Bushfires: Human factors ‘are having an impact on wildfires’

Human-induced climate change is promoting conditions on which wildfires depend, increasing their likelihood.

A human fingerprint was harder to detect in bushfires in Australia than elsewhere because of natural factors, a review of the most recent scientific literature published by Britain’s Met Office says.

A rapid response review of 57 peer-reviewed papers published since the Intergovernmental Panel on Climate Change ’s Fifth Assessment Report in 2013 was undertaken in response to Australia’s bushfires. The headline finding was human-induced climate change promoted conditions on which wildfires depended, increasing their likelihood.

For Australia, the review found “the divergence between anthropogenic and natural forcing ­signals is weaker, and more challenging to diagnose, than in other regions due to strong ­regional and inter-annual variability”.

These included El Nino and weather patterns in the Indian Ocean and over Antarctica.

“Impacts of anthropogenic climate change on fire weather extremes and fire season length are projected to emerge above natural variability (in Australia) in the 2040s,” it said.

The Met Office said the findings were consistent with the “Fire and Climate Change” summary of the 2019 IPCC Special Report on Climate Change and Land.

That summary found climate change was playing an increasing role in determining wildfire ­regimes alongside human activity, with future climate variability expected to enhance the rise and ­severity of wildfires in biomes such as tropical rainforests.

It said fire weather seasons had lengthened globally ​between 1979 and 2013 but global land area burned had declined in recent ­decades.

According to the Met Office rapid review, all the studies showed links between climate change and increased frequency or severity of fire weather — ­periods with a high fire risk because of a combination of high temperatures, low humidity, low rainfall and often high winds.

By 2019, models suggest that the impact of anthropogenic climate change on fire weather was detectable outside the range of natural variability in 22 per cent of global burnable land area.

The areas included Amazonia, southern Europe, Scandinavia and the western US and Canada.

Australia was less clear-cut because of strong regional and inter-annual variability in the effect of the El Nino-Southern Oscillation on fire weather.

“Other important regional weather patterns, such as the Indian Ocean Dipole and the Southern Annular Mode also contribute to natural variability in fire weather, but their effects are increasingly superimposed on more favourable background fire weather con­ditions”, the rapid review said.

“Impacts of anthropogenic climate change on fire weather extremes and fire season length are projected to emerge above natural variability in the 2040s.”

The rapid review said “fire weather only translates to fire ­activity and burned area if natural or human ignitions occur, and hence the sensitivity of burned area to changes in fire weather ­varies ­regionally. Correlation between fire weather and burned area is strongest in the boreal and tropical forests, where fire weather is the main limitation to fire.

“On the other hand, burned area is insensitive to fire weather in regions where fuel stocks or human suppression are the key fire limitations.”

The review said humans could affect wildfire occurrence by managing fuel loads and suppressing ignitions during fire weather.

“Globally, humans have reduced the global extent of burned area in recent decades and probably the last century”, the review said. “Nonetheless, direct human effects on burned area show significant regionality. While the conversion of savannas to agricultural land has been the principal driver of the reduced global burned area in recent decades, burned area has increased in closed-canopy forests and is associated with rising population, cropland and livestock density.”

The review was conducted by scientists from the University of East Anglia, Met Office Hadley Centre, University of Exeter, Imperial College London, and CSIRO Oceans and Atmosphere.