Study: 25% of recent heatwaves 'virtually impossible' without man-made climate change

Human activity responsible for climate change has led to more than 50 heat waves since the year 2000, scientists say.

According to a new study published in the journal Nature, just over a quarter of all heat waves in the last 25 years would have been “virtually impossible” without human-caused climate change.  

Professor Sonia Seneviratne is a climate scientist at ETH Zurich University and one of the authors of the study:  

"So we looked at the range of heat waves that happened recently, and we looked at how much more probable they were made because of those emissions of the carbon majors. And what we find is that for many events, they were made clearly much more probable," she said. 

The set of heat waves in the study came from the EM-DAT International Disaster Database, which the researchers described as the most widely used global disaster repository. The Nature study examined all of the heat waves in the database from 2000 to 2023 except for a few that weren’t suitable for their analysis. 

The study found that global warming made all 213 of the heat waves examined more likely. Out of those, 55 were 10,000 times more likely to have happened than they would have been before industrialisation began accelerating in the 1800s. They wrote that the calculation is equivalent to saying those 55 heat waves “would have been virtually impossible” without human-caused climate change. 

Individual contributions

The scientists also found that emissions from 180 major cement, oil and gas producers contributed significantly to all the heat waves.  

The study found that collectively these producers are responsible for 57% of all the carbon dioxide that was emitted from 1850 to 2023. 

"We find that even individual contributions are often sufficient to make some of those heat waves basically definitely much more probable," Seneviratne says. “It just shows that it’s not that many actors … who are responsible for a very strong fraction of all emissions.”

Those polluters identified include publically-traded and state-owned companies, as well as a few countries where fossil fuel production data was available at the national level. 

Climate scientists can use complex computer programs and historic weather data to calculate the connection between extreme weather events and the planet-warming pollutants humans emit. Climate change attribution studies often focus on how climate change influenced a specific weather event, but the scientists say this new Nature study is unique because they focus on the extent to which cement and fossil fuel producers have contributed to heat waves. 

Scientists say this study could be considered in legal cases. Globally, dozens of lawsuits have been filed against fossil fuel companies by climate activists, US states and others seeking to hold the companies accountable for their role in climate change. 

For example, Vermont and New York have passed laws that aim to hold fossil fuel companies accountable for their emissions and the damage caused by climate change. 

“For a while, it was argued that any individual contributor to climate change was making too small or too diffuse a contribution to ever be linked to any particular impact," said Chris Callahan, a climate scientist at Indiana University, who was not involved in the study. "And this emerging science, both this paper and others, is showing that that’s not true.”