How climate change accelerated spring winds

Strong winds in eastern Australia this week are being driven by climate change interfering with jet streams, the powerful high-altitude winds that encircle the globe.

Australia’s two jet streams – subtropical and polar – have combined over the continent’s south-east. This has caused strong winds on the surface of the earth that have brought a cold front to Victoria and southern NSW, and flipped between hot desert air and cool winds over Sydney and further north.

Wild winds have battered Victoria and NSW, fuelling bushfires and felling trees and powerlines, but the strong winds may have also generated a record amount of wind energy. This comes as official figures released on Monday show last month was Australia’s hottest August on record.

Dr Milton Speer, a visiting fellow in the School of Mathematical and Physical Sciences at the University of Technology Sydney, said: “The jet streams are the main thing affecting the weather in south-eastern Australia at the moment.”

The jet streams blow from west to east, driven by the earth’s rotation. They are at their strongest about 10 kilometres above the surface, usually about 200km/h stretching across a horizontal area of 100-200km. They are used by intercontinental jetliners travelling eastward to save on fuel. The less intense, yet strong, surface winds caused by the polar jet stream have been known as the Roaring Forties by sailors for centuries.

Speer said Bureau of Meteorology data showed the polar jet stream moving at 200-280km/h as of 4am on Monday, and stretching horizontally across several hundred kilometres to affect a large swath of the southern part of the continent. The subtropical jet stretched 150-200 kilometres with weaker speeds and was almost merged with the polar jet on the NSW Mid North Coast.

Speer said the subtropical and polar jet streams were usually split during the cooler months from about April to October. While they came together in summer, they usually sat over the Southern Ocean below the continent, he said.

Speer said the latest research suggested that the extent of sea ice melting in Antarctica this winter had pushed the polar jet further north, while the marine heatwave in the tropics had pushed the subtropical jet further south. The result was that the two had combined over south-eastern Australia, amplifying the effect.