The average number of heat waves in 50 major American cities has tripled since the 1960s (NYT)

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https://www.nytimes.com/2019/07/18/climate/heatwave-climate-change.html

Heat Waves in the Age of Climate Change: Longer, More Frequent and More Dangerous
By Kendra Pierre-Louis
July 18, 2019

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.

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.

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.

Climate change is shifting that bell curve toward the hotter part of the temperature scale. Even a tiny shift in the center means that more of the curve touches the extreme part of the temperature scale.

“So you know, a warming of 1 degree Celsius, which is what we’ve seen thus far, can lead to a 10-fold increase in the frequency of 100 degree days in New York City for example,” said Dr. Mann. According to the U.S. Global Change Research Program, since the 1960s the average number of heat waves — defined as two or more consecutive days where daily lows exceeded historical July and August temperatures — in 50 major American cities has tripled.

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.

As global temperatures increase, the number of deaths associated with extreme cold are predicted to decrease. At the same time, the number of deaths associated with extreme heat will increase. And those deaths, according to the National Climate Assessment, will exceed the decline in deaths from extreme cold, meaning an overall increase in mortality.

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Climate deniers, many paid by the oil industries, would say it is a coincidence, or more studies are needed.