From The New York Times (Nadja Popovich and Adam Pearce):
The big increase in summer temperatures under the dark red category of extreme heat is “right in line” with what scientists expect to see as the climate warms over all, said Todd Sanford, director of research at Climate Central, a nonprofit science and news organization.
For each time period above, the distribution of summer temperatures forms what is known as a bell curve because most measurements fall near the average, forming the bump – or bell – in the middle. More extreme temperatures, which happen less frequently, fall in the wings, with heat waves on the right and cold-snaps on the left.
As the curve’s average – the top of the peak – shifts rightward over time, more temperatures in more places end up in the hot and extremely hot categories and fewer end up in the cold category.
Dr. Hansen’s curves also flatten out, which some have suggested is an indication of greater temperature variability. But other climate scientists, including Zeke Hausfather, an energy systems analyst at the University of California, Berkeley, have pointed out that this effect is mainly a reflection that some parts of the world are warming faster than others. There is no evidence that temperatures are becoming more variable in most parts of the world after warming has been accounted for.
Dr. Hansen’s data “really highlight that changes in the average, while they may seem modest, have big implications for the extremes. And that’s what’s going to affect society and ecosystems,” Dr. Sanford said. The findings reveal what has happened so far, and also provide “a glimpse to what’s in our future.”