Billowing smoke from the Black Summer bushfires may have contributed to the rare triple La Nina that has caused record Australian flooding, a US study has shown.

Climate scientists at the National Centre for Atmospheric Research (NCAR) in Boulder, Colorado, incorporated satellite data for bushfire smoke into model simulations, with results suggesting the bushfires were an important contribution to the 2020-2022 strong La Nina events.

“Many people quickly forgot about the Australian fires, especially as the covid pandemic exploded, but the Earth system has a long memory, and the impacts of the fires lingered for years,” scientist and study lead author John Fasullo says on an NCAR news website.

The research published in Science Advances says the “Australian wildfire season” that started in late 2019 and continued into the next year was exceptional in both its severity and particulate emissions.

“Coupled simulations of its climate impact also show responses in clouds and radiation on a planetary scale, similar to those simulated for a major volcanic eruption, suggesting the potential for a broad range of climate responses,” it says.

The work explores the influence of the fires on sea surface temperatures in the tropical Pacific Ocean and analyses the mechanisms connecting the two.

The bulk of bushfire emissions didn’t reach the altitudes of those caused by volcanic eruptions and acted differently to influence the climate. But the emissions brightened cloud decks across the Southern Hemisphere, especially off the coast of Peru, and the ultimate net result, according to the study, was a cooling of the Tropical Pacific Ocean, where La Ninas form, over multiple years.

Aon Senior Catastrophe Research Analyst Thomas Mortlock says the link between particulate matter in the atmosphere and La Nina conditions in the Pacific is not new, with the relationship between volcanism and active periods of floods and cyclones marked in Australia’s paleo record.

“However, we've not really had a bushfire recent enough and large enough to undertake an attribution study like this before,” he says in a LinkedIn post.

“If anything, this talks to the interconnectivity of the climate system and how landscape, atmosphere and ocean, are all linked - however much it might please us to view them separately!”

Mr Mortlock says the research is a robust piece of attribution science undertaken by a respectable group in the US, using a respectable ensemble of climate models and with caveats well-articulated in the paper.

The research can be seen here.