text: Increasing the air temperature by 2C increased ecosystem evapotranspiration ; but the imposition of twice-ambient atmospheric CO 2 concentrations reduced this impact of the temperature increase while simultaneously enhancing ecosystem net primary production. Thus, ecosystem water-use efficiency rose under conditions of simultaneously-elevated air temperature and CO 2 concentration. In addition, the air temperature increase had little effect on soil organic carbon content, boosting it by only 1%. Doubling the atmospheric CO 2 concentration, on the other hand, increased soil carbon storage by 5%; and when both air temperature and CO 2 concentration were increased together, the simulated increase in soil carbon content was a full 10%. What it means