Climate change has made the UK heatwave more likely

Climate change has made the UK heatwave more likely

Man-made climate change made last week’s deadly heatwave in England and Wales at least 10 times more likely and added a few degrees to the brutal heat, a study has found.

A team of international scientists found that the heatwave, which set a new national record at 40.3 degrees Celsius (104.5 degrees Fahrenheit), was made stronger and more likely by the accumulation of heat-trapping gases from the burning of coal, oil and natural gas . They said Thursday that temperatures in the heatwave were 2 to 4 degrees Celsius (3.6 to 7.2 degrees Fahrenheit) warmer than without climate change, depending on which method scientists used.

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

“Without climate change, we would not have seen temperatures above 40 degrees in the UK,” said the study’s lead author Friederike Otto, climate scientist at Imperial College of London, in an interview. “The fingerprint is super strong.”

World Weather Attribution, a collection of scientists around the world who conduct 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 it, examined the two-day average temperatures for July 18 and 19 across much of England and Wales and the highest temperature recorded in that period.

The highest daily temperatures were the most unusual, one event in 1,000 years in the currently warming world, but “almost impossible in a world without climate change,” according to the study. Last week’s heat broke the old national record by 1.6 degrees Celsius (2.9 degrees Fahrenheit). The average over two hot days and nights is a once-in-a-century event today, but it’s “nearly impossible” without climate change.

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

Using climate models, scientists are simulating a world without the 1.2 degrees Celsius warming since pre-industrial times and seeing how likely that heat would have been in this cooler world without the warming caused by fossil fuels. With observations, they look into history and thus calculate the probability of such a heat wave.

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

The World Weather Attribution study references another analysis that estimates that 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 has 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 encouraging people to cut greenhouse gas emissions, study co-author Gabe Vecchi said: “This heatwave, and heatwaves like this one, should remind us 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 @borenbears

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