Climate change may make summer nights a lot sweatier, and potentially even deadly. The number of extremely hot days followed by intensely hot nights could jump to 32 days – four times as many as there are currently – in northern hemisphere summers by 2100, even if the world acts to check global warming.

In the worst-case warming scenario, which is seen as unlikely, the number leaps to 69 days, or three-quarters of summer days.

Typically, scientists have looked at how climate …