Half a year of dangerous heat beckons for parts of Australia in 1.8-degree warmer world

Scientists are learning what global warming will mean for daily temperatures across the world and what adaptation and mitigation will be required to protect people from dangerous heat.

Heatwaves have killed more Australians than all other natural disasters combined and projections by scientists from Harvard University in the US suggest more are on the way.

The projections, published in Communications Earth and Environment, suggest a child born in some parts of Australia today could be living through regular days of “dangerous heat” by the time they retire.

And the picture worsens the closer one moves to the equator, with the picture for the Indian subcontinent and subtropical Africa in particular facing more than 150 days of “dangerous heat” a year.

The research uses the already observed global temperature increase of over 1°C (on pre-industrial baselines) and carbon dioxide concentrations in the atmosphere, and models a future temperature increase scenario of a 1.8°C average increase in global temperatures by 2050, and 3°C by the end of the century.

The American heat index – an indicator that classifies the apparent daily temperatures as posing either “dangerous” (likely onset of heat exhaustion related symptoms at 40°C) or “extremely dangerous” (potentially leading to heat stroke and increasing risk of fatality from 51°C) – is then used to indicate how many dangerously hot days will occur around the world, based on these projections.

Too hot to handle?

Australia is accustomed to regular heatwaves – multiple summer days over 40°C is not unheard of in the south-east of the country and even higher in the inland and northwest.

It’s when the humidity spikes those temperatures become dangerous – this is what heat indices consider.

Median projections from the Harvard research suggest a city like Darwin could average between 50 and 100 ‘dangerous’ days each year by 2050, and more than a hundred by 2100.

“Particularly in places where things are already marginal like the top end of Australia. If you go from an average of 32 to 33 degrees, that also means your extremes are increasing massively.”

Associate Professor Ailie Gallant

The north-west coast of Western Australia could also see two weeks’ worth of ‘extremely dangerous’ days.

For the southern capitals that barely experienced a dangerously hot day in the past, even the five on average predicted by Harvard each year may be dangerous.

And this is a median scenario. The risk will reduce if constructive action to mitigate global warming is taken. And will get worse if not.  

Using temperature averages like those in this global study provides a starting point for climate scientists to describe future scenarios and for communities to respond.

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As Associate Professor Ailie Gallant from Monash University’s school of Earth, Atmosphere and the Environment explains, small increases in average predictions often hide jumps in temperature extremes.

It’s changes at the extremes which pull averages higher.

“The thing with climate change is that you expect shifts in what we might call the temperature distribution,” says Gallant.

“The average changes because the extremes change.

“So when we’re thinking about heat waves, about extreme heat, and we’re talking about even relatively small shifts – like two degrees – it makes a big difference at the extreme end of the spectrum.

“Particularly in places where things are already marginal like the top end of Australia. If you go from an average of 32 to 33 degrees, that also means your extremes are increasing massively.”

It’s not just the hot weather, it’s the way we respond

Heatwaves are indirect killers, working with other morbidities to bring about deaths earlier than may have been anticipated.

While not involved in the Harvard research, Professor Richard Franklin from James Cook University’s school of Public Health, Medical and Vet sciences says such predictions are similar to modelling done in Australia.

Franklin’s research looks at the health impacts of hazardous events and he recently co-authored a study reviewing the impact of heatwaves on health service demand for Queensland’s Department of Environment and Science.

“You add heat into what are already stressed people – they’ve got chronic disease or other sorts of conditions like cancer or cardiovascular disease – they’re dying and the body just can’t cope,” Franklin says.

The social implications of hot weather go beyond mortality predictions. 

Franklin points to the breakdown of infrastructure in heatwaves across the US this year as an example of what dangerous heatwaves can cause.

During this year’s American heatwaves, some cities’ public transport services couldn’t operate, ambulances were grounded by road melt, electrical grids experienced brownouts and blackouts, and homeless people passed away due to the high and inescapable heat.

However increasing heatwaves may also create a “lag” effect.

This might occur when a heatwave – defined in Australia as “three or more days in a row when both daytime and night-time temperatures are unusually high” – comes to an end, but temperatures in the days following are still enough to trigger illnesses and calls to emergency services.

This is something the James Cook University researchers found in their study.

“We know there’s excess mortality, we know there’s an excess number of calls to triple-zero, we know there’s an excess number of people that go to the emergency department and hospitals,” says Franklin.

“In our research we saw an excess number of calls to ambulance services, but what we didn’t expect to find was a lag effect.

“That’s probably due to the hot conditions continuing on, so even though you wouldn’t classify it as a heatwave, the conditions are still hotter, and because of that, we’re seeing an increase in calls and probably deaths as part of that. 

“It is quite concerning, and the load on the health system in trying to deal with it, as well as other systems, is why we doing this work.”