Black Summer bushfire smoke likely triggered record flooding

The vast plumes of smoke that billowed from the Black Summer bushfires increased cloud cover over the Pacific, cooled sea surface temperatures and likely influenced the formation of the rare triple La Nina weather pattern, which brought record-breaking floods to Australia.

The unprecedented bushfires, which peaked around January 2020, emitted smoke particles into the atmosphere on par with major volcanic eruptions and had a widespread climate impact over years, according to new research in Science Advances.

Sunrise through thick smoke over Parliament House in Canberra in December 2019.Credit: Alex Ellinghausen

Study authors John Fasullo and Nan Rosenbloom, from the US-based National Center for Atmospheric Research, said analysis showed an interaction between the smoke pollution and increased cloud cover, which likely influenced the La Nina event of 2020-22.

The US researchers ran two sets of climate models - one that included the smoke pollution produced by the Black Summer bushfires and the other that did not. They found a significant difference between the two, which suggests the bushfire smoke that blew from Australia’s coastline increased cloud cover over the south-west Pacific and cooled the sea surface.

The smoke’s tiny particles attracted moisture to them, like the process used in cloud seeding, which then increased cloud cover and cooled the surface of the ocean.

“This may become more prevalent under climate change as wildfires are projected to intensify and become more frequent,” the researchers warned.

You’re probably familiar with the El Nino Southern Oscillation cycle over the Pacific Ocean, which affects weather worldwide. For most of Australia, El Nino brings dry weather, while La Nina brings wet weather. It’s one of the most important drivers of unusual weather over the entire globe.

The south-eastern Pacific is where the first signs of an El Nino or La Nina weather pattern form, and this new research suggests the warming ocean “flipped” the climatic conditions into the La Nina phase.

Dr Tom Mortlock, a senior analyst at Aon insurance company and an adjunct fellow at the Climate Change Research Centre at the University of New South Wales, said it was the first time researchers had looked at the effects bushfires on a global scale.

“There has never really been a bushfire big enough to look at this before,” said Mortlock. “We do know there is a causal link between volcanism [volcanic explosions] and ENSO, and this tells us that everything is connected.”

Imagery from the Japanese weather satellite Himawari-8 shows the blanket of bushfire smoke that blew across the Tasman Sea was wide enough to cover all of New Zealand’s South Island.

Most climate change research suggests that extremes in our weather patterns will become more frequent. The effects of El Nino and La Nina could become more pronounced, but this does depend on where anomalous warming occurs across the Pacific.

Professor Pete Strutton, from the Institute for Marine and Antarctic studies at the University of Tasmania, said it showed regional events like bushfires could have global implications.

“It’s an example of long-term climate change having a feedback effect on climate variability,” said Strutton. “If it weren’t for those fires we might have flipped back to El Nino in the years that followed.”

“We know from looking at historical insurance loss data that bushfire losses are correlated to periods of El Nino. There is now a 60 per cent chance that El Nino will begin to form this winter, peaking in spring and summer.”

Australia’s Bureau of Meterology says there is a 50 per cent chance of an El Nino occurring later this year, with models showing it would be under way by August.

But Strutton said the consensus from scientists at the World Meteorological Organisation is that there is a 60 per cent chance El Nino will form. “It’s looking more likely than not,” he said.

The Black Summer period was the culmination of several years of hot and dry conditions in Australia.

The bushfires spawned an increase in rare fire-induced thunderclouds, known as “pyrocumulonimbus” clouds.

This “super outbreak”, as scientists called it, injected plumes of smoke into the stratosphere, a layer of the atmosphere that starts about 15 kilometres above the Earth.

There, the smoke plumes created self-sustaining vortexes that circled the globe.

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