Welcome to summer. Over the next few months, we'll endure heatwaves in different parts of the country. Extreme heat can be life-threatening for some people — and not necessarily the ones you expect.
Loading...It's 11pm on the first day of a heatwave in Adelaide and Kim can't sleep.
The temperature in her bedroom is 26 degrees Celsius and the air is still so she feels uncomfortable.
As she tosses and turns, her core temperature rises by 0.2C and her skin warms so she starts to sweat.
When she does manage to get some shut eye, it's poor quality.
Her sleep cycle is disrupted and she spends less time in slow wave and rapid eye movement (REM) sleep.
And there's no relief in sight.
The Bureau of Meteorology has issued a heatwave warning because the average temperatures during both the day and the night for the next few days will be unusually hot.
Loading...A few days later, Harry is starting his shift at 7am in Brisbane.
It's set to reach 35C and the humidity is already oppressive.
Harry is a 30-year-old construction worker who often operates heavy machinery.
He doesn't have a lot of access to shade and wears thick protective workwear but he's fit, so he thinks he can handle it.
Within a couple of hours, Harry's drenched in sweat but he doesn't realise the humidity is stopping the sweat from evaporating and cooling his body.
His legs start to cramp, but he puts it down to last night's gym workout.
Loading...Further south in Western Sydney, Margaret is hesitant to turn on the air-conditioning in her flat because money's tight.
The 75-year-old lives alone on the top floor of an old complex with poor roof insulation and her unit is poorly ventilated.
Today is set to reach 40C but the urban heat island effect means the temperature in her area could be 4 to 10 degrees hotter.
Margaret doesn't leave her flat very often because she can't walk very far.
She occasionally gets a lift to the shopping centre with a friend to enjoy the air-conditioning but today she's battling the heat at home.
The worst is yet to come
Heat isn't just unpleasant, it can be downright dangerous and everyone is at risk, even if you don't think you're particularly vulnerable.
When heatwave warnings are issued by the Bureau of Meteorology, it's not simply based on reaching a certain temperature, like 40C.
The average daily temperate over a three-day period (which includes both the day and the night time) must be unusually hot for the location and the time of year.
The bureau also considers how those temperatures compare to conditions over the last 30 days in the area.
2023 is the world's hottest year on record, and the odds are stacked for 2024 to be even worse.
But the climate crisis is also a health crisis.
Over the past decade, heat has killed close to 300 people and hospitalised more than 7,000, but experts believe these numbers are underestimated.
Heatwaves are already Australia's deadliest natural hazard, and by 2050, researchers predict heat-related deaths will increase almost fivefold, globally.
"The worst is coming and we need to prepare for it … there is a fundamental limit to the body's coping ability; it's a fixed goalpost," says Steven Sherwood, a professor of atmospheric sciences at the University of NSW.
So how does heat kill? And to what extent can the body adapt?
Let's check back in with Kim, Harry and Margaret.
Kim
It's day three of the heatwave in Adelaide and Kim's at a cricket game for her nine-year-old son Kai.
Temps haven't dropped below 26C for the past three nights, so neither of them have had much sleep.
Today the mercury is set to hit 39C in the shade.
But there's no shelter for spectators so both Kim and Kai will be exposed to temperatures closer to 53C.
Kim feels nauseous and doesn't feel like eating because of the heat.
She's also worried about Kai who hasn't had any breaks from play and looks like he's struggling on the field.
Kim forces herself to drink lots of water but it doesn't stop her body from overheating — her core temperature is getting close to 40 degrees and her pulse is racing.
She thought she could push through, but she's now suffering from heat exhaustion.
Harry
On day two of the east coast heatwave, Harry's feeling a bit under the weather.
He hasn't really had enough rest since finishing yesterday and had a few too many beers last night so he's starting the day dehydrated.
He's trying to rush through his shift to get home and relax, but his brain feels foggy and his concentration starts to wane.
A workmate notices Harry is pushing himself and tells him to take it easy.
"You can't use the excavator if you're not fully with it mate."
Near the end of his shift his breathing becomes rapid and shallow and he collapses. Harry is showing the early signs of exertional heat stroke, which is a serious medical emergency.
His workmates call an ambulance and while they wait they lay him in the shade, take off his shirt and douse him in water.
