World’s Largest Fossil Fuel and Cement Producers Are Responsible for About Half the Intensity of Recent Heat Waves, New Study Shows

Carbon emissions generated by the world’s 180 largest fossil fuel and cement producers have played a substantial role in driving dangerous and oftentimes deadly extreme heat events around the world, according to new research. 

A study published Wednesday in the journal Nature finds that these emissions from the so-called carbon majors contributed to about half of the increase in intensity of heat waves compared to the preindustrial era. They have also contributed to significant increases in the likelihood of extreme heat events, including some that would have been virtually impossible without climate change. 

Led by researchers at the university ETH Zurich in Switzerland, the study examined the influence of climate change on over 200 heat waves around the globe from 2000 to 2023. It also looked at how the carbon majors contributed to these heat waves, finding that they played a significant role in their occurrence.

The latter analysis involves what is known as source attribution. In climate research, that means attributing global warming and its impacts to specific emissions sources. Researchers calculate the carbon emissions attributable to the carbon majors using data on company operations and sold products and associated emissions factors for carbon dioxide and methane. Those emissions figures are then used in climate models (comparing scenarios with and without observed warming) to analyze how the emitting companies contributed to increased warming.

Scientists are also able to pinpoint the influence of human-caused climate change on specific extreme weather events. This study combines those two approaches. It is one of the first to systematically analyze the impact that emissions from specific companies have had on multiple extreme weather events, in this case extreme heat, over a particular time period.

Researchers say their results are especially relevant for informing climate accountability initiatives such as litigation and that the study helps fill an evidentiary gap that may assist in establishing legal responsibility for climate harms. 

“We can expect this research will be quite relevant in a legal context,” Sonia Seneviratne, head of the Institute for Atmospheric and Climate Science at ETH Zurich, told Inside Climate News. 

The study employed peer-reviewed research methods that scientists use to examine the role that human-caused climate change played in amplifying individual extreme weather events, known as extreme event attribution. But rather than focus on a singular event, the researchers analyzed 213 heat waves reported in the international disaster database EM-DAT. 

“That helps us gain a more robust perspective on this link between climate change and heat waves,” Yann Quilcaille, a postdoctoral researcher at ETH Zurich and study lead author, explained. 

Using observed changes in global mean surface temperature, the researchers used statistical assessments and modeling to link global warming to increasing intensity and frequency of heat waves. Their results show that climate change has made the heat waves both hotter and much more likely to occur. 

According to the study, “the median estimates for the changes in intensity range across events from +0.3 °C to +2.9 °C,” with the higher figure in that range applicable to the 2021 Pacific Northwest heat dome. In the years 2020 to 2023, heat wave intensity increased by over 2°C (median estimates) due to climate change. In terms of probability, climate change has made heat waves about 20 times more likely between 2000 and 2009, and 200 times more likely between 2010 and 2019, compared to the preindustrial era. 

Researchers then extended the analysis to quantify the contributions of the carbon majors to these 213 heat waves. Collectively, these fossil fuel and cement producers are responsible for the majority of anthropogenic CO2 equivalent emissions from 1850 to 2023. Previous source attribution climate research has found that about half of the Earth’s surface warming and approximately one-third of the rise in sea levels can be traced to the emissions of the carbon majors. 

The new study demonstrates that these emissions have also contributed to the increasing intensity and probability of heat waves. 

“We already have observations for what is the temperature of the planet and how it evolves over time,” Quilcaille explained. “Then we assess what would be the difference if we were to remove emissions from individual carbon majors. That difference goes into the statistical model to deduce the change in probability and intensity, and thus the contribution of the carbon major, to the heat wave.”

Specifically, emissions from the carbon majors are responsible for about half of the roughly 1.7 degrees Celsius increase in intensity over the period 2010 to 2019 that can be attributed to climate change. The top 14 carbon majors contributed to about 28 percent of that increase, while the other 166 entities contributed to 22 percent of it. “These results show that the emissions of carbon majors contributed to about half of the increase in intensity of heat waves since preindustrial times, and that this contribution is rising,” the study states. 

Carbon majors are also making heat waves more likely to occur, the research suggests. “Depending on the carbon major, their individual contribution is high enough to enable the occurrence of 16–53 heat waves that would have been virtually impossible in a preindustrial climate,” the study explains. Even the emissions from the smallest carbon major contributed to more than a dozen heat waves that would have been virtually impossible absent climate change. 

“While the 14 largest carbon majors have contributed the most to the occurrence of heat waves, the contributions of smaller players also play a significant role,” Quilcaille said. 

The results are broadly consistent with another study published earlier this year in Nature, which went even further in quantifying economic damages resulting from intensifying heat waves that are linked to the emissions of the carbon majors. That study suggested that 111 carbon majors are responsible for $28 trillion in global economic losses stemming from extreme heat over the period 1991 to 2020. 

“We show that emissions traceable to carbon majors have increased heat wave intensity globally, causing quantifiable income losses for people in subnational regions around the world,” the study, authored by researchers Christopher Callahan and Justin Mankin, states. 

Mankin said the results of the new study by Quilcaille and colleagues are not surprising. “If you have made contributions to emissions, you have made contributions to extreme heat,” he told Inside Climate News. “But empirically showing that, as we did and now these authors have done, is crucial.”

Callahan agreed that the new study adds value as it, along with other studies, can strengthen the evidence base that informs discussions around corporate climate liability. 

“It is only over the last few years that this emitter-specific attribution, or ‘source attribution’, has been performed, and the new paper is a very important contribution to that effort,” Callahan said. “Together, these research efforts are building a credible and consensus-based body of work that provides scientific support for climate accountability.”

Litigation is already underway in the United States attempting to hold carbon majors such as ExxonMobil, Chevron, and Shell liable for climate damages and alleged deception. Two of the lawsuits focus specifically on harms from the 2021 Pacific Northwest heat dome, which resulted in hundreds of deaths and billions of dollars in damage. 

In 2023, Oregon’s Multnomah County brought a lawsuit against major fossil fuel companies as well as several of their trade associations and the consulting firm McKinsey & Company, seeking to recover over $50 billion in damage and adaptation costs. And on May 29 this year, the family of a woman in Washington State who died during the heat dome filed a first-of-its-kind wrongful death case against ExxonMobil and several other large oil companies. 

Quilcaille said it is clear that climate change, and the emissions of large carbon emitters, played a substantial role in this extreme heat event. “Climate change had a very strong influence on the Pacific Northwest heat wave,” he told Inside Climate News. “Not all carbon majors made that heat wave possible. But the big ones, yes. And each one of them substantially contributed to its probability and intensity.”

Inside Climate News reached out to ExxonMobil, Shell, Chevron and the American Petroleum Institute for comment. 

Extreme heat is the deadliest type of weather-related hazard. Another new study published Wednesday finds that nearly 1,700 heat-related deaths in Zurich, Switzerland, between 1969 and 2018 are attributable to human-induced climate change. The study also estimates that the carbon emissions of the six highest-emitting investor and state-owned companies globally caused, on average, at least one additional death per summer in Zurich since 2004. 

“Research like this forms an increasingly strong evidentiary basis for growing numbers of climate lawsuits filed in courts around the world,” said Rupert Stuart-Smith, deputy director of the Oxford Sustainable Law Program at the University of Oxford and lead author of the study.

Beyond the relevance of this type of research for legal proceedings, Quilcaille said that it could also have broader significance in informing policies around climate and energy. “This work is just one more reminder for decisionmakers that we need to phase out fossil fuels as soon as possible,” he said.