It’s Not Just the Heat

By Dave Levitan | May 2, 2025 | 1:55pm

Photo by Johannes Plenio/Unsplash

Climate Heat Waves

As the climate warms, the risk of “compound events” where one disaster follows closely on the heels of another is increasing. Two new studies put some numbers on specific examples of this, where extreme heat occurring in tandem with drought and wildfire smoke are raising the risks of health, agricultural, and other impacts. As always, just focusing on average temperature increases doesn’t paint the complete picture.

First, a study published on Friday in Science Advances looked at the “trans-Eurasian heatwave-drought train,” which sounds far more fun than it is. They found that a combination of warming sea surface temperatures in the northwestern Atlantic Ocean along with “enhanced” precipitation in the Sahel region in Africa are helping drive an increase in combination events. They examined tree ring data dating back three centuries, and while there has been plenty of natural variation in that period the results were clear: there has been a “radical shift” in the heatwave-drought combination in Europe and Asia. In fact, four of the top five such events in the record came after 2010, and the overall picture is of a trend “transcending natural variability.”

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“The consequences of this shift are profound, with significant implications for wildfires, agriculture, food security, water resources, and ecosystems,” wrote the study authors from South Korea, Thailand, Japan, and Sweden. “Given that future simulations predict continued intensification of these changes, urgent mitigation efforts are needed to address the escalating risks.”

Here in the US, the combo is between heat and things catching on fire. Again in Science Advances, authors from Ohio State and elsewhere used census tract-level data to examine trends in exposure to extreme heat, wildfire burn zones, and wildfire smoke between 2006 and 2020 in 11 western states. Again and unsurprisingly, some of these things are coinciding more than they used to.

The period from 2016 through 2020 saw significantly more co-exposure to extreme heat and wildfire smoke compared with both 2011-2015 and 2006-2010. There were regional and state differences here, with increasing heat exposure specifically in California, Colorado, and Nevada while smoke exposure increased most in Arizona, Colorado, Oregon, and Washington. California and New Mexico saw statistically significant increases in the co-exposure days for heat and smoke. Native American populations were disproportionately exposed to all of the hazards.

“Our research findings have public health implications,” the authors wrote, pointing out the body of literature that suggests synergistic negative effects on health from extreme heat and smoke inhalation. Both studies demonstrate a core challenge in preparing for a warmer world, where even the best predictions of a given sort of hazard need to then take the next step and consider what might happen alongside it.