Study Ties Europe's Hotter Summers to Emissions Released Since the Paris Agreement

An open-access study published Sept. 22 in Geophysical Research Letters reports that greenhouse gases released since the 2015 UN Paris Agreement have already made Europe's summer heat extremes more intense.

The researchers describe the work as an answer to a limit in existing methods: those methods can say little about changes in extreme weather caused by small subsets of human emissions and less about any single event.

The study comes from Jared T. Trok of Stanford University's Doerr School of Sustainability, the senior author Noah S. Diffenbaugh of the same school and colleagues at Boston University and Colorado State University. They trained a machine-learning model to generate maps of daily surface temperature at different levels of cumulative emissions, the running total released to date. Each run is conditioned on the weather pattern the real event had, which is how the team holds the atmosphere fixed and varies only the emissions.

On that basis, the authors report what they call strong evidence, better than 95% probability, that emissions released since the Paris Agreement have increased the intensity of Europe's summer temperature extremes since 2021. For Europe's June 2025 heat wave, the model gives a greater than 99% probability that the temperature averaged across the region would have been lower, by a median of 0.34 °C, had the same large-scale weather occurred at 2015 levels of cumulative emissions. Both numbers come from comparing model runs, not from measurements.

The study lists the National Science Foundation as its funder.