Lethal warming has begun and could rapidly escalate to cause massive population displacement, prompting calls from the country’s leading strategic policy institute for the government to plan for cascading disasters around the region.
New research authored by Dr Robert Glasser, a senior fellow at the Australian Strategic Policy Institute, warns that Indonesia will be the country in our region at most risk from lethal humidity caused by the twin rise of heat and humidity, which robs people’s bodies of their main cooling mechanisms – perspiration and evaporative heat loss.
Heat stress is already a major cause of death. The federal government warns that heatwaves lead to more deaths than any other natural hazard, routinely killing hundreds of people during each event.
Children and people aged over 65 are particularly at risk.
“I wonder how many Australians realise that each year heat kills more people than all the Australians who were killed in the Vietnam War,” Glasser said.
“In fact, it’s something like five times more than all the Australians killed in the Vietnam War, each year dying from heat stress in Australia.”
In Australia, the Northern Territory is most at risk of accelerating lethal humidity conditions as global temperatures rise. But our region’s ground zero is Indonesia, where humidity is already high in the wet and the dry seasons.
“It’s really remarkable what an overlapping centre of climate hazards Indonesia is,” Glasser said. “It also has the fastest sea level rise in the world, it has the largest exposure to a range of natural hazards – many of which climate is amplifying. Indonesia, on our doorstep, is at huge risk from these issues.”
Australian policymakers should start preparing for the risks to hit our region as temperatures and humidity rise, Glasser warned.
“It’s entirely possible, maybe likely, that the impacts in our region that affect us directly will be greater, whether it’s people movements from communities that are displaced by these disasters, or whether it involves food insecurity.”
When humidity is combined with high temperatures, stripping the body of the ability to cool through perspiration because air is already saturated with moisture, the body responds by redirecting blood flow from internal organs to the skin, to offload internal heat.
A cascading series of processes can lead to mass coagulation, organ failure and death.
A 2010 study in the peer-reviewed PNAS science journal suggested a human could not survive for more than six hours at a “wet bulb temperature” – the reading when a wet cloth is over the bulb of a thermometer – of 35 degrees.
If temperatures are 40 degrees and relative humidity is 50 per cent, the wet bulb temperature is 31 degrees. At 40 degrees with 75 per cent humidity, it is about 36 degrees.
On average, Glasser found, South-East Asia and the Indo-Gangetic Basin, which takes in northern India and parts of Pakistan, Nepal and Bangladesh, now experience three or more months a year of wet bulb temperatures exceeding 27 degrees.
His report, titled Lethal humidity and the systemic risks of climate change, warns that each new decade in which temperatures rise will expose many tens of millions more people to deadly humid-heat extremes.
“As much as 50-75 per cent of the global population will be exposed by late this century,” the report finds. “That dire trajectory elevates lethal humidity from a high-impact risk to a systemic global threat, requiring rapid reductions in greenhouse gas emissions and decisive policy responses.”
Glasser said the upper limit of humid-heat tolerance in older adults is significantly lower – about 23 degrees to 28 degrees – than in younger individuals.
“Climate change is still often regarded as solely an environmental issue – and is generally co-ordinated in governments by environment ministries – rather than as a systemic crisis that affects every aspect of society.”
Billionaire Andrew Forrest, whose Minderoo Foundation provided funding for the report, described it as a groundbreaking wake-up call for policymakers.
“High humidity doesn’t just make heat more uncomfortable. It pushes entire regions past the limits of human survival,” he said.
“We are not prepared for cascades like that at scale – cascades that lead to stampede migration and mass mortality. The window to stop lethal humidity becoming a defining reality for billions of people, not just in Australia but across South-East Asia, is rapidly narrowing.”
Glasser previously served as the United Nations secretary-general’s special representative for disaster risk reduction, and as secretary-general for aid organisation Care International.
He called for urgent research into how livability will be diminished as lethal humidity thresholds are approached, an expansion of focus and research into less-developed countries, and the prioritisation of adaptation planning for tropical coastal cities and countries most at risk.
“This isn’t a threat that we can isolate ourselves from … we can reduce the risks in Australia, but the risks outside are really big and growing fast,” he said.
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Bianca Hall is The Age’s environment and climate reporter, and has worked in a range of roles including as a senior writer, city editor, and in the federal politics bureau in Canberra.Connect via X, Facebook or email.