This rapid treatment likely saves his life.
Margaret
Margaret is home alone again today — her family members are away so can't check on her.
As she's gotten older, Margaret's sweat glands have stopped functioning like they used to, so she's finding it harder to cool down.
On top of that, she has undiagnosed heart disease, which increases her risk of a heart attack.
Margaret decides to bite the bullet and turn the air-conditioning on for a while to get some relief.
But not 30 minutes later the electricity grid gives in due to the enormous demand for power from people blasting their air-conditioners.
Due to Margaret's age, pre-existing health conditions and social isolation, this heatwave could be life threatening.
Heat exhaustion doesn't usually become an emergency if you can cool down within 30 minutes, but if you are unable to do that, it can be a killer.
Why heat kills
When your core temperature gets to about 41C your body essentially starts to cook from the inside.
To protect itself, your body tries to keep warm blood away from your internal organs and redirects it to your skin.
And your sweat glands release water and salts, which evaporate to cool your body down.
But cooling the engine room comes at a cost.
As you redirect blood to your skin there's less blood (and therefore less oxygen) flowing to your gut.
This can cause your intestines to leak toxins into your blood — a condition known as "leaky gut" — which can lead to multi-organ failure, blood clotting and death.
This is what happens when someone has "classic" heat stroke.
Another way heat can kill is by overworking your heart.
As blood is diverted to your skin, your heart has to pump harder to maintain blood pressure.
This could put you at risk of having a heart attack, especially if you have an underlying condition like heart disease, says Ollie Jay, director of the Heat and Health Research Incubator at the University of Sydney.
"Often people with these problems haven't been diagnosed and then they get over-exposed to heat and then boom, it happens."
Re-routing blood to the skin can also be a problem for your kidneys.
As less blood flows to your kidneys, your risk of going into renal failure increases. The risk is even worse when you're dehydrated.
In hot areas of Central America and South-East Asia there's an epidemic of kidney disease among agricultural workers who endure hot temperatures day in, day out, with few breaks.
Even small increases in temperature for short periods of time can also affect our brain and mood.
Heat can disturb communication between nerve cells which can lead to irritability or impaired judgement.
It can exacerbate psychiatric conditions like bipolar disorder and depression, and has been linked with increased rates of suicide.
Risks beyond the temperature gauge
Temperature is one of the main contributors to heat stress but it doesn't stop there.
"The environmental factors that impact how hot you get are dependent on temperature, humidity, wind, and the amount of solar radiation that's in the environment. And it also matters what you're doing and what you are wearing," Professor Jay says.
Humid days can be particularly dangerous, adds University of New South Wales climate scientist Sarah Perkins-Kirkpatrick.
"If it's hot and humid, your body cannot cope," Dr Perkins-Kirkpatrick says.
Sweating becomes ineffective as a cooling technique when the air is saturated, because it can't evaporate from your skin.
This is also why the "feels like" temperature is so much higher on a humid day.
Wind, on the other hand, can make you feel cooler, Professor Jay says.
That's not to say dry heat doesn't carry dangers. In those climates, the risk is how much you can sweat in the first place.
The limits of human survivability
Humans are remarkably well adapted to survive the heat.
Research has shown our body can learn to better cope with heat in a matter of weeks (up to a point), if it's sufficiently exposed to high levels of repeated heat stress, through physiological changes like producing more sweat.
Though trying to replicate this in everyday life may not be as effective, says Professor Jay, because of air-conditioning and variable weather.
There is also evidence to suggest deaths from heatwaves increase when the average heatwave temperature is more than 7C hotter than the average temperatures in that location over the past month.
Western Sydney University health economist Thomas Longden, who was an author of the study, said this may explain why heatwaves can be more deadly in milder climates, like Melbourne or even Montreal, which have had deadly heatwaves in the past.
"That could either be the body's response to that shock of heat, or also our behaviour and our lack of adaptation during those heatwave events," he says.
But even with acclimatisation, good health and hydration, researchers say there comes a point where the body simply cannot survive.
And understanding this limit is becoming more important in a warming climate with a growing and ageing population.
To describe this, researchers often use what's known as the "wet-bulb temperature" — the figure that would be read by a thermometer when it's covered in a water soaked cloth. This mirrors the way sweat can cool the body.
