Every heatwave occurring today is more intense due to climate change

It’s no longer important to use modelling to determine whether a heatwave was made more likely by climate change, say scientists, because all heatwaves today are climate change-related

By Adam Vaughan

Every heatwave today was made more likely by climate change and there is no longer a need to wait for studies to tease out global warming’s role in individual extreme heat episodes, according to the scientist who pioneered such studies.

Researchers usually caution against blaming specific extreme weather events on climate change. Heatwaves in China and Japan this week would not usually have been considered caused by climate change before “attribution studies” are run to model the difference in likelihood of the heatwaves between a world with our changed climate and one without. Such studies have come of age in the last decade, led by Friederike Otto of Imperial College London, and can now be turned around in days.

However, Otto says for heatwaves at least, we no longer need to wait before declaring climate change’s role. “I think we can very confidently now say that every heatwave that is occurring today has been made more intense, and more likely because of climate change,” she says. While changes to land use might after affect the likelihood, she adds: “There is no doubt that climate change is really an absolute game-changer when it comes to heatwaves.”

Nonetheless, she says studies will still be needed to know exactly how much more likely and intense heatwaves were made by climate change. “I think we shouldn’t stop doing attribution,” says Otto.

But the status quo, in which many of those studies are carried out by volunteer efforts, such as the World Weather Attribution project that Otto is a part of, is “definitely not sustainable”, she adds. National weather agencies, such as the UK’s Met Office, should conduct more of the studies to build up a picture of climate change impacts, say Otto and her colleagues in a review of attribution science published today.

Peter Stott, head of climate attribution at the Met Office, says such work is already being performed at the organisation. “We’ve been conducting climate attribution research at the Met Office for over two decades and we’re now able to rapidly attribute some extreme events using a peer-reviewed method,” he says.

Luke Harrington at Victoria University of Wellington, New Zealand – one of Otto’s colleagues – says heatwaves are the extreme weather type that is changing fastest due to climate change. “You’ll see a greater increase in the frequency of severe heatwaves with every additional degree of global warming, compared with the changing the frequency of other types of extreme weather.”

Most severe droughts around the world, by comparison, are not attributable to climate change, the review found. And neither are most wildfires, with a high confidence in a climate link only found in increasingly frequent fires in the western US. However, heavy rainfall events have been found to have increased in most part of the world due to climate change, and nowhere on Earth has the likelhilhood strongly decreased.

Heatwaves linked to climate change were found to have killed 157,000 people worldwide between 2000 and 2020, with four-fifths of those deaths occurring during the 2003 European heatwave and 2010 Russia heatwave. Harrington says the toll is almost certainly an underestimate due to many parts of the world having no monitoring of heatwaves and often no definition of one. Of the total, only 6.3 per cent of deaths were recorded in Asia, Africa, South and Central America and the Caribbean, despite almost 85 per cent of the world’s population living in these regions.

Journal reference: Environmental Research: Climate, DOI: 10.1088/2752-5295/ac6e7d

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