The Australian summer is undergoing a "total transformation", as scientists warn climate change made a recent blistering heatwave five times more likely.
Australia's southern states sweltered during early January through the worst heatwave conditions since the summer of 2019-2020, a period scarred by devastating bushfires.
Peak temperatures in the 40s across much of southeast Australia constitute the sort of extreme event that would have occurred just four times a century before human-induced global warming.
Now, the World Weather Attribution says similarly intense three-day heatwaves can be anticipated every five years.
If the world warms 2.6C above pre-industrial averages as predicted under existing policy settings, such extreme heat events could strike every second year by the end of the century.
A 'major shift' in heatwave prevalence
Australian National University professor of climate science Sarah Perkins-Kirkpatrick said the major shift in heatwave prevalence underlined the urgency to cut emissions and adapt to warming already baked in.
"It is a total transformation of the Australian summer," Perkins-Kirkpatrick said.
"What we once considered an extraordinary heat event is now something a primary school student today will likely experience several times before they finish high school."
Health resources were stretched during the heatwave in early January as temperatures above 40C were recorded in the southern states on multiple days, with one hospital reporting a 25 per cent bump in emergency admissions.
Victoria was hit hard, with Melbourne Airport recording a maximum temperature of 44C and a state of disaster declared when strong winds fanned several out-of-control fires across landscapes left bone-dry after days of severe heat.
One life was lost to the fires that also burnt more than 900 structures and killed tens of thousands of sheep and cattle.
Ben Clarke, a Centre for Environmental Policy researcher at Imperial College London, said extreme heatwaves were on track to become the "norm rather than the exception" in Australia.
"One of our most striking findings is that the impact of climate change far outweighed natural climate variability — including a weak La Niña, which typically signals cooler temperatures," he said.
Australia's weather is heavily influenced year-to-year by the natural cycle known as the El Niño-Southern Oscillation.
A La Niña is associated with wetter conditions and lower daytime temperatures and an El Niño with drier conditions and higher maximums during the day.
Extreme heat is known as a "silent killer" that causes more deaths than floods, bushfires, cyclones and storms combined in Australia.
'Urgent need' to adapt our cities
Australia's own national climate risk assessment suggests heatwave deaths could skyrocket by more than 400 per cent in Sydney and more than 250 per cent in Melbourne under 3C of warming.
Researchers are increasingly linking high temperatures to a range of worse health outcomes, including mental health concerns and more common and severe sleep apnea.
Emmanuel Raju, director of the Copenhagen Centre for Disaster Research at the University of Copenhagen, said the burden of extreme heat fell heaviest on the most vulnerable.
"The elderly, those in poor-quality housing or without cooling, and people with pre-existing health conditions," he said.
"We urgently need to adapt our cities and our health systems to this new reality."
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