Human-caused climate change made this month’s roasting heat in Western Europe much more likely than it would have been even just two decades ago, scientists said Friday, highlighting the rapidly escalating risks to health and livelihoods from the burning of fossil fuels.
Emissions of carbon dioxide and other heat-trapping gases have been raising temperatures worldwide for more than a century. All the extra heat at Earth’s surface allows summer weather patterns to deliver hotter days and more stifling nights than they once did.
After examining decades of temperature records, a team of scientists has concluded that a hot spell as intense as this week’s, over such a large stretch of Europe, was still rare for June in today’s climate, with a less than 1 percent chance of appearing in any given year.
But it would have been even rarer in the 2000s, when the world was roughly 1.1 degree Fahrenheit cooler than it is now. And it would have been “virtually impossible” half a century ago, when the planet was 2 degrees Fahrenheit cooler, the researchers wrote in a report.
“This event would not have been possible in June without climate change,” said the report’s lead author, Theodore Keeping, a climate scientist at Imperial College London. How frequent such heat waves become in the future depends, Dr. Keeping said, on how much nations do to cut emissions.
The report was prepared by scientists affiliated with World Weather Attribution, an initiative that analyzes extreme weather events to understand how they were influenced by human-caused global warming.
This week’s heat wave, which has shattered temperature records from Spain to Germany, is the result of a system of high pressure, parked over Europe, that has been sweeping in hot air from North Africa. Such heat domes, as they’re known, have been responsible for many summer hot spells in Western Europe.
“The weather pattern itself is not particularly unusual, but the temperatures are,” said Friederike Otto, the climate scientist who leads World Weather Attribution. “Or at least they used to be, without human-induced climate change.”
In their analysis, the researchers used temperature records to estimate how the odds of heat waves of different intensities had changed over the decades because of global warming. Their results indicate that a European heat wave comparable in likelihood to this week’s would have produced average daytime temperatures that were about 3.6 degrees Fahrenheit cooler in the 2000s and 6.3 degrees Fahrenheit cooler in 1976.
The scientists’ report has not yet been published in a peer-reviewed journal.
The researchers chose to compare this event to 1976 because Britain broiled that year in another fierce bout of summer heat.
“Many city parks caught fire, chocolates melted in shops and altar candles wilted,” according to a Reuters report from that June. On a stranded London subway train, passengers vomited and broke the windows, desperate for cool air. Some fainted.
But the 1976 heat wave wasn’t as widespread over Europe as the one this week has been, Dr. Otto said. It wasn’t as humid. And even the record highs that the mercury reached in Britain that June have been exceeded this week, according to provisional estimates from the country’s Met Office.
The weather patterns behind this week’s heat wave may not have been caused by climate change, but scientists are trying to figure out whether climate change might be making them more common or persistent over Europe. They’re also trying to better understand the complex processes in the atmosphere that churn such patterns into being.
A better understanding could someday allow forecasters to spot nascent heat waves much earlier, helping them warn the public weeks in advance, said Dim Coumou, a climate scientist at the Dutch university VU Amsterdam. “The earlier you know, the better adaptation measures you can take,” Dr. Coumou said.
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