Black Summer bushfires ‘were a trigger for La Nina’

The Black Summer bushfire catas­trophe coughed up so much smoke it may have fuelled the global onset of La Nina in 2020, research says.

Firefighters struggle against strong winds in an effort to secure nearby houses from bushfires near the NSW south coast town of Nowra in 2019. Picture: AFP

The Black Summer bushfire catas­trophe coughed up so much smoke it may have fuelled the global onset of La Nina in 2020, according to research published on Thursday.

The report, in peer-reviewed journal Science Advances, said the bushfires were “exceptional” in their severity – pumping out emissions on a scale similar to major volcanic eruptions.

It suggested this led to vast banks of cloud forming over the southeastern Pacific Ocean, which soaked up radiation from the sun and led to a cooling of surface water temperatures.

These disruptions could have helped trigger the start of an ­unusually long La Nina weather pattern, the researchers found.

The bushfires on the eastern seaboard from late 2019 to early 2020 razed forests, killed millions of animals, and blanketed cities in noxious smoke.

A rare “triple-dip” La Nina shaped global weather patterns between September 2020 and March 2023, whipping up a series of devastating tropical cyclones while exacerbating droughts in other parts of the planet.

Researchers John Fasullo and Nan Rosenbloom, from the Nat­ional Centre for Atmospheric Research in the US, used modelling to demonstrate how emissions from the bushfires could shift weather patterns.

Bushfire smoke is laden with particles that act as “condensation nuclei”, which attract water molecules in the atmosphere, seeding the formation of clouds. This blanket of cloud could cause “widespread surface cooling” in the tropical Pacific Ocean, the modelling showed, which is one of the key ingredients for the start of a La Nina.

“The results suggest a potential connection between this emergence of cool conditions in the eastern Pacific Ocean and climate response to the wildfire emissions,” the paper said.

Australian climate scientist Tom Mortlock said the bushfires caused clouds to form in a part of the Pacific that plays a crucial role in global climate regulation.

“The southeast corner of the Pacific is a really sensitive and important area for what goes on with El Nino and La Nina,” he said. “Often we see the first signs of an El Nino or La Nina forming in that part of the ocean.”

Pete Strutton, from the Australian Centre of Excellence for Climate Extremes, said it demonstrated the sheer scale of the bushfires: “We’ve got an event that happened on the land in southeast Australia having an impact on the atmosphere.”

A team of British researchers last year found the Black Summer fires spewed millions of tonnes of emissions, likely aggra­vating the Antarctic ozone hole.

AFP