According to the latest study calculating the human cost of climate change, more than a third of the world’s heat deaths each year are directly attributable to global warming.
However, scientists say this is only a fraction of the total burden from the climate – even more people are dying from other extreme weather conditions exacerbated by global warming, such as storms, floods, and droughts – and the heat death toll will increase exponentially as temperatures rise .
Dozens of researchers who studied heat deaths in 732 cities around the world between 1991 and 2018 calculated that 37 percent were caused by higher temperatures due to man-made warming, according to a study published Monday in the journal Nature Climate Change.
That’s about 9,700 people a year from these same cities, but there are many more worldwide, said the study’s lead author.
“These are heat-related deaths that can actually be prevented. It’s something that we cause directly, ”said Ana Vicedo-Cabrera, epidemiologist at the Institute for Social and Preventive Medicine at the University of Bern in Switzerland.
The highest percentage of heat deaths caused by climate change were in cities in South America. Vicedo-Cabrera pointed to southern Europe and South Asia as further hot spots for heat deaths caused by climate change.
São Paulo, Brazil, has the highest number of climate-related heat deaths, averaging 239 per year, researchers found.
About 35 percent of heat deaths in the United States are due to climate change, according to the study. That adds up to more than 1,100 deaths a year in about 200 US cities, topped by 141 in New York. Honolulu had the highest proportion of heat deaths attributable to climate change at 82 percent.
Scientists used decades of mortality data in the 732 cities to draw curves detailing how each city’s death rate changes with temperature and how the heat-death curves differ from city to city. Some cities adapt to heat better than others due to air conditioning, cultural factors, and environmental conditions, Vicedo-Cabrera said.
Then the researchers took the observed temperatures and compared them to 10 computer models that simulate a world without climate change. The difference lies in the warming caused by humans. By applying this scientifically recognized technique to the individualized heat-death curves for the 732 cities, the scientists calculated additional heat deaths due to climate change.
“People continue to demand evidence that climate change is already affecting our health. This attribution study answers that question directly using state-of-the-art epidemiological methods, and the amount of data the authors have collected for analysis is impressive, ”said Dr. Jonathan Patz, director of the Global Health Institute at the University of Wisconsin.
Patz, who did not participate in the study, said it was one of the first to detail heat-related deaths related to climate change now and not in the future.