May 2025 Canada wildfires have been fueled by meteorological conditions mostly strengthened by human-driven climate

Contact Authors

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

• Chen Lu, ICTP, Italy, 📨clu@ictp.it,🗣️English, Chinese

• Gabriele Messori, Uppsala University, 📨gabriele.messori@geo.uu.se  🗣️Swedish, French, Italian, English

• Valerio Lucarini, University of Leicester, 📨v.lucarini@leicester.ac.uk  🗣️English, French, German Italian

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

Citation

• Cazzaniga, G., Lu, C., Messori, G., Lucarini, V., & Faranda, D. (2025). May 2025 Canada wildfires have been fueled by meteorological conditions mostly strengthened by human-driven climate. ClimaMeter, Institut Pierre Simon Laplace, CNRS. https://doi.org/10.5281/zenodo.15719010

Press Summary

• Meteorological conditions similar to those causing wildfires in Canada are up to 3 °C (up to 15%) warmer and 2 km/h (10%) windier in the present than they have been in the past. 

• This event was associated with very rare meteorological conditions 

• We mostly ascribe the increase in temperature and wind in conjunction with the Canada wildfires to human driven climate change and natural climate variability likely played a modest role.

Event Description

Between 27 and 29 May  2025, a major wildfire outbreak occurred across Canada, particularly in Manitoba, Saskatchewan, Alberta, and British Columbia, marking one of the most intense early-season fire events on record. Several of the fires are still active at the time of writing. Manitoba, already severely affected by many wildfires in mid-Between 27 and 29 May  2025, a major wildfire outbreak occurred across Canada, particularly in Manitoba, Saskatchewan, Alberta, and British Columbia, marking one of the most intense early-season fire events on record. Several of the fires are still active at the time of writing. Manitoba, already severely affected by many wildfires in mid-May, emerged as one of the hardest-hit provinces. As of 20th May nearly 200,000 hectares of land were scorched and over 17,000 residents were forced to evacuate towns including Flin Flon, Lac du Bonnet, and Swan River (The Guardian). Two civilians died in Lac du Bonnet as fires overwhelmed parts of the northeast region.  By 29 May, the national area burned had exceeded 1.58 million hectares. The rapid spread of flames prompted provincial states of emergency in Manitoba on 28 May and in Saskatchewan on 29 May. The Canadian Interagency Forest Fire Centre elevated the national preparedness level to its maximum (Level 5), and international firefighting assistance was mobilized, including the deployment of U.S. air tankers and personnel starting on 31 May. The fires generated massive smoke plumes, severely affecting air quality across central and eastern Canada and spilling into U.S. states such as Minnesota, Wisconsin, Michigan, Illinois, and New York. Alerts were issued in many of these regions by late May. By early June, satellite and ground observations confirmed the smoke had drifted over 5,000 miles, reaching Europe. This follows similar patterns of extremely large scale smoke advection observed in 2023 and 2024.

The meteorological conditions were characterized by positive surface pressure anomalies of up to +8 hPa over the northern United States (south of the wildfire zone), and negative anomalies of up to –10 hPa across northern Canada (north of the wildfire zone). Temperatures were mostly higher than normal over the region, with anomalies reaching up to +12°C along the western coast of the Hudson Bay. Precipitation was absent over the whole region affected by wildfires. Winds up to 20 km/h were observed all over Canada, reaching 30 km/h on the east coast. The data used in this analysis come from the ERA5 reanalysis, which combines model output with available observational data, including ground stations and satellite measurements. Differences with localized station observations may occur.

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). Aerosols from forest fires are responsible for extreme levels of pollution (Rooney et al. 2018) Extreme weather conditions, such as heatwaves, droughts, and strong winds create 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 extent. Indeed, the effect of climate change on the frequency and intensity of climate extremes contributes, in turn, to modulating the frequency and intensity of wildfires, leading to a cycle of heat, drought, and fire (Sutanto et al. 2020, Libonati et al. 2022, Lucarini et al. 2023) The IPCC report states 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 recent years, fire seasons of unprecedented magnitude have 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).  

Wildfires are part of the natural cycle of the boreal forests of Canada. However, in a warming climate, wildfires in these regions have become more frequent, more intense and longer-lasting. The 2023 Canadian wildfire season broke by far the record of burnt area in the modern observational period, and 2024 ranked second. Some fires – so-called zombie fires – even survive the winter season, smoldering under the snow and regaining vigour during the successive warm season.

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 May 2025 Canada 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 May 2025 Canada 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 [145°W 155°W 28°S 36°S]. Surface pressure changes show no relevant differences between the two periods over western Canada, and an increase over parts of Ontario (up to +2 hPa). Temperature changes show increases of up to +3°C over the British Columbia Coast and up to +2°C inland, where most of the wildfires occurred. Wind changes display somewhat windier conditions over parts of the Canadian Prairies, particularly over Manitoba, with an increase of up to 2 km/h in the present-day conditions.

Similar past events show a weak seasonal shift, with an occurrence increase in May in the present period compensated by a decrease in occurrence in April. Changes in urban areas reveal that Edmonton and Regina experienced significantly warmer (almost +1.5 °C) and windier (almost +1.5 km/h) conditions during this event compared to similar past conditions, while Winnipeg experienced significantly windier conditions.

These results suggest that weather situations similar to those of the May 2025 Canada wildfires are leading to warmer and windier conditions , in line with what would be expected under global warming. Our results also suggest that sources of natural climate variability, such as the El Niño Southern Oscillation (ENSO), may have played only a secondary role in shaping the observed event.

Conclusion

Based on the above, we conclude that meteorological conditions leading to the May 2025 wildfires in Canada are up to 3 °C warmer and up to 2 km/h windier (up to 10%) compared to similar past events. We interpret this event as an event driven by very rare meteorological conditions, whose characteristics were mostly strengthened by human-driven climate change.