new attribution study » Yale Climate Connections

Human-caused climate change worsened the ferocious January 2025 Los Angeles wildfires by reducing rainfall, drying out vegetation, and increasing the overlap between fire season and the winter Santa Ana wind season, according to a rapid analysis released today by World Weather Attribution, conducted by 32 researchers, including leading wildfire scientists from the U.S. and Europe. The fires burned over 50,000 acres, killed at least 28 people, and destroyed over 16,000 structures, according to Cal Fire. The study’s main findings:

• The hot, dry and windy conditions that drove the fires were about 35% more likely and 6% more intense due to 1.3 degrees Celsius of global warming that has occurred since preindustrial times, caused primarily by the burning of oil, gas and coal.
• These fire-prone conditions can be expected to recur about once every 17 years in the current climate, but will become a further 35% more likely if warming reaches 2.6 degrees Celsius by 2100, which is predicted to happen under three of the five main IPCC emission scenarios (from moderate to high-end).
• Low rainfall from October through December in the current climate is about 2.4 times more likely compared to the preindustrial climate, but this change cannot be confidently attributed to human-caused climate change.
• Fire-prone conditions because of human-caused climate change have increased by about 23 extra days each year, increasing the chance a fire will start from October through December, which coincides with the onset of peak Santa Ana wind season.
• Water infrastructure, not designed to fight a rapidly expanding wildfire, was unable to keep up with scale and extreme needs during the Eaton and Palisades wildfires.

The results echo the conclusions of an earlier UCLA rapid attribution study, which found, “Climate change may be linked to roughly a quarter of the extreme fuel moisture deficit when the fires began. The fires would still have been extreme without climate change, but probably somewhat smaller and less intense.”

Trumpeter Jens Lindemann performs “Smile” by Nat King Cole on the remains of his home in the Pacific Palisades after seeing it for the first time since evacuating. “Smile though your heart is aching” Music heals. #PalisadesFire @KTLA @ABC7 @GMA @NBCLA @latimes @FOXLA @USATODAY pic.twitter.com/7hogqs1Z7u

— Ryan Svendsen (@MusicBefore) January 22, 2025

How the stage was set for the wildfires

The rainy season in California usually begins between October and December, and typically marks the end of the wildfire season, nullifying the ability of the powerful wintertime Santa Ana winds to easily spread large and intense fires. However, Los Angeles County received its lowest May-December precipitation on record in 2024 (0.31 inches, 4.6 inches below average), accompanied by its fifth-hottest May-December temperatures on record, meaning that grasses and brush were dry and highly flammable when the fires broke out. (A primary way in which climate change worsens wildfire is through a strong, warming-driven increase of the atmosphere’s “thirstiness” or vapor pressure deficit, which exerts a drying effect on vegetation.) Additionally, above-average precipitation in the winters of 2022/23 and 2023/24, plus the record rains from Hurricane Hilary in the summer of 2023, had previously encouraged vegetation growth, providing more fuel for the fires (wildfires in this ecosystem are often limited by the amount of fuel they have).

To evaluate how wildfire risk is changing, the study looked at four measures: a drought index (using measured rainfall from October through December), the Fire Weather Index (FWI), which uses meteorological information (temperature, humidity, wind speed, and precipitation over the preceding weeks and days), the timing of the end of the dry season, and how circulation pattern that create the Santa Ana winds are changing. Their findings:

• The observed drop in precipitation (i.e., meteorological drought) was about a 1-in-20-year event in the current climate but would have been a 1-in-49-year event in the preindustrial climate (2.4 times less likely). However, climate models do not agree on the direction of precipitation trends in this region, and “we are unable to formally attribute this change to global warming,” the researchers concluded.
     
