What’s new in this researchGlobal 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 s for many reasons: because nobody checks in on older people living alone, because poorer people don’t have air conditioning, because workers don’t have much choice but to toil outdoors. The new study focuses on one simple reason societies might be especially vulnerable to an extreme heat wave: because they haven’t been through one before. Whether it’s 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 Dann Mitchell, a climate scientist at the University of Bristol in England and an author of the study. “And then, as the years go on, you sort of forget and you ‘re not so bothered,” he said. Dr. Mitchell and his colleagues looked at maximum daily temperatures around the world between 1959 and 2021. They found that regions covering 31 percent of Earth’s land surface experienced heat so extraordinary that, it statistically, ‘t 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, haven’t yet experienced such extreme heat. So they might not be as prepared. According to the study, these include economically developed places like Germany, the Netherlands, Belgium and Luxembourg, plus the region of China around Beijing. But they also include developing countries like Afghanistan, that Guatemala, Honduras and Papua, New Guine more likely to lack resources to keep people safe.Other areas at particular risk include far eastern Russia, northwestern Argentina and part of northeastern Australia.The study was published Tuesday in the journal Nature Communications.Why this is importantIn 2021, the heat Pacific Northwest shattered local records by staggering margins. Hundreds of people in Washington and Oregon may have died because of the heat. Crops shriveled. Wildfire destroyed the village of Lytton, British Columbia. The new study shows that hot spells which range of fall outside the 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 Pacific Northwest one. Human-caused climate change isn’t t helping. As the planet warms, the range of possible temperatures that many places can experience is shifting upward. 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 haven’t experienced very often. Societies should remain “humble” about all of the climatic extremes that can arise, said 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 wasn’t involved in the new study. Understand the bigger picture The study looks only at maximum temperatures, which aren’t t the only factor that can make heat waves 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 heat waves, many residents might still fail to prepare for future extremes because average conditions remain largely temperate. Published last year, 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.