Australia’s weather – dominated for three years by La Niña conditions in the Pacific that soaked the east of the country – could be about to flip into a hotter and drier phase.
But what might the potential arrival of La Niña’s hotter and drier cousin, El Niño, mean for Australians still recovering from the floods of recent years, and our ecosystems?
Some scientists are fearing the worst, with an El Niño raising the chances of dangerous bushfire weather, longer and fiercer heatwaves and severe coral bleaching across the Great Barrier Reef.
Is El Niño coming?
Conditions in the tropical Pacific such as the location of warmer water and the strength of trade winds are part of what is known as the El Niño southern oscillation (Enso) – a mode that swings between neutral, El Niño and La Niña.
This week the Bureau of Meteorology said Enso would move from La Niña to neutral in February.
But there is still some uncertainty about whether the climate will shift into an El Niño state later this year.
The bureau’s own climate model is predicting an El Niño by June this year, but this comes with a large caveat.
While six other models from other agencies around the world show conditions heading in the same direction, they do not show temperatures in the Pacific high enough by June for an El Niño.
Climate scientists said all models at this time of year are afflicted by the “autumn predictability barrier” in the Pacific.
That means meteorologists have to wait a few months to have confidence in the forecasts, and the bureau says “outlooks through and beyond autumn should be viewed with caution”.
But Dr Wenju Cai, an Enso expert and chief research scientist at CSIRO, says El Niños lasting two years often follow triple La Niñas.
“There’s a high chance of a few El Niños coming up, even if it’s not immediate. We are due a few warm years,” he say.
More extreme impacts
Cai says climate models are suggesting that as the world keeps warming, there will be more extreme La Niñas and El Niños, less neutral years, and their impacts will be more extreme.
The drying and heating impacts of El Niños, he says, are being superimposed on human-caused global heating.
“Heatwaves are worse and droughts are longer, deeper and harder to break,” he says.
Globally, the last strong El Niño coupled with ongoing global heating helped deliver the warmest year on record in 2016. There is also evidence from one study that weather events and fires driven by El Niño can cause an increase in the amount of CO2 in the atmosphere.
Dr Andrew King, a climate scientist at the University of Melbourne, says as the climate warms, an El Niño “will really increase the chance of a record hot year globally.”
But he says for Australia, no two El Niños are the same and they do not guarantee extreme heat or drought for Australia, but do increase the risk.
Rising bushfire risk
The Black Summer bushfires of 2019 and early 2020 were devastating for communities across the south and east of Australia and killed or displaced billions of native animals, pushing threatened species to the brink.
Those fires came after two years of weak El Niño conditions alongside cooler than average ocean temperatures in the eastern Indian Ocean that also promote drier conditions in southern and eastern parts of the country.
Those conditions in the Indian Ocean often, but not always, coincide with El Niños.
The three years of La Niñas have seen strong vegetation growth which could turn into lots of fuel for fires if conditions turn drier and hotter, Prof David Bowman, a bushfire expert at the University of Tasmania, says.
“The propensity for landscapes to burn is going to be jaw-dropping,” Bowman says.
“We could unfortunately see very serious fire activity and for the public, that’s very difficult to wrap your mind around when it’s been so wet. But you will see these landscapes move into highly flammable states.”
Bowman says the wet years have promoted grass growth, which he said was “the petrol of bushfire fuel” that burns fast and intense.
“Of course we’re all worried [about an El Niño] because we’ve been living with these other threats of flooding. But it’s going to come roaring back at us.
“You will get that kick in global heating for the El Niño and it will absolutely no question – because of the fuel – result in an increase in fire activity.”
Great Barrier grief
Tropical reefs around the world – including Queensland’s Great Barrier Reef – face higher risks of coral bleaching during El Niño years.
Bleaching, if severe, can kill corals. Studies have shown corals that survive and regain their colour can suffer “sub-lethal” effects such as slower growth rates, disease and less ability to reproduce.
Historically, the cooler temperatures and cloud associated with La Niñas have given the Great Barrier Reef a recovery period from rising ocean temperatures due to global heating.
So marine scientists were shocked last year at the first mass coral bleaching event in a La Niña year. They expressed dread at what might be in store with the next El Niño.
“El Niño hugely increases the risk of an extreme bleaching event,” Prof Terry Hughes, a global expert on coral bleaching at James Cook University, says.
The Australian Institute of Marine Science’s latest report card on the reef said the cooler years of La Niña had helped the reef to recover, with large numbers of fast-growing corals underpinning the rise in coral coverage.
But, as Aims and Hughes have pointed out, those same corals are the most susceptible to bleaching.