Carbon emissions from the world’s biggest fossil fuel companies have been directly linked to dozens of deadly heatwaves for the first time, according to a new analysis. The research has been hailed as a “leap forward” in the legal battle to hold big oil accountable for the damages being caused by the climate crisis.
The research found that the emissions from any one of the 14 biggest companies were by themselves enough to cause more than 50 heatwaves that would otherwise have been virtually impossible. The study shows, in effect, that those emissions caused the heatwaves.
The carbon pollution from ExxonMobil’s fossil fuels, for example, made 51 heatwaves at least 10,000 times more likely than in an unheated world, the researchers found, as did the emissions from Saudi Aramco.
Global heating is making heatwaves more frequent and more intense across the globe, contributing to at least 500,000 heat-related deaths a year. The searing heatwave that struck the Pacific Northwest of the US in 2021 was made almost 3C hotter, for example.
The new research found that the total emissions from the 180 “carbon major” companies included in the analysis were responsible for about half the increase in intensity, with emissions due to forest destruction making up most of the rest. It also found that the 213 heatwaves studied became 200 times more likely on average from 2010 to 2019 due to the climate crisis.
“Being able to trace back the contribution of these single [carbon major] emitters and quantify their contribution could be very useful for establishing potential liability,” said Prof Sonia Seneviratne, at ETH Zurich university in Switzerland, a senior author of the new report.
Dr Davide Faranda, a research director at the French National Centre for Scientific Research (CNRS) and not part of the study team, said: “This study adds a crucial new step: it connects the dots between specific climate disasters and the companies whose emissions made them possible. This bridge could become a cornerstone for legal and policy action to hold polluters accountable.”
Cassidy DiPaola, a spokesperson for the Make Polluters Pay campaign, said: “We can now point to specific heatwaves and say, ‘Saudi Aramco did this. ExxonMobil did this.’ When their emissions alone are triggering heatwaves that wouldn’t have happened otherwise, we’re talking about real people who died, real crops that failed, and real communities that suffered, all because of decisions made in corporate boardrooms.”
The world’s highest court, the International Court of Justice, ruled in July that failing to prevent climate harm could result in having to pay compensation, while a German high court set a legal precedent in May that fossil fuel companies could be held liable for their contribution. “Here’s the evidence the courts have been waiting for,” said DiPaola. “The bill is coming due, and it’s time these polluters pay for the damage they’ve done.”
The research, published in the journal Nature, used a type of analysis called attribution. This compares the hotter world today with the world before mass burning of fossil fuels to assess how emissions have driven up temperatures, using weather data and computer models.
The scientists first worked out how much each carbon major’s emissions had pushed up temperatures and then how much these higher temperatures increased the likelihood of heatwaves. Previous research has linked hundreds of individual events to global heating, but this study is the first to systematically analyse a series of events.
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“Climate change has made each of the 213 heatwaves more likely and more intense, and the situation has worsened over time,” said Dr Yann Quilcaille, at ETH Zurich and the lead author of the study.
The research found the increase in average intensity of the heatwaves rose from 1.4C in 2000-09 to 2.2C in 2020-23. The 213 major heatwaves assessed happened from 2000 to 2023 and spanned every continent. The data on them was taken from the biggest disaster database, EM-DAT, but Africa and South America were significantly underrepresented due to lack of reporting and suitable weather data.
“The study’s findings likely underestimate the true scale of these events, and the real consequences are probably far greater,” said Dr Friederike Otto, at Imperial College London.
Even the emissions from the fossil fuel companies at the bottom of the list of carbon majors had a significant impact on heatwaves. The carbon pollution from each of these caused 16 heatwaves to become at least 10,000 times more likely than before the climate crisis.
“This study is a leap forward that could be used to support future climate lawsuits,” said Dr Karsten Haustein, at the University of Leipzig, Germany, and not part of the study team. “It is also a reminder that denial and anti-science rhetoric will not make climate liability go away.”
Carbon emissions are emitted when people use oil, gas or coal to heat their homes or power their transport, but Quilcaille said fossil fuel companies had a particular responsibility – they had pursued profit through disinformation and lobbying, despite having known since the 1980s that burning fossil fuels would lead to global heating.
However, no polluter had yet been held accountable in court and challenges remained, said Prof Michael Gerrard and Dr Jessica Wentz, of the Sabin Center for Climate Change Law at Columbia University.
“The problem is the various legal issues that must be resolved before scientists can take the witness stand,” they said in a commentary in Nature. The issues included which courts should hear the cases, whether fossil-fuel producers should be liable for their customers’ emissions, and if long campaigns of deception by some fossil fuel companies were relevant, they said.
“The new study is one more building block, and a useful one, but the road to actual liability for the carbon majors is still littered with legal and evidentiary potholes,” they said.
ExxonMobil and Saudi Aramco did not respond to requests for comment.
