As heat waves become more frequent and droughts cause famines and drive up food prices, climate policies will need to account for changes in extremes in temperature and precipitation, as global mean temperatures continue to rise through the 21st century. Using HadGEM2, a new ocean-atmosphere coupled climate model, Caesar and Lowe investigated the effects of different greenhouse gas emissions scenarios on maximum and minimum air temperatures as well as on the amounts of rainfall in different parts of the world. The authors compared two scenarios through the 21st century, the first one with an aggressive mitigation scenario, in which global emissions begin to decrease in the early 21st century and reach nearly zero by 2100; the second scenario had no mitigation. The researchers' results show that extreme temperatures would scale with increasing mean temperature, at least until the middle of the 21st century: As air temperatures increase, countries across the globe would experience hotter days and an increasing number of heat waves, even with aggressive mitigation. However, mitigation may provide some amelioration, particularly through the second half of the 21st century; the northern midlatitudes would benefit most from mitigation measures, although northern South America and parts of the United States, Africa, and Asia could also avoid large increases in extreme temperature maxima by following similar mitigation policies.