| | | Australia’s climate is notorious for its volatility, but this summer’s high temperatures — peaking at close to 120 degrees Fahrenheit in December — and subsequent fires have still been outliers.
The country itself spans a region from the tropics in the north to more temperate climates in the south, with deserts in the middle. It also sits between two major oceans and is buffeted by the shifting circulation patterns of both. So the weather over the continent can change drastically year to year and become hard to predict. Still, Sarah Perkins-Kirkpatrick, a senior lecturer at the Climate Change Research Centre at the University of New South Wales, Sydney, explained that there were warning signs that this year’s summer in Australia would get brutally hot.
One signal was that the Indian Ocean Dipole, the cycle of the temperature gradient between the eastern and western parts of the Indian Ocean, was in its positive phase this year. That led to much less rainfall over Australia as prevailing winds pushed moisture gathering above the Indian Ocean away from the continent in the spring.
Another alarm bell this year was the Southern Annular Mode. This describes the movement of the circular belt of wind around Antarctica as it shifts north or south. It’s in its negative phase right now, bringing dry conditions to Australia. This year, it also blended with a surge of heat in the stratosphere, channeling gobs of hot, dry air to southern Australia.
And while Australia’s annual monsoon rains in the northern part of the country packed a devastating wallop in February, causing dangerous flooding in the state of Queensland, they were also behind schedule. That allowed more heat to accumulate over the central part of the country this year.
“So there was lots going on in terms of natural climate variability for this season to be quite hot,” Perkins-Kirkpatrick wrote in an email.
At the same time, there were longer-term factors at work. One of them is that much of Australia is facing a severe drought, spurred by three winters in a row with very little precipitation.
“That’s never happened in the instrumental record,” Michael Roderick, a climate researcher at the Australian National University told the Sydney Morning Herald in November. “They’ve never really had two failed winters in a row.”
With drought conditions, there is less moisture evaporating in the heat, a phenomenon that usually has a cooling effect.
All the while, the climate is getting hotter. “Australia’s climate has warmed by just over 1° C since 1910, leading to an increase in the frequency of extreme heat events,” according to the Australian Bureau of Meteorology’s 2018 State of the Climate report. This has also led to more rainfall in northern Australia, but less in the southeast, where most Australians live. |
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