By Padraig Collins For Daily Mail Australia
14:02 11 May 2023, updated 14:17 11 May 2023
- Shock new scientific theory has emerged
- Researchers explain what caused La Nina
A shock new theory has emerged as a likely explanation for why Australia’s last three summers were far wetter and cooler than normal, bringing devastating flooding and loss of life.
Though the direct explanation is it was caused by the very rare occurrence of a triple-dip La Nina weather pattern, there may be a surprising factor behind that.
Scientists have found that smoke pollution from the months-long ‘Black Summer’ bushfires of 2019-2020 may have contributed to the La Nina pattern that hit Australia three years running.
In a study published in the Science Advances journal, researchers ran climate models with and without bushfire emissions to determine the role the fires played.
What they found was astonishing. ‘In fact, we underestimated the effects, if anything, of the wildfires,’ lead author Dr John Fasullo of the US-based National Centre for Atmospheric Research said.
‘But what we found in the initial two years itself was actually pretty interesting – we have this La-Nina-like response,’ he told the ABC.
The study was sparked by research into emission reductions during lockdowns caused by the Covid-19 pandemic.
But the researchers thought the 2019-2020 bushfires may have had a bigger effect on the climate than the drop in emissions due to pandemic lockdowns.
It is thought the Black Summer fires were the first widespread enough to affect climate models, but the findings could provide an insight into the link between large bushfires and climate events of the past.
The Black Summer bushfires, which burned with an abnormally high intensity and size, pumped huge amounts of smoke aerosols into the atmosphere.
It was so intense that it was on par with major volcanic eruptions and could be seen from space.
At one point in December 2019, there were more than 100 fires burning at the same time in NSW alone.
Dr Fasullo said the emissions caused clouds to become brighter, thicker and longer lasting, which then created a cooling effect across the southern hemisphere.
In turn, this was likely to have created favourable conditions for the La Nina to form in 2020, by helping to move a large tropical cloud band northwards and allowing trade winds to come in underneath it.
‘The trade winds over the equator lead to this steep ocean upwelling, and that is a La Nina event,’ Dr Fasullo said.
He added that the bushfires roughly doubled the chances of a prolonged La Nina.
‘They certainly added in a material way to both the probability of La Nina and also the intensity of La Nina for at least two years.’
The La Nina’s in 2020, 2021 and 2022 dominated Australia’s weather patterns and brought devastating and record-breaking flooding in the eastern states.