Europe's 2025 heat wave struck a decade after countries promised to curb warming, and new research indicates emissions after 2015 contributed to the event's intensity.
Here's what to know
A September 22 study published in Geophysical Research Letters said that there is better than a 99% chance emissions released in the decade after the 2015 Paris Agreement made Europe's deadly June 2025 heat wave worse.
The Stanford Doerr School of Sustainability reported (via Phys.org) that in some parts of Europe, post-2015 emissions lifted average daily temperatures by roughly a third of a degree Celsius — just over half a degree Fahrenheit.
The researchers reached their conclusions with a diffusion-model version of generative AI. After training it on 10 global climate models and checking it against decades of real-world weather data, they used it to compare the actual heat wave with a version of events in which emissions had stayed at 2015 levels.
Lead author Jared Trok, a Ph.D. student in Earth system science at the Doerr School of Sustainability, said, "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."
Trok added, "That result is not unique to the 2025 heat wave, but also true for Europe's hottest week in every individual year since at least 2021."
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More background
That conclusion is especially notable given what the Paris Agreement was supposed to represent. Under the 2015 pact, nearly 200 countries committed to keeping warming far below 2 degrees Celsius (3.6 degrees Fahrenheit) above preindustrial levels while also aiming for 1.5 degrees Celsius (2.7 degrees Fahrenheit).
Even so, nearly one-fifth of all carbon pollution has been released since 2015, according to the researchers, largely from oil, natural gas, and coal.
The study noted that even modest increases in daily temperatures can have outsized consequences — raising the risk of heat-related deaths, straining electricity demand, reducing labor productivity, and harming agricultural yields — during events like Europe's 2025 heat wave, which killed several thousand people.
What can be done?
The work could matter beyond climate science as thousands of lawsuits seek to hold fossil fuel companies accountable for climate-linked damages, and sharper attribution methods may help show how added emissions influence specific disasters.
As heat waves intensify, stronger local heat preparedness plans, resilient power systems, and household strategies for staying cool safely will become increasingly important.
Co-author Noah Diffenbaugh, the William Wrigley Professor and Kimmelman Family Senior Fellow at the Doerr School of Sustainability, warned, "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."
Where can I learn more?
These stories show how worsening heat is already reshaping life in Europe and straining the broader climate system.
• Across Europe, deadly heat is obliterating records, closing schools, and exposing public-health gaps.
• Forecasters say climate-driven summer heat is intensifying dangerous conditions across broad regions.
• Record May CO2 levels mean hotter summer conditions are becoming more likely worldwide.
• In France, rivers too warm for reactors cut nuclear output and lift prices.
• Scientists warn the hottest year on record underscored growing uncertainty in climate models.
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