October 2025 New South Wales wildfires likely fueled by both human-driven climate change and natural variability

Contact Authors

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

Citation

• Faranda, D. (2025). October 2025 New South Wales wildfires likely fueled by both human-driven climate change and natural variability. ClimaMeter, Institut Pierre Simon Laplace, CNRS. https://doi.org/10.5281/zenodo.17454580

Press Summary

• Meteorological conditions leading to the October 2025 wildfires in New South Wales were significantly warmer, drier, and windier than they would have been in the past. Present-day conditions are up to 1.5 °C hotter and up to 2.5 km/h windier (up to 10 %) compared to similar past events.

• This event is associated with rare meteorological conditions. 

• Natural variability alone does not explain the exceptional conditions that fueled the October 2025 New South Wales wildfires.

Event Description

Large-scale wildfires broke out in New South Wales on 22 October 2025, affecting areas around Sydney during an intense early-season heatwave. Temperatures soared above 37 °C, prompting catastrophic fire danger warnings. According to the NSW Rural Fire Service, several major blazes threatened residential areas, forced evacuations, and damaged property on the city’s urban fringes. The fires were fueled by very low humidity, parched vegetation following a prolonged dry spell, and strong northwesterly winds exceeding 50 km/h, which made firefighting extremely difficult. Authorities issued total fire bans across large areas of the state.

The meteorological conditions were characterized by a pattern of surface-pressure anomalies with positive anomalies over inland New South Wales and negative anomalies offshore over the Tasman Sea, producing a strong inland–coastal pressure gradient toward the coast. Temperature anomalies were strongly positive, locally around +6–8 °C in the Sydney basin. Precipitation during the event was near zero across the affected area, while windspeeds were elevated (mostly 30–40 km/h, with pockets above 40 km/h), creating favorable conditions for ignition and rapid spread.

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). Extreme weather conditions, such as heatwaves, droughts, and strong winds 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 (including Australia) and lengthened fire weather seasons. In Australia, repeated analyses have shown a lengthening and intensification of fire seasons and a rising likelihood of catastrophic fire weather, particularly in New South Wales and Victoria (Di Virgilio et al. 2020)

Our analysis approach rests on looking for weather situations similar to those of the event of interest having been observed in the past. For this event, we have medium-low confidence in the robustness of our approach given the available climate data, as the event is exceptional in the data record.

ClimaMeter Analysis 

We analyze here (see Methodology for more details) how events similar to the meteorological conditions leading to the October 2025 wildfires in New South Wales 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°E–154°E, 30°S–40°S].

Surface pressure changes show no significant changes. Temperature changes show increases of up to +1.5 °C in the Sydney basin and surrounding areas.Precipitation changes reveal a general wetting trend, with present-day conditions up to 3 mm/day wetter across large parts of eastern New South Wales. However, these wetter areas are located far from the regions where the fires are concentrated. Wind speed changes indicate increased windiness, with winds up to 2.5 km/h stronger, particularly along the coastal and peri-urban areas near Sydney.

Similar past events show a seasonal shift, with events in the recent period occurring more frequently in October, compared to the past when they were more typical in late spring (November). Changes in urban areas reveal that Sydney experienced significantly warmer and drier conditions during this event compared to similar past conditions. Melbourne and Wollongong also experienced warmer temperatures, but the largest temperature and wind increases were detected in Sydney. These results suggest that meteorological conditions similar to those of the October 2025 Sydney wildfires are becoming more intense, in line with what would be expected under continued global warming. 

Finally, we find that sources of natural climate variability, notably the El Nino—Southern Oscillation and the Atlantic Multidecadal Oscillation, may have influenced the event. This suggests that the changes we see in the event compared to the past may be partly due to human driven climate change, with a contribution from natural variability. 

Conclusion

Based on the above, we conclude that meteorological conditions leading to the October 2025 New South Wales wildfires are up to 1.5 °C hotter and up to 2.5 km/h windier (up to 10 %) compared to similar past events.compared to similar past events. We interpret this as an event driven by rare meteorological conditions for which natural climate variability played a role.