While Australians thought they were in for a wet spring and summer, a rapid shift in temperature above Antarctica could change the outlook.
Last week, around 30km above the surface of the southern continent, close to the hole in the Earth's ozone layer, a dramatic change began to occur.
Waves of air surging upwards crashed through the winds in the stratosphere, losing energy suddenly and forming a large pool of hot air that climbed more than 30C within the span of a week.
The event is known as a Sudden Stratospheric Warming (SSW) and due to the usual extreme strength of the winds above Antarctica, it's rare in the Southern Hemisphere.
But when it happens, SSW can have significant consequences for what we experience on the ground in Australia.
Dr Martin Jucker, a lecturer at the Climate Change Research Centre at the University of New South Wales, told SBS News it's not entirely clear how this happens — but the consequences of it have been felt acutely in Australia in the past.
"We know that if this bunch of air at 30 kilometres warms, we know that after that, surface weather patterns behave differently," he said.
"It causes often warmer and drier than usual conditions in south-eastern Australia. It didn't cause the bushfires in 2019, but it made them worse because it just made conditions even worse — even more fire-prone."
What is it doing to our weather right now?
Senior climatologist from the Bureau of Meteorology (BoM), Zhi-Weng Chua, told SBS News there are some signs of the SSW's effects in the weather many Australians will be feeling over the next two weeks.
Most of mainland Australia has already had hotter weather in the past week.
In NSW, temperatures over the weekend were around five to 10C above average.
Over the next fortnight, south and eastern Australia will continue to experience stretches of hot weather (after a brief cool dip in the coming days), with temperatures in South Australia likely to be between eight and 12C above average.
"It's hard to really atrribute [the hot weather] to one factor but it's likely that the SSW is playing into some of these temperatures," Chua said.
What does it mean for spring and summer?
The long-range effect of SSWs on the weather we experience in Australia can be difficult to predict, as it involves a multitude of factors.
For example, an SSW that formed in July last year was relatively short-lived because it occurred in winter and there wasn't enough sunlight to compound the heating effects.
The consequences of the current SSW are also unclear, said Jucker. While the spring sunlight is adding to the impact of the waves hitting the stratosphere and creating a greater heating effect than what was seen last year, there are competing predictions for what will happen to Australia's weather in the coming months.
While SSWs can bring significantly hotter, drier weather to Australia (as experienced in 2019), the Bureau of Meteorology recently released its long-range forecast predicting above-average rainfall across most of the eastern half of the country and the possibility of a weak La Niña forming.
One of the main predictors of this wet weather is what's known as the negative Indian Ocean Dipole — an atmospheric and ocean pattern that emerges when the eastern side of the Indian Ocean surrounding Australia is hotter than the western side.
But Jucker said this is creating a conflicting scenario where "the stratosphere would like to make it dry but the oceans would like to make it wetter".
At the moment, the BoM has not predicted any major changes to its wet long-range forecast caused by the SSW past the next two weeks. But Chua said this could change and the BoM updates it long-range forecasts weekly.
Climate change
As for whether the changing climate will increase the likelihood of SSW events in the southern hemisphere in the future, the interaction between the two is difficult to pinpoint, Jucker said.
Earlier this month, the National Climate Risk Assessment published a grim outlook for Australia's climate future, including more deaths from heat-related issues and millions placed at risk of coastal flooding.
The assessment said no Australian community will be immune from climate risks it called "cascading, compounding and concurrent".
Australia has already reached 1.5C of warming above pre-industrial temperatures.
Jucker said his own research has found that — perhaps contrary to what might be expected — the stratosphere will cool as climate change continues, leading to fewer rapid heating events above Antarctica.
However, that modelling did not include the warmer Australian offshore temperatures at the moment and warmer seas could actually lead to more SSWs by sending more atmospheric waves upwards into the stratosphere.
"It's a tough one to say," Jucker said.
"Right now, I would think that these really warm ocean temperatures, which have been causing quite weird weather for the last two years or so, they might have a role in [creating more SSWs]."
