The increase is consistent with what climate scientists have warned for decades: A seemingly small change in global average temperature (so far, about 1.2 degrees Celsius of warming since pre-industrial times) can lead to big changes in extreme heat.

Hotter summers also make the effects of global warming harder for the public to ignore, Dr. Hansen said via email. “People notice the extremes,” he wrote.

Dr. Hansen’s temperature curves also flatten out over time, as they move rightward, toward higher heat. Zeke Hausfather, a climate scientist at Berkeley Earth, said this largely reflects that some parts of the world are warming faster than others.

Overall, Dr. Hausfather said, the data provides “a good visualization of how when we focus just on the global average, we’re missing a lot of what’s happening.”