Climate change made deadly UK heat wave at least 10 times more likely: study


The heat wave in the UK earlier this month caused so many fires in London that the city’s fire brigade was busier than at any time since the Nazi attacks in World War II. More than 840 people may have died in England and Wales, according to a preliminary analysis. Now a quick scientific analysis of the event concludes that these conditions would have been “extremely unlikely” without climate change.

World Weather Attribution, the research team who conducted the study, looked at the weather in the southern half of the country on July 18-19 and analyzed both peak temperatures and two-day averages. The analysis, released Thursday, found that greenhouse gas pollution made the heat wave at least 10 times more likely and made it 4° Celsius (7.2° Fahrenheit) hotter than it would have been.

Coningsby, Lincolnshire, in the east of England, set a new heat record in the UK of 40.3°C (104.5°F) on July 19, breaking the previous record set in 2019 by 1.6°C. Forty-six weather stations in the UK recorded new highs. The heat wave also set another milestone for what scientists refer to as confusingly high minimums, or actually hot nighttime temperatures. The country’s new overnight heat record is 25.8°C, nearly 2°C hotter than the 1990 level.

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The scientists at World Weather Attribution used two methods: a statistical approach to the temperature record and an analysis that combines historical data with multiple climate models. The team’s methodology is peer-reviewed. With a verified approach, team members can perform a quick analysis, which itself is not immediately peer-reviewed.

Low water levels reveal the bottom of Woodhead Reservoir in Longdendale, UK, on ​​July 19. Photo credit: Anthony Devlin/Bloomberg

Heat waves are the most straightforward type of extreme weather for scientists to study because they can view temperature records without the added complexity of atmospheric and water system dynamics that give rise to cyclones, droughts and wildfires. The effect of greenhouse gas pollution on temperature in general is so pronounced that WWA says it no longer needs to study every heat wave to know the influence is there.

“[G]As a direct result of climate change, the previously very rare heat is now simply unusual,” they write. “While in some cases, events now considered ‘extreme’ are reaching temperatures that were previously virtually impossible.”

WWA has become an authority for making connections between global warming and extreme weather such as droughts and storms. Much of his work focuses on intense heat. The June 2021 heatwave across the western US-Canada border would have been “virtually impossible” without climate change. Heat this spring in India and Pakistan was 30 times more likely due to greenhouse gas pollution. Siberian heat in the first half of 2020 was 600 times more likely.

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Each heat wave arises against a local background of forces. But sometimes variability in WWA’s results can arise from the limitations of available tools. These may explain why their conclusions about seemingly similar heat waves may differ. For example, models sometimes underestimate the magnitude of human-induced warming to date. That means that analyzes that combine observations and models “are almost certainly too conservative,” the group wrote in a summary of its findings.

“It would have been four degrees cooler without climate change, but in the models we only see it is two degrees cooler without climate change,” said Friederike Otto, senior lecturer in climate science at Imperial College London and leader of WWA. “Which means we can’t — with the tools we have available today — we can’t really quantify the role of climate change in a very satisfying way.”

To guide the primary analysis, the team looked at temperature histories for three specific weather stations. For St. James Park, Cranwell, near where the new British record was set, the heat was a 1 in 500 year event. For Durham, which has temperature records dating back to 1880 and broke its local record by 4°C, the heat wave had a once in 1500 year chance. Those calculations were made based on the current climate – already 1.2 °C hotter than before industrialization.

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The UK is ahead of most of the world when it comes to preparing for extreme heat. The heat wave plan for England, first issued a year after the 2003 European heat wave, which spurred the formal study of climate impacts on extreme weather, was revised in 2012 and deployed this month to communicate health risks broadly and clearly. . The government has issued its first color-coded heat warning, “amber,” which warns of temperatures so high that “fit and healthy” people, not just those at high risk, could be susceptible to illness or even death.

–With help from Kevin Simauchi.

Photo: A firefighter carries a bucket of water to fill the ground, following a major fire during a heatwave, on Dartford Heath near Dartford, UK, on ​​Wednesday 20th July 2022. Fires broke out across London and the city’s fire brigade declared a major incident, in the latest sign of how record-breaking heat was wreaking havoc in the UK. Photo credit: Chris Ratcliffe/Bloomberg

Copyright 2022 Bloomberg.

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