Climate Change

Black Summer: Australian wildfires linked to La Niña’s three-year streak, finds study

La Niña would have occurred without the 2019-2020 wildfires, but would have been short-lived and weaker

By Rohini Krishnamurthy
Published: Thursday 11 May 2023
The horrific 2019-2020 Australian bushfire burnt more than 46 million acres of land. Photo: iStock_

The horrific 2019-2020 Australian bushfire, which burnt more than 46 million acres of land, was likely responsible for La Niña’s three-year streak, according to a study. The event is known in Australia as the ‘Black Summer’.  

La Niña, or the “cold event”, is a climate pattern in the Pacific Ocean known to affect weather worldwide. During La Niña, there is large-scale cooling of the ocean surface temperatures and changes in the tropical atmospheric circulation.

This three-year run that ended in 2023 is considered rare, noted the study published in journal Science Advances. A triple-dip La Niña was recorded in 1998-2001, 1973-1976, and 1954-1956. 

Read more: ‘This crisis has been unfolding for years’: 4 photos of Australia from space, before and after the bushfires

“Many people quickly forgot about the Australian fires, especially as the COVID-19 pandemic exploded, but the Earth system has a long memory and the impacts of the fires lingered for years,” John Fasullo, National Center for Atmospheric Research and lead author of the study, said in a statement.

La Niña conditions typically emerge in the year following major volcanic eruptions in the southern hemisphere, the paper read. Sulphur aerosols from volcanic eruptions reach the stratosphere, where they scatter solar radiation, cooling the planet.

Fasullo and his colleagues wanted to understand how the 2019-2020 bushfires that burned an area roughly the size of Syria impacted the climate pattern.

So the team ran two batches of simulations using a computer model. The first simulation considered the emissions from the wildfires as observed by satellite, while the other included the average wildfire emissions. 

The wildfires quickly blanketed the Southern Hemisphere, the first simulation found. The aerosols that formed from the smoke impacted the clouds.

“The cloud drops become smaller and longer-lived due to the smoke, reflecting more sunlight to space and cooling an essential part of the planet, the southeastern subtropical Pacific Ocean,” Fasullo told Down To Earth.

Read more: Unusually long La Niña displaced record number of people in 2022

The results suggest a potential link between the emergence of cool conditions in the eastern Pacific Ocean and the climate response to Australian wildfire emissions, according to the researchers. 

La Niña would have still occurred without the bushfires — but it would have been short-lived and weaker, Fasullo explained. Further, the researchers suspect such interactions could become more prevalent as wildfires are predicted to become more intense and frequent with climate change.

He also speculates that such interactions between wildfires and La Niña may have happened before.

The team now plans to look at historical events for similar instances in the past. “We also want to look at the effects of northern hemisphere fires to see if similar interactions might take place,” Fasullo noted.

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