A new paper by David Lobell and his colleagues at Lawrence Livermore illustrates one of the problems with the whole “average temperature” notion ensconced in our discussions of climate change. The researchers compared outputs from 12 climate models, looking at the differences between daytime highs and overnight lows. The lows went up a little bit more than the highs but they were similar. The difference shows up in the variability. Clouds, as we know, are one area of uncertainty in climate models, and clouds play a big role in the summer daytime high. But they do not play as much of a role in overnight lows. As a result, the modelers found much greater variability in the daytime highs than in the overnight lows:
These results highlight the importance of considering separately projections for Tmax and Tmin when assessing climate change impacts, even in cases where average projected changes are similar. In addition, impacts that are most sensitive to summertime Tmin or wintertime Tmax may be more predictable than suggested by analyses using only projections of daily average temperatures.