Half of the increase in heat wave intensity since pre-industrial times can be traced to the greenhouse gas emissions from just 180 fossil fuel and cement producers, according to a new study. Each of these entities has emitted enough greenhouse gases to cause multiple heat waves that would have been virtually impossible in the absence of climate change.
The analysis represents an advance in attribution science, a growing field that assigns and quantifies the contributions of different causes to climate change and extreme weather events. It’s become clear from these analyses that climate change is making heat waves worse.
But most previous studies in this area have looked at one heat wave or other extreme event at a time, and they have rarely broken down the contribution of individual nations or corporations. This is the first study to systematically analyze the contributions of multiple actors to multiple events.
Researchers assembled information from the International Disaster Database on 226 heat waves that occurred between 2000 and 2023 across all 7 continents. Although there were few entries from Africa, South America, and the Caribbean, an advantage of the database is that it uses a consistent methodology to define and report on disasters that cause significant casualties, economic losses, or governmental disaster declarations. The researchers calculated how overall climate change affected the likelihood and intensity of each heat wave.
They also gathered data on cumulative emissions from 1854–2023 of 180 “carbon majors” – the world’s largest emitters, which include investor-owned companies such as ExxonMobil, state-owned companies such as Saudi Aramco, and nation-state producers such as the former Soviet Union.
Next, the researchers calculated the contribution of the individual carbon majors to climate change by subtracting the emissions of each one in global climate models. Once they knew the fraction of global average temperature change attributed to each carbon major, they could calculate the fraction of change in the probability and severity of each heat wave due to each one.
Human-caused climate change increased the likelihood and intensity of 213 heat waves that occurred worldwide between 2000 and 2023, the researchers report in the journal Nature.
Heat waves are worse now than they were in the past, and the influence of climate change on heat waves is increasing. Climate change made heat waves 20 times more likely in 2000-2009 compared to 1850-1900, the researchers calculated. Between 2010 and 2019 heat waves were up to 200 times more likely.
About one-quarter of the individual heat waves – 55 of them – were made 10,000 times more likely by climate change. In other words, they would have been virtually impossible in a pre-industrial climate.
Meanwhile, the 180 carbon majors are responsible for 60% of total human-caused emissions from 1850-2023. About half of the increase in global average temperature and half of the increase in heat wave intensity can be attributed to them.
The 14 largest emitters have made approximately the same contribution to climate change as the other 166 carbon majors. Each of these 14 entities has emitted enough greenhouse gases to cause more than 50 heat waves.
Even the smallest carbon major, the Russian coal company Elgaugol, produced enough emissions to cause 16 heat waves.
“These results are relevant not only in the scientific community but also for climate policy, litigation and wider efforts concerning corporate accountability,” the researchers write.
By tracing the chain of causality back from extreme events to climate change to individual emitters, the analysis could contribute to a legal basis for establishing responsibility for heat waves and implement the “polluter pays” principle.
The researchers plan to investigate other extreme events such as heavy rainfall, droughts, and fires in a similar way.
Source: Quilcaille Y. et al. “Systematic attribution of heat waves to the emissions of carbon majors.” Nature 2025.
Image: © Anthropocene Magazine.
