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Human-caused climate change made U.K. heat wave 10 times more likely, study says

Britain has experienced some relief since last week's heat wave, but the parched grass in London's of Greenwich Park is a symptom of the country's driest summer in decades. (Andy Rain/EPA-EFE/REX/Shutterstock)
4 min

LONDON — When Britain experienced its highest temperatures ever recorded, in an extreme heat wave last week, scientists had little doubt the blistering event was supercharged by humanity’s runaway release of greenhouse gases.

Now a group of researchers, using observational data and climate modeling, have sought to calculate just how much human-fueled climate change is to blame. The analysis, conducted by the widely respected World Weather Attribution group, concluded that global warming made this British heat wave “at least 10 times more likely.”

The heat smashed records, with the mercury climbing to 40.3 degrees Celsius — or 104.5 Fahrenheit — in Coningsby, England, on July 19. Temperatures at Heathrow International Airport and St. James Park in central London were just a fraction of a degree less intense.

U.K. sees hottest day on record, with temperatures hitting 40 Celsius

The researchers determined that in a preindustrial world, circa 1850, the same heat wave would have been 4 degrees Celsius cooler (according to the observational data) or 2 degrees Celsius cooler (the computer modeling suggests).

The World Weather Attribution team specializes in examining the links between ongoing weather events and climate change. It found that climate change made devastating pre-summer heat in India and Pakistan 30 times more likely; exacerbated heavy rain and killer floods in South Africa; and increased the power and damage of Japan’s Super Typhoon Hagibis.

The same group — which is composed of scientists from around the world — said the heat wave last summer in the Pacific Northwest, which saw temps in Portland spike to 116 degrees Fahrenheit, would have been “virtually impossible” before climate change.

The British heat wave would have been “extremely unlikely” without human-caused climate change, the researchers said.

Local records were beaten in 46 meteorological stations across the country. The previous record for Britain was 38.7 degrees Celsius (101.6 Fahrenheit) in 2019.

That may not sound so very hot to a person spending the summer in Karachi or Houston. But remember: the British government estimates that less than 5 percent of British homes have air conditioning. The country and its infrastructure aren’t built for these extremes.

Keep cool and carry on? Britons struggle through hottest day on record.

“Heat waves are often invisible disasters,” unlike flooding or hurricanes, said Emmanuel Raju, of the University of Copenhagen’s Centre for Disaster Research, and one of the authors of the report.

A full tally of the July heat wave’s lethality will take a month or more, as researchers pore over death certificates. But the report warns: “impacts include projections of excess mortality of over 840 people” for the two-day event, plus “hospitalizations, infrastructure damage, and psychosocial effects.”

In the world of “natural climate,” before the deployment of the steam engine in the industrial revolution, the atmospheric carbon dioxide level stood at 280 parts per million. Today it is 412 parts per million — and the planet is on average 1.2 degrees Celsius warmer.

Most of the world’s governments have pledged to keep future warming “well below” 2 degrees Celsius while pursuing efforts to limit it to 1.5.

2C or 1.5C? How global climate targets are set and what they mean

So far, the planet appears on track to blow past these targets. On current trajectories, the world is projected to warm 2.7 degrees Celsius (4.9 Fahrenheit) by the end of the century.

The analysis of the British heat wave found its likelihood in a 1.2 degrees Celsius cooler, preindustrial world was “extremely low” — and “statistically impossible” in two out of the three meteorological stations in England that they examined.

Friederike Otto, one of the study’s authors, based at Imperial College London, said because of climate change, “every heat wave is more likely and more likely to be more extreme.”

Even so, these are still rare events.

Post Reports podcast: Britain’s hottest day ever

In today’s climate, given the current levels of greenhouse gases in the atmosphere, one could expect a repeat of the British heat wave once in 100 years. For the 1-day maximum temperatures over 40 degrees Celsius, the return time is estimated at 1 in 1000 years.

But that is for the “current climate,” the researchers cautioned. Assuming greenhouse gas levels increase over the coming decades, they predict so too will the frequency of killer heat.

According to the models run by the British Meteorological Office, a 40 degrees Celsius day could happen once every 15 years by 2100 if countries meet their carbon emission promises — or once every three or four years if they continue to emit as much pollution as they do today.