What fuelled Australia’s “Black Summer” fires?

Climate and bushfire experts have weighed in on links between human-generated climate change and last summer’s unprecedented, catastrophic bushfires that razed parts of Australia.

The paper, published in the Nature journal Communications Earth & Environment, highlights how climate variability and long-term trends combined to create the conditions that enabled the fires to burn out of control for months on end. 

These include hot, dry, windy weather often sparked by cold fronts, a build-up of prolonged, severe droughts, and forests comprised of fire-prone eucalyptus trees with accumulated expanses of vegetation, debris and dead wood. All that’s needed is a spark to ignite it – a risk factor compounded by dry lightning, which has increased over the past five decades.

Added to that, the team notes drops in rainfall during cool seasons in the south-eastern states, reaching a record low in 2019 compounded by an accumulated decline over the past 20 years. More broadly, they describe how factors such as greenhouse gas concentrations, ozone levels and atmospheric instability could fuse to increase fire risk.

They also draw on palaeoloclimate data that suggest fire-promoting conditions across the tropical Pacific and Indian oceans are more frequent than the natural variability evident in pre-industrial times.

Noting that previous predictions of increasing fires have proved true, the team warn it’s going to keep getting worse, and call for urgent actions to mitigate the risk. This comes on the heels of a statement for climate action signed by more than 400 scientists.

“[P]rojections made more than a decade ago that increases in climate-drive fire risk would be detectable by 2020, have indeed eventuated,” they write. 

The “extensive area of forest burnt, the radiative power of the fires, and the extraordinary number of fires that developed into extreme pyroconvective events [fire-generated thunderstorms] were all unmatched in the historical record.” 

Led by Australian National University climate professor Nerilie Abram, the scientists from across Australia and Europe say insights from the 2019–20 “Black Summer” offer critical insights for managing fires across the globe. 

In their review, which supports the NSW Bushfire Inquiry and the Australian Government’s Royal Commission, Abram and colleagues identify multiple ways in which climate change is increasing the fires’ severity, some well understood while others need more research.

“During the Black Summer fire disaster it became clear that there was an urgent need for a clear assessment of what we know – and what we don’t yet fully know – about how climate change will alter Australia’s fire risk in the future,” says Abram.

“Bushfire risk is complex and driven by many factors operating at multiple scales, but this study is a timely reminder of how critical climate and weather extremes are,” adds co-author Hamish Clarke, from the NSW Bushfire Risk Management Research Hub.

To address future events the team highlights recommendations from the government’s Royal Commission to reduce community and ecosystem vulnerability, limit exposure and enhance strategies to prevent or extinguish fires.

While acknowledging that other factors contribute to amplified fire risk, ultimately they underscore the importance of vigorous efforts to reduce human-caused global warming.

“When we look to the future we see southeast Australia could continue to become drier in winter and experience more frequent weather fronts in summer that cause dangerous fire weather,” says Abram.

“We saw during our Black Summer how severe bushfires in Australia can be, how damaging and sustained. It’s a trend we can expect to continue to worsen unless we rapidly reduce greenhouse gas emissions.”