January 2025 California wildfires have been fueled by meteorological conditions strengthened by human-driven climate change

Contact Authors

• Greta Cazzaniga, IPSL-CNRS, France 📨 greta.cazzaniga@lsce.ipsl.fr  🗣️ Italian, English, French

• Davide Faranda, IPSL-CNRS, France  📨  davide.faranda@lsce.ipsl.fr 🗣️French, Italian, English

Press Summary (First published 2025/01/10)

• Meteorological conditions similar to those triggering January 2025 California wildfires are up  5°C warmer, 3 mm/day (up to 15%) drier, and up to 5 km/h (up to 20%) windier in the present compared to the past, in the area interested by the fires. 

• This event was associated with very rare meteorological conditions 

• We ascribe the strengthened winds, higher temperature, and drier conditions triggering January 2025 California wildfires to human-driven climate change, and natural climate variability likely played a minor role.

Event Description

Beginning on January 7, 2025, multiple catastrophic wildfires, which are still ongoing, have impacted the Los Angeles metropolitan area and its surrounding regions. The fires were fueled by the interplay of different meteorological and hydrological conditions: very low humidity, dry conditions (with very little moisture over the past several months), and Santa Ana winds, exceeding 130-160 km/h in some places. The Santa Ana winds typically originate from cool and dry high-pressure masses in the Great Basin. The dry and powerful winds blow down the mountains towards the Pacific Coast, with gusts that can reach hurricane strength.

As of January 10, the wildfires have resulted in ten casualties, damaged thousands of structures, forced nearly 180,000 residents to evacuate, and burnt around 30,000 acres. The two largest fires were the Palisades Fire (in the Santa Monica Mountains) and the Eaton Fire (in the Altadena area of Los Angeles). Several celebrities, including Paris Hilton, Miles Teller, and Leighton Meester, lost their homes, while others like John Goodman and Anthony Hopkins were also deeply affected. The fires resulted in the cancellation of film premieres and award ceremonies, such as the Critics' Choice Awards, and disrupted community life. Relief initiatives, led by figures like Bethenny Frankel and Steve Guttenberg, are underway to support affected residents. Despite the tragedy, the community and public figures have rallied to navigate this unprecedented disaster, emphasizing resilience and solidarity.

The Surface Pressure Anomalies show a low-pressure area (cut-off low) over Southern California with values up to -10 hPa.  Temperature Anomalies display conditions up to +5°C warmer in the area affected by the fire. Precipitation data show dry conditions. Wind speed Data indicates strong winds blowing from California Mountain ranges to the Pacific Ocean. These winds are triggered by cut-off lows over California.  We remind you that our analysis is based on ERA5 data. This product does integrate some station observations, especially for rain data. The values reported here can be different from those observed at single weather stations.

Climate and Data Background for the Analysis

Wildfires are responsible for 70% of global biomass burning each year and they release vast amounts of atmospheric trace gases and aerosols (van der Werf et al., 2017). Extreme weather conditions, such as heatwaves, droughts, and heavy precipitation, contribute to the conditions that favor wildfires. Although fires are part of natural ecosystems, the IPCC AR6 WG1 highlights the growing influence of climate change on wildfire frequency and extension. Indeed, the effect of climate change on the frequency and intensity of climate extremes contributes, in turn, to the change in the frequency and intensity of wildfires.  The IPCC report reports with medium to high confidence that human-induced climate change has significantly increased areas burned by wildfires in certain regions and lengthened fire weather seasons. Furthermore, wildfires now affect regions previously unexposed to such risk (Jolly et al., 2015, Artés et al., 2019).  In the last years, fire seasons of unprecedented magnitude occurred in diverse regions such as California (Goss et al. 2020), the Mediterranean basin (Ruffault et al. 2020), and Brazilian Pantal (Ferreira Barbosa et al., 2022).   Williams et al., 2019 observed that, in California, the annual burned area increased fivefold during 1972-2018, mainly due to summer forest fires and that large fall fires are likely to become more frequent with global warming. Moreover, Goss et al. 2020 showed that in California the observed frequency of autumn days with extreme fire weather has more than doubled since the early 1980s. 

Our analysis approach rests on looking for weather situations similar to those of the event of interest having been observed in the past. For the January 2025 California wildfires, we have medium-high confidence in the robustness of our approach given the available climate data, as the event is similar to other past events in the data record.

ClimaMeter Analysis

We analyze here (see Methodology for more details) how events similar to the meteorological conditions leading to the January 2025 California wildfires have changed in the present (1987–2023) compared to what they would have looked like if they had occurred in the past (1950–1986) in the region [130°E 80°E 20°N 50°N]. The Surface Pressure Changes do not show any significant changes between the two periods. The Temperature Changes show that similar events produce temperatures in the present climate up to 5 °C warmer than what they would have been in the past. Precipitation Changes show that present events are dryer (up to 15%) than the past. Windspeed Changes indicate up to 5 km/h windier conditions over the areas interested by the fires. We also observe that Similar Past Events previously occurred mainly in January, while in the present climate, they are more frequent in February.  The analysis of the affected urban areas reveals that Los Angeles, San Francisco, and San Diego are up to 3 °C hotter in the present than in the past while we do not observe significant changes concerning windspeed and precipitation. 

Finally, we find that sources of natural climate variability did not influence the event. This means that the changes we see in the event compared to the past may be primarily due to human-driven climate change.

Conclusion

Based on the above, we conclude that meteorological conditions similar to those triggering January 2025 California wildfires are up  5°C warmer, 3 mm/day (up to 15%) drier, and up to 5 km/h (up to 20%) windier in the present compared to the past, in the area interested by the fires.  We interpret the January 2025 California wildfires as an event driven by very rare meteorological conditions whose characteristics can be ascribed to human-driven climate change.