Large swathes of New South Wales and southern Queensland will face catastrophic weather events over the next few months. The reason is Antarctica's westerly winds, which control the Australian climate, are impacted by 'sudden stratospheric warming.'
As a result, the direst prediction is a change in Australia's rainfall patterns. The likely outcome is drought, desertification, mass deaths of livestock, plants, fish and other wildlife, out of control fires and unbearable heat.
Every winter, westerly winds – often up to 200km per hour – develop in the stratosphere high above the South Pole and circle the polar region. The winds develop as a result of the difference in temperature over the pole (where there is no sunlight) and the Southern Ocean (where the sun still shines).
As the sun shifts southward during spring, the polar region starts to warm. This warming causes the stratospheric vortex and associated westerly winds to gradually weaken over the period of a few months.
However, in some years this breakdown can happen faster than usual. Waves of air from the lower atmosphere (from large weather systems or flow over mountains) warm the stratosphere above the South Pole, and weaken or “mix” the high-speed westerly winds.
Very rarely, if the waves are strong enough they can rapidly break down the polar vortex, actually reversing the direction of the winds so they become easterly. This is the technical definition of “sudden stratospheric warming.”
Impacts from this stratospheric warming are likely to reach Earth's surface in the next month and possibly extend through to January.
Apart from warming the Antarctic region, the most notable effect will be a shift of the Southern Ocean westerly winds towards the Equator.
For regions directly in the path of the strongest westerlies, which includes western Tasmania, New Zealand's South Island, and Patagonia in South America, this generally results in more storminess and rainfall, and colder temperatures.
But for subtropical Australia, which largely sits north of the main belt of westerlies, the shift results in reduced rainfall, clearer skies, and warmer temperatures.