More than a third of heat deaths worldwide each year are due directly to global warming, according to the latest study to calculate the human cost of climate change.
But scientists say that’s only a fraction of the global climate toll – even more people are dying from other extreme weather conditions amplified by global warming like storms, floods and drought – and the number of deaths. heat will increase exponentially with rising temperatures.
Dozens of researchers who examined heat deaths in 732 cities around the world between 1991 and 2018 calculated that 37% were caused by higher temperatures due to human-induced warming, according to a study published in the journal Monday. Nature Climate Change.
That’s about 9,700 people a year in these cities alone, but it’s much more global, the study’s lead author said.
“These are heat-related deaths that are actually preventable. This is something that we are causing directly, ”said Ana Vicedo-Cabrera, epidemiologist at the Institute of Social and Preventive Medicine at the University of Bern in Switzerland.
The highest percentages of heat deaths caused by climate change were found in cities in South America. Vicedo-Cabrera said southern Europe and South Asia were other hot spots for heat deaths linked to climate change.
São Paulo, Brazil, has the most climate-related heat deaths, averaging 239 per year, researchers say.
About 35% of heat deaths in the United States can be attributed to climate change, according to the study. This represents a total of more than 1,100 deaths per year in about 200 US cities, compared to 141 in New York. Honolulu had the highest share of heat deaths attributable to climate change, 82 percent.
Scientists used decades of death data from all 732 cities to plot curves detailing how each city’s death rate changes with temperature and how heat death curves vary from city to city. Some cities adapt better to the heat than others due to air conditioning, cultural factors and environmental conditions, said Vicedo-Cabrera.
Next, the researchers took the observed temperatures and compared them to 10 computer models simulating a world without climate change. The difference is the warming caused by humans. By applying this scientifically accepted technique to individualized heat death curves for the 732 cities, the scientists calculated the additional heat deaths due to climate change.
“People keep asking for evidence that climate change is already affecting our health. This attribution study directly answers that question using cutting-edge epidemiological methods, and the amount of data the authors have accumulated for the analysis is impressive, ”said Dr. Jonathan Patz, director of the Global Health Institute of the ‘University of Wisconsin. .
Patz, who was not part of the study, said it was one of the first to detail heat deaths linked to climate change now, rather than in the future.