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Black Summer fires may have helped trigger damaging triple La Nina

Long-range weather forecast, June-August

Source: Bureau of Meteorology

The past two years of heavy rain and record flooding across Australia’s east coast was exacerbated by the Black Summer bushfires, a study has found.

Research released on Thursday links bushfire smoke to extra cloud cover over the south-eastern Pacific Ocean and cooler sea surface temperatures, which then influenced La Nina.

Eastern Australia has had several years of disastrous flooding during the rare weather phenomenon. When a La Nina formed in late 2022, it was the first time this century that the weather pattern had been seen in three consecutive northern hemisphere winters – something known as a “triple-dip” La Nina.

The research, published in Science Advances, shows the Black Summer bushfires in 2019 to 2020 emitted as many aerosols into the atmosphere as major volcanic eruptions.

Researchers behind the study ran climate models with and without bushfire emissions to determine the role of the devastating bushfires that spread up and down Australia’s east coast.

“In fact, we underestimated the effects, if anything, of the wildfires,” Lead author John Fasullo from the US National Centre for Atmospheric Research said.

“What we found in the initial two years itself was actually pretty interesting – we have this La-Niña-like response.”

Dr Fasullo said the influence of the bushfire emissions lasted well beyond the time it took for smoke particles to clear.

The ongoing effect caused clouds to become brighter, thicker and longer lasting, he said. In turn, that had a cooling effect across the southern hemisphere, setting off a chain reaction of events that was likely to have created favourable conditions for the La Niña to form in 2020.

UNSW Climate Change Research Centre adjunct fellow Dr Tom Mortlock said it was the first time a bushfire had been big enough to affect climate models.

He said years of above-average rainfall and fewer bushfires since the crisis meant there was a significant amount of fuel growth ready to burn when warmer weather arrived in the form of El Nino.

“Bushfire losses are correlated to periods of El Nino,” Dr Mortlock said.

“There is now a 60 per cent chance that El Nino will begin to form this winter, peaking in spring and summer.”

In its latest long range outlook, released this week, the Bureau of Meteorology said six of the seven international models indicated El Niño thresholds would be met or exceeded from July, with all models meeting thresholds by August.

-with AAP

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