Australia recorded its hottest day on record on Wednesday, with an average maximum temperature of 41.9C (107.4F), beating the previous record by 1C that had been set only 24 hours earlier.
Tuesday 16 December recorded an average of 40.9C across the continent, beating the previous record of 40.3C set on 7 January 2013. But it held the record for just 24 hours.
Wednesday was even hotter across the country, with the highest maximum temperature reached in Birdsville, Queensland, which hit 47.7C (117.8).
On Wednesday the lowest maximum was 19C at Low Head, Tasmania. On Thursday, Nullarbor in South Australia set the record for the hottest December day on record, recording 49.9C (121.8).
To calculate the average maximum, the Bureau of Meteorology takes the maximum temperatures recorded in about 700 locations, puts them into a grid, calculates an average, and then cross-checks this against its long-term quality controlled record, known as ACORN-SAT.
So why is Australia so hot?
Dr Karl Braganza, manager climate monitoring at the bureau, told Guardian Australia: “Natural variability and global warming are pushing in the same direction. That’s why we have broken records.”
It’s not ‘only natural’
Dr Andrew Watkins, head of long-range forecasts at the bureau, identified three key factors that have pushed temperatures to record levels – two of them natural, and one of them not.
Australia is currently feeling the impacts of one of the strongest Indian Ocean Dipole events on record.
When the IOD is positive, the waters off Australia’s north-west are cooler, dragging moisture away from the continent and leaving very dry conditions.
On the flipside, Watkins said parts of east Africa had seen devastating impacts from flooding rains, in particular in Somalia, Ethiopia and South Sudan.
“That positive IOD has kept things very dry in winter and spring,” Watkins said. “That sets us up with an extremely dry environment. It has been the second driest year to date and the warmest year to date.”
A second natural driver, Watkins said, was a negative phase of the Southern Annular Mode that was kicked off by warming of the atmosphere high above Antarctica.
The SAM had helped drive the extreme heat in NSW and Queensland, Watkins said, adding to the extreme fire danger. This has also brought drier and warmer air across the continent on westerly winds.
SAM events usually only last a few weeks, but Watkins said this event had been present since October.
“All of this is leading to central Australia baking,” he said. “There’s nothing there to evaporatively cool the air.”
He said an example of this heat was revealed in forecast temperatures in recent days of between 43C and 45C for Alice Springs.
“When I see those forecasts I say, ‘wow.’ Because Alice Springs is 550m above sea level. 45C half a kilometre up is pretty insane.
“Meteorologists will say that you get roughly 1C per 100m of elevation so we know that means the air at the surface would have been in the high 40s.”
Climate change pushing heat
Underlying these two major drivers of the heat is climate change – the simple physics of loading the atmosphere with extra greenhouse gases, mainly by burning fossil fuels.
Australia’s latest State of the Climate report shows the country has warmed by just over 1C since 1910, leading to more extreme events.
Watkins said: “That long-term warming sees the bar lifted up so that it’s easier to get extreme conditions now than it was 50 or 100 years ago,”
“One part of me says that this is amazing but then another says that we have seen this in other parts of the world so we’re not especially surprised.”
He pointed to France’s heatwave of June 2019, when Montpellier hit 43.5C, breaking its previous all-time heat record set in August 2017 by a huge 5.8C.
“I’m not sure we are shocked by much any more.”
Dr Sarah Perkins-Kirkpatrick, a climate scientist at the University of New South Wales specialising in extreme events, said climate change had given the natural drivers of Australia’s record -breaking heat “extra sting.”
She said without the extra CO2 in the atmosphere “it would still have been warm”, but, she added: “I doubt very much we would have seen a record on Tuesday and then another one on Wednesday. And we are still at the beginning of the summer with a long way to go.”
On Thursday, she was driving through thick smoke haze in north-west Sydney with her family.
She said: “It is frightening and a little frustrating, but this is what climate scientists have been saying for decades.
“I’m bordering on saying ‘I told you so’ but I don’t think anyone really wants to hear that.”