Climate change made Britain’s heatwave hotter, more likely

Man-made climate change made last week’s deadly heat wave in England and Wales at least 10 times more likely and added a few degrees to how brutally hot it got, a study said.

A team of international researchers found that the heat wave that set a new national record high of 40.3 degrees Celsius (104.5 degrees Fahrenheit) was made stronger and more likely by the build-up of heat-trapping gases from the burning of coal, oil and natural gas. They said Thursday that temperatures were 2 to 4 degrees Celsius warmer (3.6 to 7.2 degrees Fahrenheit) during the heat wave than they would have been without climate change, depending on which method the researchers used.

The study has not yet been published in a peer-reviewed scientific journal, but follows scientifically accepted techniques, and previous such studies have been published months later.

“We would not have seen temperatures above 40 degrees in Britain without climate change,” senior author Friederike Otto, a climate scientist at Imperial College London, said in an interview. “The fingerprint is super strong.”

The World Weather Attribution, a collection of scientists around the globe who do real-time studies of extreme weather to see if climate change played a role in an extreme weather event and if so how much of one, looked at two-day average temperatures for July 18 and 19 in large parts of England and Wales and the highest temperature reached at that time.

The highest daily temperatures were the most unusual, a once-in-1,000-year event in the current warmer world, but “almost impossible in a world without climate change,” the study said. Last week’s heat broke the old national record by 1.6 degrees Celsius (2.9 degrees Fahrenheit). The average of two warm days and nights is a once-in-a-century event now, but is “almost impossible” without climate change.

When the researchers used the long history of temperatures in England to determine the impact of global warming, they saw a stronger climate change than when they used simulations from climate models. For some reason that scientists aren’t entirely sure about, climate models have long underestimated extreme weather signals in summer in Western Europe, Otto said.

Using climate models, researchers simulate a world without 1.2 degrees Celsius (2.2 degrees Fahrenheit) of warming since pre-industrial times and see how likely this warming would be in the cooler world without fossil fuel heating. With observations, they look at history and calculate the chances of such a heat wave that way.

“The methodology seems reasonable, but frankly, I didn’t need a study to tell me this was climate change,” said University of Georgia meteorology professor Marshall Shepherd, who was not part of this study team but was on a US National Academy of Sciences panel that said that these types of studies are scientifically valid. “This new era of heat is particularly dangerous because most homes are not equipped for it.”

The World Weather Attribution study cites another analysis that estimates a heatwave like this would kill at least 800 people in England and Wales, where there is less air conditioning than in warmer climates.

Otto, who had to sleep and work in the basement because of the heat, said as the world warms, these record-breaking heat waves will continue to come more frequently and hotter.

In addition to spurring people to cut greenhouse gas emissions, study co-author Gabe Vecchi said, “this heat wave and heat waves like it should be a reminder that we need to adapt to a warmer world. We don’t live in our parents’ world anymore.”

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Follow Seth Borenstein on Twitter at @borenbjørner

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