For years, a 35C wet-bulb temperature has been thought of as the theoretical upper limit, but researchers are starting to understand that's not always the case when you factor in more realistic human physiology.
In some scenarios — particularly hot, dry environments — new research has found the wet-bulb temperature limit is much lower.
The 35C limit is what the thermometer would read at 100 per cent humidity, but it doesn't have to be that exact combination.
For example, a higher temperature but with lower humidity, such as 43C with 60 per cent humidity, would be the equivalent.
Hitting the limits
These kinds of conditions occur only very rarely today in coastal areas of the Middle East and for very short periods.
But they will gradually spread as warming continues, and Australia is not immune, according to Dr Perkins-Kirkpatrick.
"It's only going to get worse," she says.
Hot days, hot nights and heatwaves are some of the most obvious and direct effects of climate change.
Even the La Niña years of today are hotter than the El Niño years of 50 years ago.
Dr Perkins-Kirkpatrick says central and northern Australia will experience the harshest temperatures, but that doesn't mean southern areas are off the hook.
She says those areas will still reach temperatures never experienced before.
"So while it might not be that it's unsurvivable, we will certainly have to change how we currently live and work to cope with those conditions, because we don't currently know what to do in those types of scenarios," she says.
Margaret, Harry and Kim had close calls. Here's how they got through and changes they've put in place to help them cope with the next — because there will be a next — heatwave.
Learning to live with the heat
Margaret's neighbour knew she lived alone and decided to check in on her.
They came over and took her to a community centre in another suburb where there was air-conditioning.
On the next hot day in Sydney, Margaret decides to use a fan early in the day.
Loading...Margaret sets her air-conditioner to 27C and turns the air-con on when the room reaches the same temperature.
The fan will increase the airflow across her skin keeping her cool even though the air-conditioner is set at a higher temperature.
This strategy will make the air temperature feel about 4C cooler, and is also whole lot cheaper and more energy efficient than having the air-con set at a lower temperature — as long as the power is working.
"It works really well, in fact it reduces electricity consumption from air-conditioners by 70 per cent," Professor Jay says.
Loading...Harry spent two days in hospital so doctors could monitor him for complications.
He was told to avoid physical activity for a week and that a complete recovery could take months.
On his return to work his supervisor decides to implement work/rest cycles which mean workers must rest for 15 minutes every 45 minutes if performing moderate work at 37C.
Rest time is extended for every 1 degree increase in temperature or if humidity is over 40 per cent.
This will give the workers an opportunity to reduce the amount of heat their bodies are producing.
Harry decides to shop around for lighter workwear with ventilation patches on the arms and legs which will enable more sweat to evaporate.
Other parents at Kai's cricket match noticed Kim was unwell and took her to the change rooms where they poured water over her and fanned her to help that water evaporate.
The following week Kim decides to speak to the head of her son's cricket team about an extreme heat policy.
While the overall risk of heat stress in cricket is lower than other sports (given there’s less running and jumping) a cricket match lasts far longer.
While not possible to pick a specific temperature to suspend play (as humidity, cloud cover and wind speed all play their part) other measures can be taken.
Loading...She suggests the club consult an online tool which calculates the heat risk of participating in a certain sport by assessing your location, the time and weather.
The cricket club agrees to schedule matches earlier in the day and buy shade sails and misting fans for the spectator area.
Kim thought drinking as much water as possible was her best bet, but the power of evaporation means misting fans will do a far better job at reducing the heat load on the body.
It’s a matter of life and death that people know how to cool themselves down as the planet keeps warming.
But the best cooling strategies are the ones that people can actually adopt.
"The most vulnerable can't afford the latest ice vest or the latest gadget," Professor Jay says.
"We've got to think about things people can do right now with the resources they have."
Credits:
- Reporting: health reporter Paige Cockburn and weather reporter Tyne Logan
- Illustrations: Emma Machan
- Editing: Genelle Weule, EP ABC Science digital, Edwina Farley, national editor, climate and regional team
- Commissioning editor ABC News: Danielle Cronin
With thanks to Professor Ollie Jay (University of Sydney) and Dr Jason Lee Kai Wei (National University of Singapore) who guided the evidence-based scenarios on which the story is based.