Extreme heat is a global killer — and worse for our health than previously thought, new research shows

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More than 1,000 people died as temperatures hit nearly 52 C during this year's hajj in Saudi Arabia. Around 2,300 cases of heatstroke and dehydration were reported during Mexico's recent stretch of extreme heat. Eight known deaths occured in just 72 hours amid India's longest heatwave on record. 

We're only halfway through 2024, yet the global death toll from surging temperatures has been staggering, and a clearer picture is now emerging of extreme heat as one of the deadly emergencies facing regions around the world.

It's no secret, of course, that high heat can kill you. Doctors have long warned that rising temperatures lead to conditions like heatstroke — a life-threatening medical emergency where your body simply can't stop overheating — or exacerbate underlying illnesses like diabetes, asthma, or cardiovascular disease.

What's new is just how many people are dying as global temperatures continue to rise, including across Canada and the northern U.S., where high heat previously wasn't a top-of-mind concern.

More than 100 Canadian heat records were smashed on Wednesday alone, all while emerging research reveals the toll of high heat on the human body is far worse than previously thought.

"Most [Canadians] would probably take a look at these headlines and think, oh, it doesn't really concern me," said Toby Mündel, a Canada Research Chair in Extreme Human Environments and a professor of kinesiology at Brock University in St. Catharines, Ont.

"Not only is it going to happen to you, but it's something that you can probably prepare for," Mündel said.

A report last month by leading climate scientists examined 76 extreme heat waves across 90 countries over a 12-month period starting in May 2023.

In that period, 6.3 billion people — roughly 78 per cent of the population — experienced at least 31 days of extreme heat that were "made at least two times more likely due to human-caused climate change," the report said.

Andrew Pershing, vice-president of climate science at the U.S.-based Climate Central, one of the organizations behind the study, has been tracking the heat wave that blanketed a large part of the U.S. and eastern Canada over the past week.

"This whole region is experiencing at least one day that's at Level 2 or Level 3, meaning it's twice as likely or three times as likely because of climate change," he said. 

Such events, he said, "really signal how unusual this heat is, how there's a really strong tie to carbon pollution in the atmosphere."

These catastrophic climate shifts are spiking hospitalizations and hitting vulnerable populations hardest, causing higher death tolls among marginalized communities and certain ethnic groups.