They found that the emissions from the last decade increased the intensity of 2025 heat waves by roughly a 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,” says Trok.
Scientists have long known that the burning of fossil fuels trap greenhouse gases in the atmosphere, raising global temperatures. In recent decades, researchers have developed methods to study how historical emissions have affected heat waves, hurricanes, droughts, wildfires, and other extreme weather events. The researchers say that the methodology represents a step forward for climate modeling.
“This research shows that we can systematically and objectively ask questions about subsets of historical emissions, including individual heat waves,” says co-author Noah Diffenbaugh, 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.”
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