Photograph by Matthieu Croizier / Connected Archives
WORDS BY HUMBERTO BASILIO
One hundred and eighty of the world’s largest oil, gas, coal, and cement producers are collectively responsible for the heat waves that have killed hundreds of thousands of people over the past two decades. A new study published today in Nature has, for the first time, directly tied hundreds of heat waves to these so-called carbon major entities.
Although communities and activists have long pointed to these entities’ role in driving extreme heat, few judicial cases have held any company accountable. Courts often dismiss lawsuits for lack of evidence. This new study provides crucial data that could help make justice possible.
The carbon majors “have long claimed that the impacts of climate change are too far removed from emissions for any principle of accountability to apply,” said climate scientist Dr. Christopher Callahan at Indiana University Bloomington, who was not involved in the research. This study, he said, “shows that that claim is false.”
Until recently, extreme weather attribution has mostly focused on single disasters. Such studies typically assess whether climate change made a given event more likely, but they do not identify who was responsible for the emissions that drove those changes.
That gap is what led climate scientist Dr. Yann Quilcaille and his team from the Swiss Federal Institute of Technology Zurich to look for the culprits.
By tracing emissions back to their producers, Quilcaille said, attribution science can support communities seeking damages or stronger climate action. “We didn’t have that information before,” Quilcaille said. “Now we do.”
“The analysis showed that, compared with preindustrial conditions, climate change made heat waves 20 times more likely between 2000 and 2009, and up to 200 times more likely between 2010 and 2019.”
The new study examined 213 heat waves that took place across 63 countries between 2000 and 2023, all of which caused significant human or economic losses. The researchers compared the probability and intensity of each heat wave under today’s conditions with a hypothetical scenario in which global temperatures remained at preindustrial levels. The analysis showed that, compared with preindustrial conditions, climate change made heat waves 20 times more likely between 2000 and 2009, and up to 200 times more likely between 2010 and 2019.
The researchers then compiled historical records to estimate emissions dating back to the mid-19th century for 180 carbon majors, including 174 companies like ExxonMobil and six nation-state producers like China. Using simulations, they approximated how much heat could be linked to each entity. For instance, they found that emissions from the former Soviet Union made 53 heat waves since 2000 at least 10,000 times more likely. Even the smallest emitter in the database, a Russian coal company called Elgaugol, made 16 heat waves possible that otherwise would have been virtually impossible.
Climate change on average has made heat waves 2.2 degrees Celsius hotter—or 3.9 degrees Fahrenheit—the study finds, and half of that can be attributed directly to carbon majors. The 14 biggest entities, including ExxonMobil, Shell, and China’s coal industry, were responsible for about as much warming as all the other 166 carbon majors combined.
The results are “solid” and “make a good job connecting the dots” that are necessary to hold companies accountable, said Dr. Kristina Dahl, vice president for science at the nonprofit Climate Central. These types of studies can be used as evidence in court cases. For example, a county in Oregon sued ExxonMobil and other firms in 2023 for their role in worsening the 2021 Pacific Northwest heat wave.
“Attribution science is an important part of these cases by showing that there is a direct connection between greenhouse gas emissions and local climate change impacts.”
“Attribution science is an important part of these cases by showing that there is a direct connection between greenhouse gas emissions and local climate change impacts,” Callahan said. Yet so far, none of these lawsuits has been resolved, and they are advancing slowly.
In April 2025, Callahan published a study in Nature showing that emissions linked to oil giant Chevron likely caused between $791 billion and $3.6 trillion in heat-related losses between 1991 and 2020. Still, he said, “we are years away from a successful damages case against a fossil fuel producer.”
Another major barrier to reparations in the U.S. is the rollback of climate policy under President Donald Trump. His administration recently announced plans to revoke the EPA’s 2009 endangerment finding, the longstanding determination that greenhouse gases threaten public health and the legal foundation for federal climate regulation. If successful, the move could erase existing emissions limits on vehicles, factories, and power plants.
“Current decision-makers are not relying on the best available science to make those decisions,” Callahan said, “and are instead taking advantage of shoddy scientific work that downplays many of the risks of climate change.”
In response, researchers at the National Academies of Sciences, Engineering, and Medicine are conducting a rapid scientific review evaluating new evidence on climate change and health risks. The report will be published this month and aims to deliver conclusions that can endure political scrutiny and support existing climate protections.
“We live in a world that has been shaped by the fossil fuel industry,” Dahl said, “If we want to minimize future harms from that warming, we need to be steeply and drastically cutting our carbon emissions.”
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New Study Links 174 Companies to Deadly Heat Waves
