Systematic attribution of heatwaves to the emissions of carbon majors

Extreme event attribution assesses how anthropogenic climate change affected an extreme climate event, but typically focuses on individual events. Here, we systematize this approach, and apply it to 187 historical heatwaves reported over the period 2000-2022. We show that climate change has made all these heatwaves more likely and more intense. In particular, 33% of these heatwaves were virtually impossible without anthropogenic influence. Furthermore, this influence rises over time, both in intensity and in likelihood: climate change made the median heatwaves 24 times more likely over 2000-2009, 293 times more likely over 2010-2019 and 1355 times more likely over 2020-2022. We also extend the attribution to the contribution of emitters, by quantifying how much these heatwaves were affected by the emissions of 122 carbon majors (fossil fuel and cement producers), assessed through their full value chain. Our best estimate shows that, depending on the carbon major, between 28 and 62 heatwaves have been made 10,000 times more likely. Even small carbon majors enable heatwaves with their sole contribution.