Abnormally hot days may hit Australia’s south-east after rare sudden warming over Antarctica

Phenomenon extremely unusual in southern hemisphere and last occurred in 2019 when it contributed to worsening of black summer bushfires

A rare rise in stratospheric temperatures over Antarctica could influence weather into summer, with previous events driving hotter and drier conditions for south-east Australia.

The phenomenon – called sudden stratospheric warming – is extremely unusual in the southern hemisphere.

There have only been three moderate to major events in the past 45 years – in 1988, 2002 and 2019 – a Bureau of Meteorology spokesperson said, with the latter contributing to a worsening of the black summer bushfires.

In early September this year, air temperatures 30km above the Southern Ocean and Antarctica began to climb, and are now sitting about 30C warmer than average, according to Dr Martin Jucker, a senior lecturer in atmospheric science at the University of New South Wales.

“Normally it’s about minus 50C, so now it’s minus 20C – it’s still pretty cold,” Jucker said.

The warming is accompanied by a slowdown in the powerful winds above the Earth’s polar regions, called the polar vortex. Usually those winds are about 200km/h but are now about 100km/h.

Those changes are likely to drive warmer and drier weather patterns at the surface, particularly in NSW and Victoria. But the effects this time around are partly unknown, given the Bureau of Meteorology’s forecast for wetter conditions.

“So there is a balancing act between these very warm ocean temperatures, which would drive wet weather for us, versus the stratosphere, which would drive dry weather,” Jucker said. “Who wins? I don’t know.”

According to the bureau, weather changes associated with past stratospheric warming events have had their strongest effects in New South Wales and southern Queensland, with increased springtime temperatures and less rainfall.

Ben Domensino from Weatherzone said the sudden stratospheric warming could influence a climate driver called the southern annular mode. This could increase the chance of abnormally hot days in southern Australia and make drier-than-average conditions over eastern Australia more likely.

While unusual in the southern hemisphere, sudden stratospheric warming events are more common in the northern hemisphere, occurring about six times a decade.

In Australia, these events have greatest impact when they occur in spring.

“While the current stratospheric warming over the South Pole is substantial, the degree of warming is currently weaker than that which occurred in the spring 2019 and 2002 events,” the bureau’s spokesperson said.

Jucker said there is one positive from stratospheric warming. As temperatures rise above the threshold for ozone destruction, the size of the ozone hole reduces.

Cover photo:  A rare rise in stratospheric temperatures over Antarctica is likely to drive warmer and drier weather in Australia, particularly in the south-east. Photograph: Tracey Nearmy/AAP