Recent intensification of the negative physiological effect of CO2 on terrestrial evaporation

The net physiological effect of rising atmospheric carbon dioxide (aCO2) on terrestrial evaporation (ET) is highly uncertain. While increased CO2 fertilization elevates ET through more biomass production, the reduction in stomatal conductance (gs) that it downregulates ET. Here, using satellite-based estimates of ET and dynamic vegetation models, we investigate the physiological influence of aCO2 on ET, and isolate the respective contribution of biomass increase and gs reduction. Our results indicate that the CO2 fertilization had a net negative effect of –4.4±0.3×10–2 mm ppm–1 on ET over 1982–2018. The negative physiological effect tends to intensify with increasing aCO2, particularly in warm and humid forests. The high sensitivity of ET to gs may attenuate the expected water cycle acceleration over land, although the future evolution of these two competing physiological processes remains uncertain.