Climate change boosted heat deaths by more than a third: Study

Excess deaths from extreme heat were 37 per cent over what they would have been without the effects of climate change, with global warming expected to only get worse over the next century without serious action.

Extreme heat events aren’t just a matter of having a few uncomfortably warm days: they’re a real and recognized threat to public health, particularly for society’s most vulnerable.

Now, with global temperatures continuing to rise, a new study says heat-related deaths over the last three decades were 37 per cent over and above what they would have been without the effects of climate change.

“Burdens varied geographically but were of the order of dozens to hundreds of deaths per year in many locations,” the researchers wrote in their paper, published this month in Nature Climate Change. “Our findings support the urgent need for more ambitious mitigation and adaptation strategies to minimize the public health impacts of climate change.”

The study arrived at those figures by comparing two climate models: one factoring in global warming due to human emissions, and one without. It was based on temperature and mortality data collected from 732 locations across 43 countries over a 28-year period from 1991 to 2018.

The researchers point out that the 37 per cent estimate is an average, and the figure would vary from country to country — for parts of the Middle East, Southeast Asia, and Central and South America, heat-related deaths were at least 50 per cent higher than what they would have been without the effects of climate change.

Global warming has been on the rise since the industrial era, but has been accelerating in recent years. NASA says the per-decade average increase since 1880 was 0.08°C, more than doubling to 0.18°C from 1980 to the present. The 10 hottest years on record have all occurred since 2005, and 2020 came within a hair’s breadth of taking the top spot from 2016.

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In recent years, there’ve been several instances of large amounts of excess deaths that could be plausibly linked to individual extreme heat events. In August 2003, a heat wave in Europe was responsible for around 11,000 deaths in France alone, many of them seniors. In Montreal, a 2018 heat wave killed or hastened the deaths of 66 people, many of them among people with low income or social isolation, and triggered a public health investigation.

Many cities across Canada have extreme heat event protocols that open public cooling centres and employ other methods to reduce the risk to residents, but the researchers say more concerted action will be needed in the coming century.

"We expect the proportion of heat-related deaths to continue to grow if we don't do something about climate change or adapt," one of the lead authors, Dr. Ana Vicedo-Cabrera, said in a release from the University of Bern. "So far, the average global temperature has only increased by about 1°C, which is a fraction of what we could face if emissions continue to grow unchecked."

Even with efforts to limit future temperature rise, a certain amount of global warming is baked in at this point. Even the Intergovernmental Panel on Climate Change (IPCC), which advises governments on the science of climate change and recommends courses of action, doesn’t aspire to completely reverse the warming process: its current stated goals are to limit the warming to no more than 2°C above pre-industrial levels, and closer to 1.5°C if possible.

Canada, meanwhile, is actually warming twice as fast as the global average, and a study released last year by the Prairie Climate Centre offered a grim outlook on what that means for the kind of extended heat events that threaten public health.

The study found that, across most of Canada’s major cities, heat waves will be more frequent, last longer, and be slightly hotter on average than in previous decades, even in communities where they are relatively rare. In Ottawa, for example, heat waves could last at least 17 days by 2051–2080, up from the current average of four days. In Regina, the number of days that reach at least 34°C is expected to jump from three to at least 23 over the same period.

Thumbnail credit: David Bradley