Overview

• Scientists analyzed 213 heatwaves from 2000–2023 and found every event was made more likely and more intense by human-caused warming, with 55 deemed virtually impossible without it.
• Emissions traced to 180 major fossil fuel and cement producers account for about 57% of historical CO2 and contributed to roughly half of the increase in heatwave intensity since preindustrial times.
• The influence of warming on heatwaves grew sharply over time, making such events about 20 times more likely in 2000–2009 and about 200 times more likely in 2010–2019 compared with preindustrial conditions.
• The study quantifies impacts for marquee events, including the 2021 Pacific Northwest heat dome, which was about 2.3°C hotter and more than 10,000 times more likely, with 619 deaths reported in British Columbia.
• Researchers used established attribution methods and the EM-DAT disaster database, assigned full value-chain emissions to producers, noted likely undercounting in the Global South, and reported that industry groups contest end‑use attribution.