The heat that shattered records in Britain last week, bringing temperatures as high as 104.5 degrees Fahrenheit to a country unaccustomed to scorching summers, would have been “extremely unlikely” without the impact of human-caused climate change, according to one new scientific report published on Thursday found.
Heat at the intensity of the past week is still highly unusual for Britain, even with the current level of global warming, said Mariam Zachariah, a research fellow at Imperial College London and lead author of the new report. The odds of seeing the daily highs that some parts of the country recorded last week were about 1 in 1,000 any year, she and her colleagues found.
Still, said Dr. Zachariah, these temperatures are at least 10 times more likely than in a world with no greenhouse gas emissions and at least 3.6 degrees Fahrenheit hotter.
“This is still a rare event today,” said Friederike Otto, a climate scientist at Imperial College London and also an author of the report. “Without climate change, it would have been an extremely unlikely event.”
Severe heat has become more frequent and intense in most regions of the world, and scientists have little doubt that global warming is a major factor. As the burning of fossil fuels causes average global temperatures to rise, the range of possible temperatures is also shifting upwards, making blistering heights more likely. This means that every heatwave is now, to some extent, exacerbated by changes in planetary chemistry caused by greenhouse gas emissions.
Before last week, the highest temperature Britain had ever recorded was 101.7 Fahrenheit, or 38.7 degrees Celsius, a milestone set in Cambridge in July 2019. This month, as temperatures soared, the country’s weather regulator, the Met Office, warned Brits to brace for new highs.
Mercury topped the old record on the morning of July 19 in the village of Charlwood, Surrey, and continued to rise. By the end of the day, 46 weather stations, stretching across most of England from London in the south-east to North Yorkshire in the north-east, had recorded temperatures that equaled or exceeded the previous national record. Other broadcasters beat their own local records by 5 to 7 degrees Fahrenheit.
In response, trains were slowed for fear that the steel rails would buckle in the heat. Grass fires spread to London’s homes, shops and vehicles in what the city described as the busiest day for firefighters since World War II. According to this, more than 840 more people may have died in England and Wales than would have been usual preliminary examination using peer review methodology.
The report on last week’s heat was produced by World Weather Attribution, an alliance of climate scientists specializing in rapid studies of extreme weather events to assess the extent to which global warming is behind them. Using computer simulations, the scientists are comparing the existing world, where humans have spent more than a century adding heat-trapping gases to the atmosphere, to a world where this activity may not have existed.
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The group’s analysis of the UK heat has not yet been peer-reviewed or published in a scientific journal, but it uses peer-reviewed methodologies.
Using similar techniques, the group found that the heatwave that hit South Asia this spring was 30 times more likely to occur due to emissions warming the planet.
Much of western and central Europe had a very hot start to the summer, fueled by a high pressure area that brought in warm air from North Africa. England experiences the driest July in more than a century. When the ground has dried out, the sun’s energy is used to heat the air instead of evaporating water on the ground, which can contribute to even hotter temperatures.
Scientists reported this month that heat waves in Europe have increased in frequency and intensity over the past four decades, due at least in part to changes in the jet stream.
For some scientists, the recent heat in Britain was reminiscent of last summer’s deadly temperatures in the Pacific Northwest, which broke records of 7 degrees Fahrenheit or more in some places. This heat was so extraordinary that some climate scientists wondered if extreme heat was occurring faster than their scientific models allowed for. Erich Fischer of the Swiss university ETH Zurich said it was the climate equivalent of an athlete beating the long jump record by 2 or 3 feet.
So far, however, the evidence suggests that such events are surprising but not unpredictable with current models. dr Fischer led a study last year that showed that global warming, with its seemingly small increase in average temperatures, also increases the likelihood of wide-ranging heat records being broken.
The question, as with floods, droughts and other extremes, is whether policymakers will use this knowledge to better prepare in advance.
“There are conditions that usually turn these hazards into disasters, and these conditions are man-made,” said Emmanuel Raju, associate professor of public health at the University of Copenhagen and another author of the UK heat report. Those conditions include poor planning and a lack of attention to vulnerable groups like the homeless, said Dr. raju
Vikki Thompson, a climate scientist at the University of Bristol, led another recent study that found that while hot extremes have become more common around the world in recent decades, most could still be explained by higher average temperatures due to climate change. “They’re increasing in intensity, just not faster than average,” said Dr. Thompson.
But even this pace of increase is testing countries’ ability to cope. The British rail system was designed to only run safely up to 80.6 degrees Fahrenheit. Most homes are designed to retain heat during freezing winters. Many Brits still see hot weather as a welcome respite from the cold and damp.
In the UK, “people are still not taking it quite as seriously as maybe next time,” said Dr. Thompson. “A heatwave is viewed by most people as something big to come. They want some warmth.”
“But when it’s 40 degrees,” or 104 Fahrenheit, she said, “that starts to change.”