Smoke from Black Summer may have fuelled ‘unusual’ years-long La Niña

lThe Black Summer bushfires of 2019-20 may have produced so much smoke it fuelled the years-long La Niña responsible for flooding rains, a new study suggests.

The new model-based study from the US National Centre for Atmospheric Research, published in Science Advances, found smoke emissions from catastrophic bushfires enhanced cloud cover over the southeastern Pacific Ocean.

This cooled sea surface temperatures and influenced the La Niña event of 2020-22, which was considered a "rare" triple-dip event.

Researchers explained the La Niña event was "unusual in many respects" and caught forecasters off-guard.

"Most notably, it did not follow a major El Niño event, with weak SST (sea surface temperature) anomalies existing in early 2020, and therefore was not accompanied several months in advance by reflected upwelling Kelvin waves from the western Pacific boundary typically associated with La Niña," the paper states.

"The event was also poorly forecast, with major prediction centres such as National Oceanic and Atmospheric Administration–Climate Prediction Center (NOAA-CPC) issuing guidance for ENSO-neutral conditions as late as June 2020.

"At this time, the emergence of ocean cooling in the eastern Pacific Ocean led some forecasters to favour a La Niña event for late 2020.

"The results here suggest a potential connection between this emergence of cool conditions in the eastern Pacific Ocean and the climate response to Australian wildfire emissions."

Dr Tom Mortlock, a senior analyst at Aon and adjunct fellow at the UNSW Climate Change Research Centre, said the findings are a world-first.

"A long line of research has shown that volcanic eruptions can affect La Niña through a similar process, but this is the first time a bushfire event has been widespread enough to have an impact in climate models," he said.

"In fact, if we look further back in the past, we can see a relationship between periods of volcanism and tropical cyclone activity in Australia, because of the same causal process.

"It further highlights the interconnectivity of the climate system, and this doesn't stop over the ocean.

"The prolonged La Niña, above average rainfall, and absence of bushfires on the east coast has led to high fuel growth and preconditions the landscape for burning when El Niño comes along".

The comments come after the Bureau of Meteorology (BoM) declared an El Niño watch, saying there's a 50 per cent likelihood the brother phenomenon to La Niña will form.

If it does, Australia would see hot, dry conditions, which bring an increased risk of drought and bushfires.

A total of 33 people lost their lives in the Black Summer fires, which burned 24 million hectares of land across every Australian state and territory.

Smoke from the bushfires was linked to the deaths of an additional 450 people, a royal commission heard.

Three billion animals are estimated to have died and 3000 homes were lost.

Have a story? Contact Raffaella Ciccarelli at [email protected].

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