The study, published in Geophysical Research Letters, finds that greenhouse gas emissions since the 2015 Paris Agreement have already increased the intensity of Europe’s recent heat waves. Using a generative AI diffusion model trained on data from 10 global climate models, researchers simulated how Europe’s hottest weeks from 2016–2025 would have unfolded under 2015 emission levels. They estimate the last decade’s emissions raised 2025 heat-wave intensity by about 0.33°C, a change that can meaningfully amplify health and infrastructure impacts. The authors warn that some further intensification of extremes is already committed despite future mitigation efforts.
A Decade of Emissions Has Already Made Europe’s Heat Waves Worse, Study Finds
A woman shelters from the sun with a parasol on June 21, 2026 in Seville, Spain. —Marcelo del Pozo—Getty Images
A new study published in Geophysical Research Letters finds that greenhouse gases emitted since the 2015 Paris Agreement have already measurably amplified the intensity of recent heat waves across Europe.
Study and Methods
Researchers led by Jared Trok of Stanford trained a generative AI diffusion model on simulated weather output from 10 global climate models. They forced the model with the observed atmospheric circulation patterns that produced Europe’s most intense annual heat weeks from 2016 through 2025—episodes typically associated with persistent high-pressure systems known as "heat domes." The team then simulated daily temperatures for each event under the emissions level present at the time and under a lower-emissions 2015 baseline.
Key Findings
The analysis shows that emissions released since 2015 increased the intensity of Europe’s 2025 heat waves by roughly 0.33°C (about one-third of a degree Celsius). The authors report that this influence is detectable for Europe’s hottest week in every year from at least 2021 through 2025. Surface air temperatures during recent events exceeded 40°C (104°F) across many countries and reached up to 46°C (114.8°F) in Spain and Portugal.
"We found that the emissions released since the signing of [the Paris Agreement] in 2015 have substantially and significantly increased the intensity of Europe's recent individual heat waves," says Jared Trok, lead author and PhD student in Earth system science.
The study also notes real-world consequences: this summer’s consecutive, record-breaking heat waves across Europe have been linked to at least 35,000 excess deaths, underscoring the human toll of even modest increases in extreme heat.
Why Small Increases Matter
Although an extra third of a degree may sound small, epidemiological and infrastructure studies show that even small temperature increments on very hot days can substantially increase health risks, strain energy systems, and worsen wildfires and drought impacts.
Wider Implications
Europe is warming at more than twice the global average rate, and global temperatures are on track to exceed the Paris target of 1.5°C above preindustrial levels—optimistic scenarios project a peak near 1.8°C under current policies. Co-author Noah Diffenbaugh emphasizes that some additional intensification of extremes is already "committed" because of emissions already in the atmosphere, even if future emissions are sharply reduced.
The authors describe their approach as an advance in attribution science: it allows researchers to quantify how specific subsets of historical emissions have altered the probability and intensity of individual extreme weather events.
Takeaway
The study provides robust evidence that emissions since 2015 have already made recent European heat waves hotter and more damaging. The findings highlight the urgency of rapid emissions reductions combined with strengthened adaptation to protect vulnerable populations and infrastructure.
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