Climate Change Is Responsible for 37% of Heat Deaths

The climate crisis leaves more people vulnerable to heat waves than ever before.

A girl directs the spray from an open fire hydrant as children try to cool off from the summer heat August 7, 2001 in the Brooklyn borough of New York City.
New York City has a 44.2% rate of climate-caused heat deaths, according to a new study.

Spencer Platt/Getty Images

Heat waves are one of the most dangerous kinds of extreme weather events, and several studies have warned that they will become even deadlier as the climate warms.

Now, a first-of-its-kind study published in Nature Climate Change reveals that this prediction has already come true. Temperatures inflamed by the climate crisis have killed more people in the last three decades than would have died if we had never started pumping greenhouse gasses into the atmosphere, to a significant degree.

“One of three deaths due to heat can be attributed to the human activities driving climate change,” study first author Dr. Ana M. Vicedo-Cabrera, from the University of Bern, tells Treehugger in an email. 

Excess Deaths

The new study marks the first “large-scale, systematic effort to quantify the heat-related human health impacts that have already occurred due to climate change,” as the study authors put it. 

The researchers, from the University of Bern and the London School of Hygiene & Tropical Medicine (LSHTM), used data from 732 locations in 43 countries in order to conduct what is known as a “detection and attribution study,” according to an LSHTM press release.

This is a kind of study that works to isolate certain impacts—in this case, deaths caused by temperatures higher than the ideal for human health in a certain location—and link them to changes in climate or weather.

“We estimated heat-related mortality in two climate scenarios—under current conditions or removing the anthropogenic activity—and computed the difference, considering this the contribution of the human activities to climate change,” Vicedo-Cabrera tells Treehugger. 

The results told the researchers that around 37% of the excess heat deaths during the summers between 1991 and 2018 could be directly attributed to human-caused climate change. This impact was felt on every continent, though some regions and cities were more impacted than others. Regionally, Central and South America were the most impacted, followed by South East Asia. 

The researchers were also able to determine the annual number and overall percentage of climate-caused heat deaths for several major cities:

  1. Santiago, Chile: 136 extra deaths per year, or 44.3% of the total
  2. Athens: 189 extra deaths, or 26.1%
  3. Rome: 172 extra deaths, or 32%
  4. Tokyo: 156 extra deaths, or 35.6%
  5. Madrid: 177 extra deaths, or 31.9%
  6. Bangkok: 146 extra deaths, or 53.4%
  7. London: 82 extra deaths, or 33.6%
  8. New York City: 141 extra deaths, or 44.2%
  9. Ho Chi Minh City: 137 extra deaths, or 48.5%

However, while the study could pinpoint differing impacts across regions and cities, it did not examine why those differences occurred. 

Tourists fill bottles of water in a fountain at Piazza del Pantheon as temperatures rise in 2015 in Rome, Italy.
Tourists fill bottles of water in a fountain as temperatures rose in 2015 in Rome, Italy. Giorgio Cosulich/Getty Images

Past and Future

The new study builds on a larger body of work that has been published by the Multi-Country Multi-City (MCC) Collaborative Research Network in an attempt to understand the relationship between health, climate, and other environmental problems like air pollution. 

When it comes to the group’s previous work on climate, health, and heat, most of it has focused on the future. A 2017 study published in The Lancet Planetary Health found that heat-related deaths would increase through the end of 2100 if humans continue to emit greenhouse-gas emissions at high levels. A 2018 study published in Climatic Change found that limiting global warming to the Paris agreement goal of two degrees Celsius above pre-industrial levels would prevent “large increases” in heat-related deaths around the world. 

But the most recent study, co-author, MCC coordinator and LSHTM professor Antonio Gasparrini tells Treehugger, “provides another layer of perspective.”

“You don’t have to wait until . . . 2050 to see these effects,” Gasparrini says. “They are already here.”  

For Gasparrini, Vicedo-Cabrera and their team, this is not an excuse to throw in the towel on fighting climate change. Just the opposite, in fact. Gasparrini argues that the future death toll could be much higher if nothing is done to combat the climate crisis.

“It underlines the importance of acting quickly on preventing these impacts,” he says.

How to Act

When it comes to action, Gasparrini calls for two types of policies:

  1. Mitigation
  2. Adaptation

Mitigation means reducing emissions by decreasing consumption or switching to cleaner sources of energy. Adaptation means understanding what factors make some populations more vulnerable to heat waves than others and working to counteract them. 

Because of feedback loops, a certain amount of warming is inevitable in the next few decades even if emissions are immediately reduced. Because of this, it is important to understand which factors, such as socio-economic status, infrastructure or behavior, put people at greater risk during heat waves. 

“The idea is to try to understand these mechanisms a bit better in order to shape ...policies that can be effective in decreasing the risk for a given climate,” Gasparrini explains. 

Currently, more research needs to be done to understand which interventions would save the most lives. Air conditioning is effective, but is counterproductive when it comes to mitigating climate change. Other changes could include improving insulation or increasing tree cover in cities.

“It’s still an active area of research,” Gasparrini says. 

View Article Sources
  1. "Heat Waves." World Health Organization.

  2. Vicedo-Cabrera, A. M., et al. "The Burden of Heat-Related Mortality Attributable to Recent Human-Induced Climate Change." Nature Climate Change, vol. 11, no. 6, 2021, pp. 492-500., doi:10.1038/s41558-021-01058-x

  3. "Global warming already responsible for one in three heat-related deaths." London School of Hygiene and Tropical Medicine, 2021.

  4. Vicedo-Cabrera, Ana Maria, et al. "Temperature-Related Mortality Impacts Under and Beyond Paris Agreement Climate Change Scenarios." Climatic Change, vol. 150, no. 3-4, 2018, pp. 391-402., doi:10.1007/s10584-018-2274-3