Terrestrial Carbon Sink and Clean Air Co-Benefits From China's Carbon Neutrality Policy

As the world's largest carbon emitter, China has been confronting the dual challenge of climate change and air pollution. China's quest for reducing carbon emissions will promisingly benefit the air quality, yet its impact on carbon sinks remains unclear. Here, we assess the effect of China's clean air actions and carbon neutrality policy on air quality and its associated co-benefits for terrestrial carbon sinks by integrating multiple observations and numerical modeling. We find a quadratic response of plant photosynthesis to aerosol loading due to trade-offs between diffuse fertilization effect and light limitations. The estimations show that China's air pollution suppresses terrestrial carbon uptake through aerosol-induced light limitations, leading to a 7.3% decrease in plant productivity in the 2010s. In the context of carbon neutrality pledge, the associated aerosol reductions tend to alleviate the suppression and produce an additional CO2 removal of 0.39 GtCO2 year-1. Our results uncover the enhanced terrestrial carbon sinks by aerosol mitigation, highlighting the synergy between carbon neutrality and clean air. As the world's largest carbon emitter, China has pledged to peak its carbon emissions before 2030 and achieve carbon neutrality before 2060 as an active response to climate change. China's climate strategies and efforts to reduce carbon emissions will promisingly benefit the air quality through reducing particulate matter air pollution. However, the impact of particulate pollution reductions on vegetation photosynthesis at regional and national scales remains uncertain. Here, we assess the impact of China's climate actions on climate factors and the associated ecological impacts with multiple observations and computational modeling. We find that plant photosynthesis increases under moderate particulate pollution and decreases under heavily polluted conditions. Results from models indicate that the severe air pollution at 2015 level suppresses China's ecosystem productivity, while the air quality improvements under carbon neutrality pledge significantly enhance vegetation photosynthesis and carbon absorption. Our results highlight the overlooked climate mitigation potential of reducing air pollution to enhance ecosystem productivity under China's carbon neutrality pathways. Both observation and simulation show a quadratic response of photosynthetic productivity to aerosol loading in the eastern China region Aerosol loading in China attenuates the incident shortwave radiation, which weakens plant photosynthesis and terrestrial carbon uptake Aerosol mitigation under China's carbon neutrality pursuit can enhance ecosystem productivity and promote terrestrial carbon sink