More than a third of summer heat-related fatalities are due to climate change, researchers said on Monday, warning of even higher death tolls as global temperatures climb.
Previous research on how climate change affects human health has mostly projected future risks from heat waves, droughts, wild fires and other extreme events made worse by global warming.
How much worse depends on how quickly humanity curbs carbon emissions, which hit record levels in 2019 but dipped sharply during the pandemic.
But a new study by an international team of 70 experts is one of the first — and the largest — to look at health consequences that have already happened, the authors said.
On average, 37 percent of all heat-related deaths can be attributed directly to global warming.
“Climate change is not something in the distant future,” senior author Antonio Gasparrini, a professor of biostatistics and epidemiology at the London School of Hygiene and Tropical Medicine, said.
“We can already measure negative impacts on health, in addition to the known environmental and ecological effects.” The authors said their methods — if extended worldwide — would add up to more than 100,000 heat-related deaths per year laid squarely at the feet of manmade climate change.
That number could be an underestimate because two of the regions for which data was largely missing — south Asia and central Africa — are known to be especially vulnerable to extreme heat deaths.
The 100,000 figure is consistent with a recent analysis from the Institute for Health Metrics and Evaluations (IHME), published in The Lancet.
IHME calculated just over 300,000 heat-related deaths worldwide from all causes in 2019. If just over a third of those deaths are due to climate change, as Gasparrini’s team reported, the global total would indeed be more than 100,000.
India accounted for more than a third of the total in the IHME tally, and four of the five worst-hit countries were in south Asia and central Africa.
The share of heat-related deaths attributable to global warming in the new study varied widely from country to country.
In the United States, Australia, France, Britain and Spain, for example, that percentage was roughly in line with the average across all countries, between 35 and 39 percent.
For Mexico, South Africa, Thailand, Vietnam and Chile, the figure rose above 40 percent.
And for half-a-dozen countries — Brazil, Peru, Colombia, the Philippines, Kuwait and Guatemala — the percentage of heat-related mortality caused by climate change was 60 percent or more.
A complex methodology combining health data and temperature records from 1991 to 2018, coupled with climate modeling, allowed researchers to contrast the actual number of heat-related deaths with how many fewer deaths there would have been without manmade warming.