Another study on what cause the triple La Nina says Australia's bushfires were to blame

Their latest theory is that Australia's bushfires in 2019-20 might have caused it.

It comes hot on the heels on research which blamed the global event on the world's oceans.

A warm tropical Pacific combined with the Indian and Atlantic oceans to spark the long La Nina, research found.

Scientists have long thought multiyear La Nina events were triggered as a rebound from preceding extreme El Nino events.

Forecasters agree Australia is heading into an El Nino later this year.

International climate models suggest further warming of the Pacific Ocean is likely this year.

From July, six of the seven international models used by the Bureau of Meteorology indicate El Nino thresholds for sea surface temperatures "will be met or exceeded, with all models meeting thresholds by August".

While we wait anxiously on that, some scientists across the world are blaming Australia's bushfires for their weather extremes - from three years of drought in California to floods back home.

A study published in the past week suggests smoke emissions from the 2019-20 bushfires increased cloud cover over the southeastern Pacific Ocean, cooling sea surface temperatures to trigger the La Nina event from 2020-22.

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The bushfires, which peaked around January 2020, emitted particulate aerosols into the atmosphere on par with major volcanic eruptions, the study said.

Recent studies suggest emissions from volcanic eruptions may produce a climate response similar to the La Nina cooling phase of ENSO - surface cooling and a northward shift of intertropical convergence zone wind patterns in the tropical Pacific.

After the bushfires, cooler surface temperatures were observed across the tropical Pacific and overlapped with the onset of the unexpected 2020-22 La Nina event, this latest research from the US National Center for Atmospheric Research found.

"Few studies have explored the extent to which wildfire emissions may have contributed to this cooling trend," the study found.

Researchers ran computer models to observe the difference with and without emissions as observed by satellites during the 2019-20 Australian bushfires.

The researchers say the found cooling primarily caused by an increase in stratocumulus cloud cover over the southeastern tropical Pacific, brought on by an abundance of condensation nuclei from wildfire emissions.

Enhanced cloud cover caused widespread surface cooling and a northward shift of the ITCZ (Intertropical convergence zone), which "potentially affected the onset" of La Nina in late 2020.

"This analysis illustrates an interaction between biomass aerosol forcing and ENSO that may become more prevalent under climate change as wildfires are projected to intensify and become more frequent," the authors warned.