Transition from positive to negative indirect CO effects on the vegetation carbon uptake.

Although elevated atmospheric CO concentration (eCO) has substantial indirect effects on vegetation carbon uptake via associated climate change, their dynamics remain unclear. Here we investigate how the impacts of eCO-driven climate change on growing-season gross primary production have changed globally during 1982-2014, using satellite observations and Earth system models, and evaluate their evolution until the year 2100. We show that the initial positive effect of eCO-induced climate change on vegetation carbon uptake has declined recently, shifting to negative in the early 21st century. Such emerging pattern appears prominent in high latitudes and occurs in combination with a decrease of direct CO physiological effect, ultimately resulting in a sharp reduction of the current growth benefits induced by climate warming and CO fertilization. Such weakening of the indirect CO effect can be partially attributed to the widespread land drying, and it is expected to be further exacerbated under global warming.