High above Antarctica, a polar vortex swirls. When it’s in robust shape, its icy winds swirl in a circular pattern, keeping a ring of freezing weather contained above the frozen continent.

This year, something else is happening. As warmer than average air temperatures have been recorded above Antarctica, the polar vortex has weakened, causing it to lose stability.

As its circular pattern slackens, its edges have pushed into southern Australia, creating icy conditions and freezing winds.

On Tuesday, Sydney shivered through an apparent temperature of 0.6 degrees, despite recording 7.6 degrees at 7.30am. In Melbourne on Thursday, the temperature plummeted to minus 1 at Avalon Airport at 7.40am.

Climate scientist Dr Martin Jucker, of the University of NSW, said recent warming near Earth’s surface had pushed warmer air into the stratosphere – to an altitude of about 30 kilometres – above Antarctica.

Last month, air temperatures warmed suddenly more than 20 kilometres above eastern Antarctica by about 50 degrees, a phenomenon known as sudden stratospheric warming.

ABC meteorologist Tom Saunders said the phenomenon had never before been observed in winter.

The effects of climate change on global surface temperatures are clear: it was 1.1 degrees higher in the decade between 2011 and 2020 than it was between 1850 and 1900, and greenhouse gas emissions have continued increasing.

However, Jucker said, scientists were yet to establish a link between a sudden stratospheric warming and climate change. “Something needs to create those disturbances at the surface first, and that might be impacted by climate change,” he said. “We don’t know.”