Effects of CO₂ vegetation forcing on precipitation and heat extremes in China

Anthropogenic CO2 emissions are expected to significantly impact climate patterns, including extreme heat events. The influence of plants on land-atmosphere water and energy exchanges plays a crucial role in shaping these heat extremes. The response of vegetation growth and physiology to elevated CO2, both directly and indirectly, will determine their contribution to future heat extremes. In this study, we employed a suite of CMIP6 earth system models (ESMs) to differentiate between the effects of radiative forcing and vegetation forcing under elevated CO2 background on extreme heat and precipitation events in China. The CO2 vegetation forcing may reduce transpiration and weak vegetation cooling impact, leading to a decrease in clouds and precipitation under 2 x CO2 and 4 x CO2 scenarios. Our findings indicate that CO2-driven vegetation forcing (VEG) decreases extreme precipitation and increases dry days numbers in most humid regions of China, despite the increase in transpiration resulting from the saving of soil moisture and aboveground biomass enhancement due to CO2 fertilization. Additionally, VEG intensifies the frequency and intensity of future heatwaves over most of China. Both radiative forcing and vegetation forcing have a stronger impact on humid area than dry area. The findings indicate that solely considering the radiative impacts of CO2 is insufficient to explain the projected variations in extreme precipitation and heat changes. It suggests that CO2 physiological forcing might play a role in influencing the differences in projected water and energy characteristics among different climate models.