LONDON – Global warming is making dangerously hot weather more common, and more extreme, on every continent. A new study by researchers in Britain takes a unique approach to identifying which places are most at risk.

When the mercury spikes, communities can suffer for many reasons: Because nobody checks in on older people living alone, because poorer people do not have air-conditioning, because workers do not have much choice but to toil outdoors.

The new study focuses on one simple reason societies might be especially vulnerable to an extreme heatwave: Because they have not been through one before.

Whether it is heat or floods or epidemics of disease, societies are generally equipped to handle only the gravest disaster they have experienced in recent memory.

Right after a catastrophe, people and policymakers are hyper-aware of the risks and how to respond, said Dr Dann Mitchell, a climate scientist at the University of Bristol in Britain and an author of the study. “And then, as the years go on, you sort of forget and you’re not so bothered.”

Dr Mitchell and his colleagues looked at maximum daily temperatures around the world between 1959 and 2021. They found that regions covering 31 per cent of earth’s land surface experienced heat so extraordinary that, statistically, it should not have happened.

These places, the study argues, are now prepared to some degree for future severe hot spells.

But there are still many areas that, simply by chance, have not yet experienced such extreme heat. So they might not be as prepared.

According to the study, these include economically developed places like Belgium, Germany, Luxembourg and the Netherlands, plus the region of China around Beijing. But they also include developing countries like Afghanistan, Guatemala, Honduras and Papua New Guinea that are more likely to lack resources to keep people safe.

Other areas at particular risk include far eastern Russia, north-western Argentina and part of north-eastern Australia.

The study was published on Tuesday in the journal Nature Communications.

Why this is important

In 2021, a heatwave in the Pacific Northwest shattered local records by staggering margins.

Hundreds of people in Oregon and Washington may have died because of the heat. Crops shrivelled. Wildfire destroyed the village of Lytton, British Columbia.

The new study shows that hot spells which fall outside the range of statistical plausibility have occurred all over the world throughout the past few decades. This suggests they could happen again, anywhere, though not all of them will be as off-the-charts as the recent one in the Pacific Northwest.

Human-caused climate change is not helping. As the planet warms, the range of possible temperatures that many places can experience is shifting upwards.

Scorching heat that would once have counted as unusual is becoming more likely.

But the weather has always varied a great deal, and the most exceptional events are ones that, by definition, people have not experienced very often.

Societies should remain “humble” about all the climatic extremes that can arise, said Dr Karen A. McKinnon, an assistant professor of statistics and the environment at the University of California, Los Angeles.

“We’re often not even prepared for that baseline level of variability,” said Dr McKinnon, who was not involved in the new study.

Understand the bigger picture

The study looks only at maximum temperatures, which are not the only factor that can make heatwaves devastating.

Humidity is also important, as are sweltering overnight temperatures, which eliminate opportunities for people to cool down from oppressive daytime conditions.

In general, relief from heat – in the form, for instance, of green or air-conditioned spaces – is less accessible to the poor than to the rich.

Even in places that have already experienced record-shattering heatwaves, many residents might still fail to prepare for future extremes because average conditions remain largely temperate.

In research published in 2022, Dr McKinnon showed that, in the Pacific Northwest, very high summertime temperatures occurred more often than one would expect, given the region’s generally mild climate. NYTIMES