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For the first time, scientists have quantified the causal links between worsening heat waves and global warming pollution from individual fossil fuel and cement companies, pushing the boundaries of extreme weather event research in multiple surprising ways.
The new study, published Wednesday in the journal Nature, looks at a far more expansive series of heat waves than previous research. It also incorporates the causes of climate change into the calculations.
Instead of looking at one or two localized extreme heat events, the new study encompasses 213 heat waves around the world from 2000 to 2023. It finds, not surprisingly, that heatwaves became much more likely and severe during that period, largely due to the burning of fossil fuels.
Between the first and second decade that the researchers investigated, climate change made the heatwaves climb from being 20 times more likely to 200 times more likely, according to lead author Yann Quilcaille, a climate researcher at ETH Zurich.
Of the extreme heat events the researchers focused on, as many as a quarter of them would have been “virtually impossible” without the climate pollution from any of the 14 biggest “carbon majors” — the largest fossil fuel and cement producers responsible for the lion’s share of the world’s carbon pollution.
Even the smallest carbon major contributed to heat waves that would not have occurred without their climate pollution.
These so-called carbon majors include oil companies such as ExxonMobil and Chevron, as well as entire nations that have historically been significant fossil fuel producers, such as the former Soviet Union. CNN has contacted ExxonMobil and Chevron for comment on the study’s findings.
The study also found these companies are responsible for 50% of the increase in heat wave intensity since before humans started adding so much planet-warming carbon and methane pollution to the atmosphere.
In other words, the scientists found, the pollution from the biggest fossil fuel companies and nations made these severe and oftentimes deadly heat waves worse or even possible. The conclusions may have far-reaching ramifications, including aiding those who seek in court to make oil and gas companies pay for climate change-related harm, a task that has proven extremely difficult in the US.
There have been a growing number of studies in the past several years looking at the influence of global warming on individual extreme weather events, as well as other studies that have looked at the contribution of carbon majors to global warming. Wednesday’s study uses peer reviewed techniques from previous work and connects them in novel ways, Quilcaille and other scientists said.
“We establish that the fossil fuel and cement producers substantially contribute to these heatwaves,” Quilcaille said in an email. “We clearly quantify the causal link from their emissions to the intensity and the probability of occurrence of the heatwaves.”
The study found that compared to the climate prior to the industrial revolution, climate change has increased the median intensity of heatwaves by 3.02 degrees Fahrenheit (1.68 degrees Celsius) between 2010 and 2019, of which 0.85 degrees Fahrenheit (0.47 Celsius) was due to the top 14 carbon majors alone.
The other 166 carbon majors contributed 0.68 degrees Fahrenheit (0.38 degrees Celsius) of the heightened median intensity of heatwaves during the same period, the study found.
However, the report could be under-counting heat waves in Africa and South America, since they often go unreported, said Clair Barnes, a climate scientist at the Grantham Institute at Imperial College in the UK, who was not involved in the research.
“While it does give a clear picture of the effect that fossil fuel emissions are having on temperatures around the world, the true impacts are probably much worse,” Barnes told CNN.
Kristina Dahl, vice president for science at Climate Central, the nonprofit research and communications group, also said the new study, which she was not involved in, is novel.
“This is a really unique contribution, and it’s also a sweeping contribution,” Dahl said. “They’ve looked at a couple hundred heat waves here. And heat waves that were chosen in particular because they were impactful. So I think this is a really compelling piece of work that connects some dots that haven’t been connected before.”
By tying increasingly severe and common heat waves to specific companies, the new research could find its way into courtrooms where individuals, cities, states and countries are seeking to hold fossil fuel producers accountable for climate damages.
To that end, the author team includes a legal expert, which is somewhat unusual for a climate study.
“Courts are indicating a willingness to hold carbon majors accountable, but at the same time asking for more scientific certainty, and our study helps to close a part of that gap,” said Corina Heri, a study coauthor and law professor at Tilburg Law School in Zurich.
The research could help sort out the questions of who is at fault for contributing significantly to a particular heat wave, said study coauthor Richard Heede of the Climate Accountability Institute. Future studies could look at other types of extreme weather events, such as floods and wildfires, he said in a statement.
“In our study, we are providing early clues as to the impact of individual fossil fuel companies across their value chain from extraction, processing, distribution, and ultimate combustion of carbon fuels as intended by their global consumers,” Heede said.
“This study helps lay the foundation of who is at fault, and how to share responsibility.”