Climate change made the combination of high heat, dry climate, and forceful winds that drove this month’s devastating Los Angeles wildfires about 35% more likely, according to a report published today by World Weather Attribution (WWA).
The study, conducted by nearly three dozen researchers at institutions in the United States and Europe, examined the Fire Weather Index, which incorporates meteorological factors such as temperature, relative humidity, wind speed, and precipitation to estimate fire danger. Researchers compared the index and resulting likelihood and intensity of fires in a 2025 climate to how they might have been under preindustrial conditions, in which the global mean surface temperature was approximately 1.3°C cooler.
The factors that led to the Los Angeles fires are expected to coincide, on average, every 17 years, whereas in preindustrial conditions they may have occurred together only every 23 years.
The Palisades and Eaton Fires in Los Angeles County have burned nearly 40,000 acres (160 square kilometers), claiming at least 29 human lives and more than 14,000 structures. What ignited the first flames of these fires is not yet known, but they were fanned by what Chad Thackeray called “a recipe for disaster.” Thackeray is a climate scientist at the University of California, Los Angeles (UCLA), who was not involved in the new study.
Water years 2022–2024 brought Los Angeles to a 2-year rain total not seen since the highs of 1888–1890, leading to a buildup of vegetation. Then, a record-breaking heat wave in summer 2024 dried that vegetation out, and Southern California’s rainy season, usually experienced between November and March, were unusually delayed. Between 1 May 2024 and 25 January 2025, the region experienced just 0.3 inch (0.8 centimeter) of rain. Thackeray said the total is normally closer to 6 inches (15 centimeters). Then came dry Santa Ana winds, which flow toward the coast in the region between October and March.
“The impact of these fires and the timing of these fires in the core of what should be the wet season differentiate this event as an extreme outlier.”
“While Southern California is no stranger to high impact wildfires, the impact of these fires and the timing of these fires in the core of what should be the wet season differentiate this event as an extreme outlier,” said John Abatzoglou, a climatologist at the University of California, Merced, in a statement. “This was a perfect storm of climate-enabled and weather-driven fires impacting the built environment.”
The Role of Climate Change
According to the report, California’s dry season has grown about 23 days longer since the preindustrial era, when global climate was 1.3°C cooler. This increase, the researchers said, is attributable to climate change, but their study did not quantify exactly to what degree. A longer dry season means there is increasing potential for overlap between the dry season, when there is lots of brush to burn, and the peak of the Santa Ana winds, which can speed the spread of fires once they ignite.
Southern California has the most volatile hydroclimate in the United States, usually experiencing either extremely high or extremely low amounts of precipitation, said Sasha Gershunov, a research meteorologist at the University of California, San Diego’s Scripps Institution of Oceanography who was not involved in the study. Previous research has shown that “climate whiplash,” or transitions between the two extremes, has also grown more common in a warming climate.
“Very wet years with lush vegetation growth are increasingly likely to be followed by drought, so dry fuel for wildfires can become more abundant as the climate warms,” said Theo Keeping, a climate and environmental scientist at the Leverhulme Centre for Wildfires, Imperial College London, in a statement.
However, Gershunov added, the rainy season has never arrived so late in the 150 years’ worth of records that exist for the region.
“I can’t say that this winter precipitation is so late because of climate change, but I can say that it’s consistent with what we expect for a warmer future,” he said. “And even in a warmer future, this would still be extreme as far as how late the precipitation is.”
The past weekend brought about 0.5 to 1.5 inches (1.3 to 3.8 centimeters) of rain across the Los Angeles Basin, more than the area has cumulatively received since May 2024. “It’s a start,” Abatzoglou said at a press conference. “Whether it’s going to really end the fire season, I don’t know. I think, temporarily, it’ll pause it.”
The researchers’ observational analysis showed that low rainfall from October to December is about 2.4 times more likely now than it was in the preindustrial climate. As with the extended length of the dry season, the researchers attribute this general shift to climate change but did not determine the quantitative impact of climate change on low rainfall in this study.
What’s Next?
The study projected that if the world warms by another 1.3°C by 2100, fire-prone conditions will grow another 35% more likely.
“Without a faster transition away from planet-heating fossil fuels, California will continue to get hotter, drier, and more flammable.”
The authors noted that there is a high level of uncertainty in their reported numbers, which have not yet been peer reviewed, in part because Southern California has an inherently volatile hydroclimate. But their collective analysis in the form of observational results and climate modeling all points to the same conclusion: The conditions most conducive to fire activity are growing more common as the climate warms and will continue to do so under further warming.
The findings align with a report issued by a team of UCLA researchers, including Thackeray and two of the researchers on the WWA study, on 13 January that suggested that the fires were made larger and more intense by climate change because climate change made the vegetation in the region 25% drier than it otherwise would have been.
“Without a faster transition away from planet-heating fossil fuels, California will continue to
get hotter, drier, and more flammable,” said Clair Barnes, a statistician at Imperial College London and WWA researcher, in a statement.
—Emily Dieckman (@emfurd), Science Writer