• Looking beyond precipitation alone, eight of the eleven models examined showed an increase in extreme January values of the Fire Weather Index (FWI) in Southern California, “increasing our confidence that climate change is driving this trend”, the authors wrote. They added, “Combining models and observations, we find that human-induced warming from burning fossil fuels made the peak January FWI more intense, with an estimated 6% increase in intensity, and 35% more probable.”
• Analyzing observations, the study found that “the length of the dry season has increased by about 23 days since the [period when] global climate was 1.3°C cooler. This means that, due to the burning of fossil fuels, the dry season, when a lot of fuel is available, and the Santa Ana winds, that are crucial for the initial spread of wildfires, are increasingly overlapping.” They attributed this increase in the dry season length to human-caused global warming.  
• Analyzing observations, the authors found that “the frequency of an atmospheric circulation pattern such as that of January 8, 2025, which is known to strengthen Santa Ana wind events, has increased in winter, raising the risk of weather conditions that drive the spread of wildfire. Whether this trend is attributable to human-caused climate change requires a more in-depth study of the patterns in observations and climate models.” For the future, climate models predict that global warming may promote a slight reduction in the frequency of early season (mainly Sep.-Nov.) Santa Ana winds because of a decreasing cool-season temperature differential between the ocean and continental interior, but this has not yet been observed. Little change in the magnitude of the strongest Santa Ana wind events is anticipated from future climate change.

The study did not look at how the enhanced vegetation and fuel loads caused by the extra precipitation that fell during the 2022-2023 and 2023-2024 wet seasons may have been influenced by climate change. However, the UCLA attribution study found that a small part (~10%) of this excess precipitation could be attributed to climate change. They wrote: “This effect may be associated with climate “whiplash”, a phenomenon where climate change is simultaneously projected to intensify precipitation totals in wet years, but also to intensify drought in dry years (Swain et al. 2018, Swain et al. 2025)”.

Costliest wildfire in world history

There is little doubt that the two January 2025 Los Angeles wildfires, the Palisades Fire and the Eaton Fire, will collectively be the costliest wildfire event in world history, even after adjusting previous events for inflation. A Jan. 23 analysis of insured damage estimates of the fires from insurance brokers Gallagher Re, Moody’s RMS, CoreLogic, Karen Clark & Company, and Verisk averaged $31 billion. Total damages will be much higher; Goldman Sachs estimated that total damages could be $10 billion higher, and one expert I heard from told me, “the direct overall economic cost will be as much as double the insured loss, but we won’t have clarity on that for a while. This is a rather complex situation on the insurance side.” (Note that damage estimates from weather company AccuWeather, of up to $250 billion, are not included, since their disaster damage estimates are typically wildly inflated from industry standard practices.)

According to Verisk, insured losses for the Palisades fire will be $20-25 billion, and will be $8-10 billion for the Eaton fire. Using inflation-adjusted damage estimates from EM-DAT, the international disaster database, the 2025 Palisades Fire alone would be the costliest fire in world history (Fig. 3). The previous record was held by the catastrophic Camp Fire of 2018, which killed 85 people in Paradise, Calif., and cost $20 billion. The 2025 Eaton Fire would likely rank as the sixth-costliest fire in world history.

By number of structures destroyed, the Palisades and Eaton wildfires are the second and third most destructive wildfires in California, trailing only the Camp Fire of 2018.

This remarkable remote camera footage from the peak of the #EatonFire as it roared through Altadena amid winds gusting 70-90 mph illustrates just what this was: a true firestorm, a literal blizzard of embers. The reality on the ground really *was* that extreme. #CAfire #CAwx https://t.co/oLjkC9oS81

— Dr. Daniel Swain (@Weather_West) January 17, 2025

Welcome rains fall in Los Angeles, but bring mudslides

The first significant precipitation since May fell in Southern California on Sunday and Monday, bringing widespread rains of 0.5-1.5 inches to fire-ravaged areas and snow to the higher peaks. In Los Angeles, 0.61 inches of rain fell on Sunday – more precipitation than fell in the previous eight months combined. These welcome rains should significantly reduce the fire danger in the coming weeks. Thanks in part to the rains, the Palisades and Eaton wildfires are now both more than 95% contained.