Global warming accelerates plant water use, increasing plant susceptibility to drought death. From this, it can be hypothesised that higher CO2 concentrations slow plant water use, and should offset the warming effects on mortality.
Using six years of data from a field experiment, Hovenden et al. demonstrate that the timing of rainfall has a major influence on the impacts of warming and elevated CO2 on plant mortality. Elevated CO2 moderated the increase in mortality caused by warming, but only in years with few dry spells. The timing of wet spells is shown to be a crucial determinant of how climate change influences plant mortality.
Hovenden, M. J., Newton, P. C. D., & Porter, M. (2017). Elevated CO2 and warming effects on grassland plant mortality are determined by the timing of rainfall. Annals of Botany, 119(7), 1225–1233. https://doi.org/10.1093/aob/mcx006