- Share via
An extremely warm summer and fall. An unusually dry winter. Hillsides covered with bone-dry vegetation. And strong Santa Ana winds.
In the mix of conditions that have contributed to the most destructive fires in L.A. history, scientists say one significant ingredient is human-caused climate change.
A group of UCLA climate scientists said in an analysis this week that if you break down the reasons behind the extreme dryness of vegetation in Southern California when the fires started, global warming likely contributed roughly one-fourth of the dryness, one of the factors that fueled the fires’ explosive spread. Extreme heat in the summer and fall desiccated shrubs and grasses on hillsides, they said, enabling those fuels to burn more intensely once ignited.
The scientists said without the higher temperatures climate change is bringing, the fires still would have been extreme, but they would have been “somewhat smaller and less intense.”
Coverage of the Eaton and Palisades fires, including stories about the unprecedented losses, issues firefighters faced and the winds.
The conditions that made such catastrophic fires possible are like three switches that all happened to be flipped on at the same time, said Park Williams, a climate scientist who prepared the analysis with colleagues Alex Hall, Gavin Madakumbura and others in UCLA’s Climate and Wildfire Research Initiative.
“Those switches are very high fuel loads, extraordinarily dry fuels and an extraordinarily strong Santa Ana wind event,” Williams said. “All of which are mostly due to natural bad luck.”
But because all those natural switches lined up, he said, “now the fact that the atmosphere is warmer because of climate change, then the fuels are drier than they would have been otherwise, and therefore the fires are more intense and larger than they would have been otherwise.”
The scientists said more detailed peer-reviewed studies that examine the influences of climate change and natural factors will take time, and that they prepared their analysis as a starting point for deeper research.
Williams and his colleagues examined the last two wet winters, which nourished growth of chaparral and grasses across Southern California. They noted that research has projected more extreme atmospheric river storms because of global warming, but that thus far this trend has not emerged in the data in the western U.S., making any influence of climate change in the last two wet years “highly uncertain.”
They analyzed the extraordinarily dry conditions in Southern California, where no significant rain has fallen in eight months. A weather station in Los Angeles recorded just 0.29 of an inch of rain from May 1 through Jan. 8, ranking the second driest since 1877, behind 1962-63, when there was 0.15 of an inch. However, the researchers said the degree to which climate change may have promoted the unusually long dry spell remains “highly uncertain.”
The exceptionally hot summer and fall of 2024, however, are part of a clear trend toward warmer temperatures attributed to human-caused climate change, the scientists said.
The summer-fall period ranked as the region’s third hottest since 1895, and it occurred during a year that U.S. government agencies confirmed was Earth’s warmest since the start of recordkeeping in 1880.
The researchers said the heat in Southern California appears to have been partly responsible for a dramatic decline in dead vegetation “fuel moisture,” which by January was among the driest on record, and that these conditions were “extremely favorable for wildfire.”
They estimated that the abnormal heat accounted for approximately 25% of the dryness of vegetation, while the lack of rain accounted for the other 75%.
When the strong Santa Ana winds arrived on Jan. 7, as sometimes happens this time of year, they brought the final piece in the mix of factors that set the stage for high fire danger.
“The clearest way climate change is affecting fire in the western United States and California is through the direct influence that warmer atmospheric temperatures have,” Williams said, pointing to his own previous research and other studies. “A warmer atmosphere is a thirstier atmosphere, and so all else equal, fuels will dry out more quickly in a warmer world.”
Firefighters in Pacific Palisades and Altadena have repeatedly been hampered by low water pressure and dry hydrants, revealing limitations in local water systems designed to supply neighborhoods.
Other scientific studies have found that human-caused warming is driving more severe droughts and contributing to larger and more intense wildfires in the Western U.S.
However, Williams said, there are important differences between regions where fires erupt in forests with abundant vegetation fuel and regions like Southern California, where fires often burn through sparser shrubs and grasses.
