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New research finds that not only will climate change make heat waves hotter and longer, but the lengthening of heat waves will accelerate with each additional fraction of a degree of warming.

In published in the journal Nature Geoscience, researchers led by UCLA and the Universidad Adolfo Ibañez in Santiago, Chile, found that the longest heat waves will see the greatest acceleration, and the frequency of the most extreme heat waves will increase the most. The duration of a heat wave exacerbates the risk to people, animals, agriculture and ecosystems.

By incorporating variables into climate models that account for how each day's temperature influences the temperature of the following day, the researchers detected this acceleration at a global level. The equation they developed has the flexibility to analyze one region or to gain additional broad insight by analyzing multiple regions as a whole, said senior author and UCLA climate scientist David Neelin.

"Each fraction of a degree of warming will have more impact than the last," said Neelin, a distinguished professor of atmospheric and oceanic sciences who studies climate variability. "The acceleration means that if the rate of warming stays the same, the rate of our adaptation has to happen quicker and quicker, especially for the most extreme heat waves, which are changing the fastest."

People have already begun feeling longer heat waves in recent decades, Neelin noted. Just this month, a late-June heat dome settled over much of the U.S., breaking daily heat records, damaging a Virginia drawbridge and causing heat illness among dozens at a high school graduation. Europe sweltered through the first week of July as heat closed the Eiffel Tower and Wimbledon launched "Operation Ice Towel" for its record hottest opening day.

"We found that the longest and rarest heat waves in each region—those lasting for weeks—are the ones that show the greatest increases in frequency," said lead author Cristian Martinez-Villalobos, an assistant professor of engineering and science at the Universidad Adolfo Ibáñez with expertise in theoretical modeling. "By taking into account the natural variation of temperatures at each location, we find that recent observed trends of heat wave durations already follow a similar pattern of acceleration predicted by climate models."

Seasons and places that currently have less variability in their weather will see the biggest changes, Neelin said.

"If you have large variations in current climate, then a fraction of a degree change will have less impact than if you have a more stable climate," Neelin said. "So impacts in tropical regions tend to be bigger than in temperate regions, and winter warm spells will change less than summer because summer tends to have smaller variability."

Southeast Asia and the equatorial regions of South America and Africa will likely see some of the greatest impacts. The research projected that heat waves in equatorial Africa lasting more than 35 days would happen a whopping 60 times more often in the near future (2020 to 2044) compared with the recent past (1990 to 2014).

This research's contribution of a formula that can describe climate change impacts across regions is a valuable tool, Neelin said. Future research will need to evaluate how the longer heat waves will affect variables like soil moisture and wildfire risk, which in turn will help inform critical adaptations for agricultural planning, utility sector strategies and urban planning from cooling centers to shade plantings.

"Addressing those will depend on having high-accuracy weather and climate models, but the current federal budget is putting a pause on the United States' capabilities and eliminating excellent young scientists from the field," Neelin said. "Deprioritizing and defunding climate and science research will limit our capacity to make region-specific projections for risk management. Without that, we'll have much less ability to adapt to climate change at the very time when we need to accelerate adaptation planning."