While heat waves are shaped by complex local factors such as urbanization and land use, scientists no longer have much doubt about whether climate change is making them worse. Soon, the world’s most devastating heat waves may simply have no historical analogue from the time shortly before humans starting pumping greenhouse gases into the atmosphere, some scientists argue, rendering obsolete the question of whether climate change is a main driver. If the threshold for a heat wave is just the mercury exceeding 100 degrees Fahrenheit for days in a row, for instance, then it’s “not at all unexpected,” Dr. Dessler said, to see them occurring more regularly in several regions at once. Yet even when scientists look at how often temperatures exceed a certain level relative to a moving average, they still find a big increase in the frequency of simultaneous heat waves. But the number of days with two or more heat waves was seven times higher, growing to roughly 143 from 20.

Source: International New York Times June 25, 2022 12:08 UTC