Australia Weather News

As Australians prepare to swelter through a hot El Niño summer, the risk of heat stress also rises.

When we age, our bodies are no longer able to cope with heat as well as they once did.

We sweat less, making it tougher to cool down; our hearts do not pump blood as efficiently and we are more likely to have chronic health conditions — such as diabetes — which make it harder to handle hot weather.

But according to a new study, published today in The Lancet Planetary Health, the impacts of heatwaves on people over the age of 60 have been underestimated.

US researchers found people above this age faced serious health risks from heat at much lower temperatures than previously understood.

The study's lead author, Qinqin Kong from Stanford University in California, said it was important to understand how older people tolerated heat in different locations as the world was getting hotter and people were living longer.

The global study found the biggest future risk was in tropical and subtropical regions, but Australia's hottest regions, such as the Top End and Kimberley, were also of concern.

Dr Kong's team looked at the heat limits in three specific age groups — young adults, middle-aged people and older adults — and plotted around the world how well each demographic would cope over a year in different climate warming scenarios. Scenarios ranged from 1.5 to 4 degrees Celsius warmer than pre-industrial levels.

Most previous studies, Dr Kong said, applied the heat limits for healthy young adults to all age groups, which overlooked the "vulnerability" of older people and underestimated future health risks.

After accounting for age, Dr Kong said the picture of future heat risk "changed dramatically".

Dr Kong said his team's modelling suggested uncompensable heat — where the body could not cool itself down, no matter how fit or acclimatised someone was — would be "much more widespread, frequent, and imminent than previously estimated".

"One of our most striking findings is that older adults face more frequent and widespread uncompensable heat at just 1.5C of global warming than young adults do even at 4C," he said.

More older people at risk in warmer world

As each person copes with temperature differently, there is no clear safe level of exposure to uncompensable heat.

But laboratory experiments show a young adult's core temperature can reach heat stroke level after 3–10 hours exposure to such conditions.

Dr Kong said the temperature at which people aged 60 and older could "no longer maintain a stable core temperature" was roughly 4.7–7.5C lower than for young adults.

"Depending on the level of global warming, we estimate that the number of people facing at least 180 hours of uncompensable heat each year is about two to eight times higher than previous estimates that assumed everyone could tolerate heat as well as young adults," he said.

According to the study's projections, at 1.5C of warming, 22 per cent of people over 60 across the world, about 290 million people, would swelter through unsafe heat for at least one month a year.

Young adults would not be exposed to similar risk until about 4C of warming. The world is currently on track to reach 2.8C of warming over this century, according to the United Nations' environment program.

Dr Kong said the study showed a person's age appeared to matter "as much or more" than temperatures caused by global warming.

Australia 'not quite prepared'

The study, which looked at the potential impacts of increased temperatures across the world, included some Australian data.

Based on the modelling, Dr Kong said projected risk was "particularly relevant" for older adults in the hotter parts of Australia.

Sarah Perkins-Kirkpatrick, a climate scientist at the Australian National University who did not contribute to the study, said this was concerning as Australia was "not quite prepared" for more extreme hot weather.

"There will be events at higher global warming levels that occur over our major cities and we are not prepared for them," she said.

"If we have one of these deadly heat stress events, in Sydney, Melbourne, or Perth, keeping people alive is going to be very tricky with our current resourcing, particularly older people."

Dr Kong added his study only measured one specific pathway through which heat became dangerous: "Pushing the body out of thermal balance and raising core temperature."

Heat does not need to push the body to heat stroke conditions to cause a person serious harm.

"It can worsen cardiovascular, kidney and respiratory diseases, particularly in older adults, and physiological strain can begin before core body temperature starts rising continuously," Dr Kong said.

Dr Kong said the findings could differ depending on heat tolerances of people living in different parts of the world.

This is because the experiments used to design the heat limits used in the study took place in the US, and people living in hot climates, such as India, could be more acclimatised to heat and able to tolerate hotter conditions.

"We tested this possibility by allowing for higher heat limits in warmer climates. This reduced our exposure estimates, but the main conclusions did not change," Dr Kong said.

Professor Perkins-Kirkpatrick said one of the study's strengths was it explored in "more granular" detail about how future predictions of warmer weather were likely to impact different age groups, which had not been done before.

"This is a pretty accurate prediction using the best modelling tools that we have," she said.

"It is a clear relationship; the more we heat the planet, the more shit is going to hit the fan."

It is a sentiment echoed by heat stress scientist Matt Brearley, who did not contribute to the study, describing its findings as a "wake-up call".

"Because of global warming, the elderly are going to be more vulnerable for longer, especially those in the tropical regions and places that are warming faster," he said.

"It's going to be much worse than we thought."

Targeted heat action plans needed

Dr Kong's team want their findings to be used in the development of age and region-specific heat action plans.

Professor Perkins-Kirkpatrick said although there was no "one silver bullet" to preparedness, from a healthcare perspective, Australia needed to make sure staff were better trained and better resourced when heatwaves and extreme weather events were forecast.

"They're pushed to their limits already during current extreme events … you have ambulance ramping, people's calls going unanswered," she said.

But Dr Brearley said there were a few practical things Australians could do to prepare themselves as they aged.

"Fitness is key to managing heat stress, and what I see with aging populations is they have much lower physical activity levels," he said.

And while he urged people not to "overdo it", for those who lived in hotter climates, he said it was important to acclimatise if you can.

But Dr Kong warned that helping people adapt to life in a hotter world, on a personal and community level, did not "eliminate the underlying problem".

"Limiting further warming through reductions in greenhouse gas emissions remains the most fundamental way to prevent these risks from continuing to grow," he said.