California as a whole has seen a trend toward larger wildfires in recent years. But in coastal Southern California, the data show there hasn’t been a trend toward larger fires over the last four decades, and there actually has been a decrease in the number of fires over this period — possibly because people have become more careful about accidental ignitions or because a shift toward drier average conditions has made vegetation sparser in many years, Williams said.
“What you see is that most years have hardly any fire, and then some years have a lot of fire,” Williams said. “Every once in a while, Southern California gets unlucky, and those three switches get flipped on at once.”
Some studies have projected that drier ecosystems in the West, like much of Southern California, will probably see less fire on average in a hotter, drier future because more aridity brings reductions in the amount of flammable vegetation. However, Southern California is still likely to episodically get wet years that bring more vegetation growth. And as these fires have shown, Williams said, “the wetter the prior year, the more fire should be expected the next year.”
“In those rare years when all the pieces come together to promote wildfires, the fact that the atmosphere is warming due to human-caused climate change is likely to make many fuels even drier than they would have been otherwise,” Park said. “This will allow fires in these episodic years to grow larger and more intense than they would have under cooler conditions.”
The causes that sparked the fires are under investigation, and the scientists noted that because there are no natural ignition sources this time of year, the fires were almost certainly started by human activity in some way — whether sparks from a power line, fireworks, arson or some other cause.
The UCLA team prepared the analysis during tense days while they watched the losses unfold and heard from friends and colleagues who were evacuating or whose homes burned.
This week, the professors have been teaching classes online under a university decision as wildfire smoke has led to poor air quality on campus.
“This is fundamentally a natural disaster. Once you have the ignitions, we do live in a place that has really extreme events,” said Hall, another climate scientist who prepared the analysis.
“Climate change is kind of juicing this a little bit. We can’t fully quantify it, but it’s something,” Hall said. “We know that that warmth dried out the vegetation. And we know that a certain fraction of the moisture deficit that we had when the fires started can be attributed to that unusual warmth.”
Research shows rapid shifts between wet and dry extremes are increasing. Scientists say this ‘hydroclimate whiplash’ contributed to California’s devastating fires.
Without the influence of climate change, he said, “it probably would have been somewhat smaller and probably easier to fight.”
More deeply examining the influence of global warming will involve studies that delve further into the complex dynamics of the fires, weather conditions and rising temperatures, Hall said.
These and other attribution studies are taking on growing importance as California, Hawaii and other states sue oil companies, seeking billions of dollars in damages for effects linked to the burning of fossil fuels.
Warmer summer temperatures and the drying of vegetation are trends that have been observed in recent decades associated with human-caused warming, said Julie Kalansky, a climate scientist and deputy director of the Center for Western Weather and Water Extremes at UC San Diego’s Scripps Institution of Oceanography.
She pointed to research showing that higher temperatures have brought increased “evaporative demand” in recent decades, pulling more moisture from the landscape in the Western U.S., a finding that the authors said points to a need to plan for increased wildfire risks.
As for the L.A. fires, Kalansky said additional studies will be needed to gain a better understanding of the contribution of climate change and “to be able to put some more definitive numbers on that.”
The UCLA campus in Westwood is not in an evacuation zone but right next to mandatory evacuation areas as well as evacuation warning zones. But many on- and off-campus students have already left.
The UCLA scientists wrote that because climate change is set to continue, so will the “expectation of even more intense wildfires when all of the other necessary conditions for fire occur.”
They called for focusing wildfire mitigation efforts “around factors we can control, and the damages we can prevent,” such as preventing ignitions during fire weather, adopting strategies to prevent homes from burning so easily, and planning development in zones with lower fire risk.
Scientists can also play an important role in identifying fire-prone areas that should be avoided because of their location or exposure to combustible vegetation, Williams said.
“In the long term, the knowledge that these types of extreme events do happen here, when all of the factors align, should hopefully guide decisions about where to rebuild,” he said. “Some places, when the fuels come back, the fire danger will be very high again.”
