U.S., European heat waves 'virtually impossible' without climate change, study finds

The life-threatening heat waves that have baked U.S. cities and inflamed European wildfires in recent weeks would be "virtually impossible" without the influence of human-caused climate change, a team of international researchers said Tuesday. Global warming, they said, also made China's recent record-setting heat wave 50 times more likely.

Soaring temperatures are punishing the Northern Hemisphere this summer. In the U.S., more than 2,000 high temperature records have been broken in the past 30 days, according to federal data. In Southern Europe, an observatory in Palermo, Sicily, which has kept temperature records on the Mediterranean coast since 1791, hit 117 degrees Fahrenheit on Monday, shattering its previous recorded high. And in China, a small northwest town recently recorded the hottest temperature in the country's history.

July is likely to be the hottest month on Earth since records have been kept.

"Without climate change we wouldn't see this at all or it would be so rare that it would basically be not happening," said Friederike Otto, a climate scientist at Imperial College London who helped lead the new research as part of a collaborative group called World Weather Attribution.

El Niño, a natural weather pattern, is likely contributing to some of the heat, the researchers said, "but the burning of fossil fuels is the main reason the heatwaves are so severe."

Global temperatures have increased nearly 2 degrees Fahrenheit since the start of the Industrial Revolution, when humans started burning fossil fuels such as coal and natural gas in earnest.

To determine what role that warming has played on the current heat waves, the researchers looked at weather data from the three continents and used peer-reviewed computer model simulations to compare the climate as it is today with what it was in the past. The study is a so-called rapid attribution report, which aims to explain the role of climate change in ongoing or recent extreme weather events. It has not yet been peer-reviewed.

The researchers found that greenhouse gas emissions are not only making extreme heat waves — the world's deadliest weather events — more common, but that they've made the current heat waves hotter than they would have otherwise been by multiple degrees Fahrenheit — a finding, Otto said, that wasn't surprising.

Bernadette Woods Placky, chief meteorologist at Climate Central, who wasn't involved in the research but had reviewed its findings, agreed with that assessment.

"It is not surprising that there's a climate connection with the extreme heat that we're seeing around the world right now," Placky said. "We know we're adding more greenhouse gases to our atmosphere and we continue to add more of them through the burning of fossil fuels. And the more heat that we put into our atmosphere, it will translate into bigger heat events."

Even a small rise in temperatures can lead to increased illness and death, according to the World Health Organization. Hot temperatures can cause heat exhaustion, severe dehydration and raise the risk of having a heart attack or stroke. Those risks are even higher in low-income neighborhoods and in communities of color, where research has found temperatures are often hotter than in white neighborhoods.

Heat waves in Europe last summer killed an estimated 61,000 people — most of them women — according to a recent study published in the journal Nature. A stifling heat dome in the Pacific Northwest in 2021 is believed to have killed hundreds in Washington, Oregon and British Columbia.

"Dangerous climate change is here now," said Michael Wehner, a senior scientist at Lawrence Berkeley National Laboratory who studies how climate change influences extreme weather and has published work on the 2021 heat dome. "I've been saying that for 10 years, so now my saying is 'dangerous climate change is here now and if you don't know that, you're not paying attention.'"

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