198 had an increase in the average number of days each year that felt 90F or hotter and 106 cities had an increase in ‘danger’ days that felt 105F or hotter

This article is more than 1 year old

This article is more than 1 year old

Nearly 200 US cities have seen an increase in the number of days each year that soar beyond a heat index of 90F (32.2C) or higher, according to an analysis of the last four decades.

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“These extreme heat days are now comprising much of the summer for many cities in the south and south-west, while areas of the country that had relatively few summer days reach the 90F heat index in the past are now experiencing weeks of them,” said the report from the climate communications organization Climate Central.

The higher temperatures are threatening public health and making outdoor activities and sports more dangerous. A July heatwave in the midwest and eastern US forced the cancellation of the New York City Triathlon, as well as other running and horse races.

Climate Central used heat heat and humidity data for 239 cities and found 198 had an increase in the average number of days each year that felt 90F or hotter. They also found that 106 cities had an increase in “danger” days that felt 105F or hotter.

Globally, temperatures are 1.5F higher than they were in the middle of the last century, as humans’ power plants, cars and ways of living contribute pollution that heats the planet.

Q&A Why is heat an issue in US cities? Show Hide Donald Trump is pulling the US out of the Paris climate accord - meanwhile sweltering US cities are facing ever greater challenges on coping with heat and the climate crisis. This year saw the hottest July on record and many US cities have endured heatwaves - including those as far north as Alaska, where thermometers hit 90F (32C) for the first time. This week Guardian Cities is examining the growing challenges for US cities and the best ideas for reducing the impact of the climate crisis on communities. Mark Oliver, special projects editor, Guardian US

In parts of the Pacific north-west, days that were 90F or hotter increased substantially. In Yakima, Washington, they more than doubled, from 13 to 29.

Salt Lake City, Utah, is seeing two weeks of days that hot. Fresno, California, saw a jump from 78 days to 93.

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In the south, extreme heat isn’t just in the summer. Austin, Texas, had 126 days that felt like 90F or hotter on average for the last five years. Savannah, Georgia, had 114. And Miami had 161.

Danger days, which feel 105F or hotter, are rare but deadly. The National Weather Service can issue an “excessive heat warning” when two days in a row are forecast to be that hot without a cool night in between.

With those temperatures, NWS warns people who don’t take precautions can become seriously ill or die.

People in McAllen, Texas, have seen the biggest increase in danger days, climbing from 16 each year to 38.

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