Scientists say climate change made the January heatwave in south-eastern Australia five times more likely
Temperatures exceeded 40°C in major cities, straining hospitals and increasing bushfire risk
Researchers warn such extreme heat could become a regular event within decades
The intense heatwave that struck south-eastern Australia in the second week of January 2026 was made significantly more intense and five times more likely by global warming and consequent climate change, according to a new analysis by the World Weather Attribution (WWA) group published January 22, 2026.
WWA is a consortium of climate scientists from around the world that conducts research to understand and quantify the role played by human-induced climate change in the occurrence, frequency and intensity of extreme weather events, known as attribution studies.
The heatwave occurred despite weak La Niña conditions in the equatorial Pacific Ocean, which typically bring cooler temperatures to parts of Australia. The study found that in a warmer future — with global temperatures rising by around 2.6 degrees Celsius (°C) — heat events of this intensity could occur as often as once every two years.
Between January 5 and 10, maximum temperatures exceeded 40°C across multiple major cities, including Melbourne and Sydney, according to the analysis. Conditions were even more extreme in the states of Victoria and New South Wales, with Melbourne recording a maximum temperature of 44.4°C on January 9.
On the same day, brief but strong winds passing over dry and overheated parts of Victoria created ideal conditions for the rapid ignition and spread of bushfires, placing lives and property at risk. The study noted that the conditions were comparable to those during the 2009 Black Saturday bushfires, which killed 173 people, injured more than 400 and destroyed over 400,000 hectares of land.
The heatwave also had a significant impact on public health. One hospital in Melbourne reported a 25 per cent increase in emergency admissions, according to a press release accompanying the report.
“During recent heat events, emergency departments in Melbourne and Sydney reported sharp increases in the number of patients, particularly among elderly people, those living in overheated buildings without access to cooling, outdoor workers, and individuals with pre-existing conditions,” said the report. “In regional South Australia, clinicians also reported worsening mental health presentations linked to extreme heat.”
Heatwaves cause more deaths in Australia than all other natural hazards combined, the report said. It noted that vulnerability to extreme heat has shifted over time — from primarily elderly people living alone to populations facing socio-economic disadvantage and chronic illness, including homeless people and migrants, “highlighting the need for adaptive, equity-focused heat-health policies,” the report said.
To assess the role of climate change in intensifying the heatwave, the researchers defined a three-day extreme heat event in south-eastern Australia and analysed observed maximum temperatures, validating them against multiple climate models.
The study found that in today’s climate — which is around 1.3°C warmer than the pre-industrial period of 1850-1900 — such a heat event would be expected once every five years. In a world without global warming, it would have occurred only once every 25 years, meaning climate change made it five times more likely. The analysis also concluded that temperatures during the event were around 1.6°C hotter due to climate change.
The researchers noted that climate models tend to underestimate the severity of such heat events, showing smaller changes in likelihood and intensity than observed data. But the “discrepancy between observations and models is smaller in this region than in other parts of the world.”
If global temperatures rise by a further 1.3°C — a level projected under current emissions trajectories — the likelihood of similar heatwaves would increase by another threefold, with such events potentially occurring every two years. “Despite Australia’s advanced warning systems, many people, particularly elderly and vulnerable populations do not recall heatwave alerts or act on them,” said the study.
One positive finding highlighted in the report was the reduced reliance on fossil fuel-based electricity during the heatwave. Solar power met around 60 per cent of peak electricity demand, with rooftop solar panels accounting for two-thirds of that total, the report said.
“One of our most striking findings is that the impact of climate change far outweighed natural climate variability — including a weak La Niña, which would normally signal cooler temperatures,” said Ben Clarke, a researcher at the Imperial College London and one of the study’s authors.
“The 1.6°C of heat added by emissions turned a difficult week into a dangerous one. We are seeing the limits of human and ecological endurance being tested in real-time,” said Sarah Perkins-Kirkpatrick, professor of climate science, Fenner School of Environment and Society at the Australian National University.
As these events shift from being once-in-25-year anomalies to regular occurrences, our window to adapt is closing, she added. “This is no longer a distant future threat — it is the reality of our climate today.”