Greenhouse Gases Emitted Since 2015 Intensifying Europe's Heat Waves, Study Finds
Emissions from the past decade have measurably increased the intensity of recent heat waves in Europe, according to new research.
Greenhouse gas emissions released since the 2015 Paris Climate Agreement have measurably intensified recent heat waves in Europe, according to a study published in Geophysical Research Letters. Lead author Jared Trok, a PhD student at the Stanford Doerr School of Sustainability, stated that these emissions have "substantially and significantly increased the intensity of Europe's recent individual heat waves," a finding that held true for the continent's hottest week in every year since at least 2021.
The study’s findings emerge as Europe experiences back-to-back heat waves that have broken temperature records and contributed to at least 35,000 excess deaths. The Paris Agreement, adopted by nearly 200 countries in 2015, aimed to limit global warming to 1.5°C above pre-industrial temperatures. However, current projections indicate the world is on track to surpass this target, with optimistic estimates predicting a peak warming of 1.8°C under existing climate policies.
Even fractions of a degree above the 1.5°C threshold carry significant consequences, including intensified extreme weather, ecosystem loss, and widespread impacts on human health and food security. Europe is particularly vulnerable, warming at more than twice the global average rate. Record-breaking heat waves occurred across the continent in June and July of 2025, only to be surpassed by those in 2026. Surface air temperatures exceeded 40°C (104°F) in several countries, reaching up to 46°C (114.8°F) in Spain and Portugal.
To reach their conclusions, the researchers utilized a generative artificial intelligence model, specifically a diffusion model trained on simulated weather data from 10 global climate models. This model was used to predict how extreme heat waves in Europe might have developed under varying global emissions levels. "This is a purpose-built machine learning model that we trained on large amounts of climate model data…to make predictions about how individual heat waves might have unfolded differently if those same weather patterns had occurred under different levels of human emissions," Trok explained.
The team input observed weather conditions from Europe’s most intense annual heat waves between 2016 and 2025 into the model. These conditions typically involved a persistent high-pressure system known as a heat dome. The model then simulated daily temperatures under the emission levels present during each extreme heat event, as well as under the lower emissions levels of 2015. The research indicated that emissions from the past decade increased the intensity of 2025 heat waves by approximately one-third of a degree Celsius.
"That third of a degree might seem very small, maybe imperceptible to us walking around, but there's a large body of scientific literature that suggests that even small increments of temperature on a hot day can have these disproportionate impacts on the damages caused by those heat waves," Trok noted.
Scientists have long understood the link between burning fossil fuels, greenhouse gas trapping, and rising global temperatures. Recent advancements in research methodologies have enabled the study of how historical emissions influence extreme weather events. The researchers describe their methodology as a significant advancement in climate modeling.
"This research shows that we can systematically and objectively ask questions about subsets of historical emissions, including individual heat waves," said co-author Noah Diffenbaugh, a professor at the Stanford Doerr School of Sustainability. "A key part of what we've identified here is we've been able to say with high confidence that this subset of emissions has shifted the distribution of temperatures that could occur during this individual heat wave to such an extent that we can say we are very confident that this individual heat wave would have been cooler if the same weather patterns had occurred without this subset of emissions."
Diffenbaugh also highlighted the study's implications as a warning, emphasizing that emissions already released will continue to affect the climate regardless of future mitigation efforts. "Even in the context of the most optimistic, ambitious future for reducing emissions, there's still more intensification of extremes that is essentially committed,” he stated.