Heat Waves in the Age of Climate Change: Longer, More Frequent and More Dangerous


Two-thirds of the United States is expected to bake under what could be record high temperatures heading into the weekend. As a result, government agencies have issued warnings that can feel ominous.

An “oppressive and dangerous heat,” warned the National Weather Service. “Excessive heat, a ‘silent killer’,” echoed a news release by the National Oceanic and Atmospheric Administration. “Extreme heat is hazardous,” tweeted the NYC Emergency Management Department.

But people with health issues, older people and young children are especially susceptible to the effects of extreme heat. It’s a threat that grows as climate change continues.

[Scenes from around the (very hot) United States on Friday. | Scenes from New York City on Saturday.]

To understand how climate change increases the frequency of heat waves, it helps to think of the Earth’s temperature as a bell curve said Michael Mann, the director of the Penn State Earth System Science Center.

There’s another way that climate change worsens heat waves: by changing the jet stream. Those air currents in the atmosphere help move weather systems around and are driven by temperature differences, which are shrinking. So when heat waves arrive, they stay in place longer.

“We’re warming up the Arctic faster than the rest of the northern hemisphere,” said Dr. Mann. “So that’s decreasing that temperature contrast from the subtropics to the pole, and it’s that temperature contrast that drives the jet stream in the first place.”

At the same time, under certain circumstances the jet stream can get “stuck” between an atmospheric wall in the subtropics, and at the Arctic, trapping weather systems in place.

“That’s when you get these record breaking weather events,” said Dr. Mann, “either the unprecedented heat wave and drought, to wildfires and floods.”

This accounts for last summer’s European heat wave, as well as the recent European heat wave, he says, and is behind the current North American heat wave.

Nationwide, the time period in which heat waves might be expected to occur is 45 days longer than it was in the 1960s, according to the U.S. Global Change Research Program.



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