Climate effects of ecosystem change converge according to the ratio of the daytime to daily vapor flux.

Ecosystem changes can simultaneously generate various climate-related effects, such as evapotranspiration (vapor flux) effects, carbon-cycle effects, and surface temperature effects. These effects are coupled with one another because they are generated through the same biophysical and biogeochemical processes. Consequently, given an easily measurable effect, other effects can be predicted from the measured effect. Here, based on global eddy covariance (EC) observations, we show that the ratio of the daytime to daily vapor flux (RATIO) reflects the complexity of various ecosystem types and is highly coupled with climate effects of ecosystem changes. For the same daily RATIO, the magnitudes of the same EC variable remain unchanged across all of the ecosystems and, thus, EC observations for an ecosystem or place can be mapped to other ecosystems or places in accordance with their daily RATIO values. By applying the daily RATIO, the effects of ecosystem changes on the surface temperature in different climatic zones (including the Tibetan Plateau) can be predicted, which is highly consistent with all previous studies. We found that cooling or warming effects are controlled by the RATIO, not by enhanced or reduced evapotranspiration as many studies have suggested. This study provides a new and simple approach for evaluating the climate effects of ecosystem changes at all spatial-temporal scales worldwide.