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Sweltering summer days can put people’s health at risk. And in most parts of the U.S., hot days are increasingly common.

Kristina Dahl of the Union of Concerned Scientists analyzed how global warming will affect the frequency of days with an extremely high heat index – a combined measure of temperature and humidity.

“We found that if we fail to reduce our heat-trapping emissions, there will be a staggering expansion of the frequency and the intensity of extreme heat in most parts of the country,” she says. “Between now and mid-century, on average in the U.S., we would see the number of days with a heat index above 105 quadruple.”

That could lead to more heat-related illness and death.

Dahl says the research was eye-opening.

“It did keep me up at night and it kept my colleagues up at night,” she says. “And I think it increases our sense of urgency about how swiftly we need to be reducing emissions.”

But even with climate action, some increases in extreme heat are inevitable. So she says cities need to prepare – for example, by ensuring people have access to air conditioning or cooling centers, and planting trees.

She says planning now can help keep people safe as the climate warms.

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Reporting credit: Deborah Jian Lee/ChavoBart Digital Media.

Topics: Weather Extremes