Heat and drought extremes likely to stress ecosystem productivity equally or more in a warmer, CO2rich future

Reduced carbon uptake caused by recent heat and drought extremes raises concerns about biospheric feedbacks that amplify global warming. However, elevated carbon dioxide is expected to boost terrestrial ecosystem productivity over the 21st century, potentially alleviating some of the adverse carbon impacts of climate extremes. Using CMIP5 earth system model (ESM) results, Ian Williams and colleagues (2014 Environ. Res. Lett. 9 094011) find that the carbon impacts of heat and drought extremes in the future are likely to be similar to those seen in today\u27s climate only shifted toward fluctuations around a higher average temperature. However, they also find that extremes may become more frequent and longer lived, causing further reductions in carbon uptake. Considering that ESMs generally miss a host of heat and drought induced mortality mechanisms that could exacerbate adverse carbon impacts, it is logical to expect that the impacts of today\u27s heat and drought extremes are likely underestimates of what we can expect in the future with a high fossil emissions pathway