Vegetation Physiological Response to Increasing Atmospheric CO2 Slows the Decreases in the Seasonal Amplitude of Temperature

The seasonal amplitude of temperature (SAT) decreases due to non-uniform seasonal warming, which exerts critical impacts on ecosystem functions and services. Previous studies attributed the SAT decrease to changed seasonal budget of atmospheric radiative forcing (RAD), however, potential impacts of vegetation physiological response to CO2 (PHY) on SAT are largely underexplored. Here, we examine the role of PHY in modulating SAT using Earth system model simulations. Globally, PHY continuously increases SAT, offsetting about 55% of the RAD-driven SAT reductions under quadrupled CO2. The PHY-induced SAT enhancement is particularly pronounced in the northern mid-to-high latitudes. Such enhancement is driven directly by stomatal closure-induced evapotranspiration reduction that amplifies warming, and indirectly by suppressing cloud formation that increases downward shortwave radiation. Our results highlight the critical role of vegetation in mediating temperature seasonality and the necessity for a full understanding of PHY feedback when evaluating the benefits of terrestrial ecosystems in mitigating climate change.