinks under the C neutrality target.