The longer heat waves stick around in one place, the longer people are exposed to life-threatening temperatures. As workers slow down during extreme heat, so does economic productivity. Heat waves also dry out soil and vegetation, harming crops and raising the risk of wildfires.

These changes to heat wave behavior have been more noticeable since the late 1990s, Dr. Zhang said. He attributes the changes in large part to human-caused climate change, but also in part to natural climate variability.

The paper is here