The 2021 heat dome in the Pacific Northwest that overwhelmed emergency rooms and left hundreds dead. The 2022 heat wave in India that devastated the wheat harvest. The deadly heat waves in France in 2003, and China in 2013.
A new study links these recent heat waves — and more than 200 others — to human-caused climate change, and the greenhouse gas pollution of major fossil fuel producers.
The new study, published Wednesday in the journal Nature, found that 213 heat waves were substantially more likely and intense because of the activity of major fossil fuel producers, also called carbon majors. They include oil, coal and cement companies, as well as some countries.
The scientists found as much as a quarter of the heat waves would be "virtually impossible" without the climate pollution from major fossil fuel producers. Some individual fossil fuel companies, such as ExxonMobil, Chevron and BP, had emissions high enough to cause some of the more extreme heat waves, the research found.
"The main findings show clearly that the carbon majors play very important roles for those recent heat waves that were analyzed," says Sonia Seneviratne, climate scientist at ETH Zürich, a university in Switzerland, and one of the co-authors of the study.
"This is an important part of the equation," Seneviratne says, "to basically provide better quantification of their responsibility."
ExxonMobil, Chevron and BP did not respond to NPR's requests for comment.
The study adds to a growing body of research linking the emissions of fossil fuel companies to extreme weather events that have had catastrophic impacts for economies and human health.
At least 489,000 people died annually from heat between 2000 and 2019, according to the World Health Organization, many from climate-change fueled heat waves.
Climate researchers say as more and more states, cities and countries file suit against oil companies for climate-change related damages, studies attributing particular climate events back to particular corporations and countries could become more important in litigation.
"If you've contributed to emissions, you've contributed to extreme heat," says Justin Mankin, geography professor at Dartmouth College, who did not participate in the study but reviewed a copy of it.
"Being able to benchmark it to heat waves with a known societal impact — that's what I think is actually pretty important about this work," he says.
For the new study, the scientists looked at something called the disaster database, a global list of disasters maintained by university researchers, to identify heat waves with significant casualties, economic losses and calls for international assistance. The scientists then used historical reconstructions and statistical models to see how human-caused global warming made each heat wave more likely and more intense.
Then, to examine the link to major fossil fuel producers, the researchers relied on the Carbon Majors Database to understand the emissions of major oil, gas, coal and cement producers.
" We ran a climate model to reconstruct the historical period, and then we ran it again but without the emissions of a specific carbon major, thus deducing its contribution to global warming," Yann Quilcaille, climate scientist at ETH Zürich and lead author of the study, says in an email.
While some of the contributions to heat waves came from larger well-known fossil fuel companies, the study found that some smaller, lesser-known fossil fuel companies are producing enough greenhouse gas emissions to cause heat waves too, Quilcaille says.
Mankin says this study comes at an important time for climate policy in the United States. The Trump administration wants the government to stop regulating climate pollution.
The Environmental Protection Agency is proposing rolling back what's known as the endangerment finding, the basis for rules regulating climate pollution, including from coal and gas-fired power plants, cars and trucks, and methane from the oil and gas industry.
As federal agencies make the argument that greenhouse gases are not harmful to society, Mankin says research like this is important because it shows the opposite is the case.
Mankin says of the Trump administration: "They think these emissions don't actually have societal consequences and Yann's research and Sonia's research here shows — very clearly — that these emissions have an undeniable impact on society.
"It's a deleterious, harmful impact, enhancing the likelihood and magnitude of extreme heat."
The EPA declined to answer NPR's question about whether it acknowledges that greenhouse gases released from burning fossil fuels endanger public health. It said in an email that "the agency considered a variety of sources and information in assessing whether the predictions made, and assumptions used, in the 2009 Endangerment Finding are accurate."
It added: "The public comment period is currently open, and EPA looks forward to receiving them."
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