The Sept. 22 paper in Geophysical Research Letters finds a >99% probability that greenhouse-gas emissions released after the 2015 Paris Agreement amplified Europe’s June 2025 heat wave. Using a diffusion-model generative AI trained on 10 global climate models and validated with decades of observations, researchers estimate post-2015 emissions raised daily averages in parts of Europe by about 0.33°C (~0.5°F). The authors warn similar effects appear for Europe’s hottest week each year since 2021 and say intensified heat extremes will increase deaths, strain power systems, and harm agriculture unless preparedness improves.
Study: Emissions Since 2015 Made Europe’s Devastating 2025 Heat Wave Worse
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A new analysis published Sept. 22 in Geophysical Research Letters finds that greenhouse-gas emissions released after the 2015 Paris Agreement significantly increased the intensity of Europe’s deadly June 2025 heat wave.
Key Findings
Researchers at the Stanford Doerr School of Sustainability report there is better than a 99% probability that post-2015 emissions made the 2025 event worse. In some parts of Europe, the team estimates those additional emissions raised average daily temperatures during the heat wave by roughly 0.33°C (about 0.5°F).
How the Study Was Done
The authors used a diffusion-model variant of generative artificial intelligence, trained on output from 10 global climate models and validated against decades of observational weather records. This approach let them compare the observed 2025 heat wave with a counterfactual scenario in which emissions remained at 2015 levels.
"We found strong evidence that if Europe’s heat wave in the summer of 2025 had occurred without the emissions since 2015, it very likely would have been cooler," said lead author Jared Trok, a Ph.D. student in Earth System Science at the Doerr School.
Co-author Noah Diffenbaugh, William Wrigley Professor and Kimmelman Family Senior Fellow at the Doerr School, added, "This study highlights that we can expect the kinds of extreme heat waves we've been experiencing recently to intensify even more in the coming years."
Consequences and Broader Context
Although the Paris Agreement in 2015 committed nearly 200 countries to limit warming well below 2°C and pursue efforts toward 1.5°C, the authors note that almost one-fifth of all historical carbon emissions have been released since 2015, primarily from burning oil, natural gas, and coal. Even modest increases in daily temperature during extreme events can cause outsized harms: higher risks of heat-related deaths, greater strain on electricity systems, reduced labor productivity, and losses to agricultural yields. The paper cites several thousand deaths during Europe’s June 2025 heat wave.
The study’s improved attribution methods also have legal and policy relevance: as thousands of lawsuits seek to hold fossil-fuel companies accountable for climate-linked damages, sharper techniques that quantify the role of added emissions in specific disasters may be influential in court and policymaking.
What Comes Next
As heat waves grow more frequent and intense, the authors and public-health experts emphasize the need for stronger local heat-preparedness plans, resilient power systems, and household strategies for safe cooling. The study adds to mounting evidence that current emissions trajectories are already amplifying the severity of climate extremes.
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