Buckled train tracks, grounded planes, melting bitumen and massive blackouts: the dystopian vision of the 50-degree city is closer to reality every day.

With wildfires raging around the Arctic Circle, unprecedented heatwaves in the Northern Hemisphere and record temperatures being set from Algeria to Canada, the world is getting inexorably hotter.

And the combination of rising global temperatures with increasing urban density is proving deadly.

Now, 50 degrees Celsius, once only associated with places like California's Death Valley or the desert wilderness of Oman and Iraq, is an increasingly frequent occurrence.

A recent study, led by Australian National University climate scientist Dr Sophie Lewis, speculated that 50C days could occur in Sydney and Melbourne within the next few decades.

Heading into 'unknown territory'

So, what happens to urban populations when our cities get halfway to boiling? Are they equipped for the impeding heat or are we heading toward urban catastrophe?

Sorry, this audio has expired Coping with the 50-degree city

It's an urgent question as we enter "unknown territory", according to Marco Amati from RMIT University.

"One image that stuck out for me was, toward the end of the Millennium drought, the picture of railway workers, in Melbourne, spraying railway tracks to try to keep them cool because they were bending out of shape from the heat," Professor Amati said.

"We have a number of systems within cities that we rely on — things like air conditioning, transport, even the asphalt is changed by extreme heat — and we don't actually know how we can cope with that in large cities.

"The way we are building cities, as higher density, highly engineered areas — you have to wonder at what point are we going to exceed those engineering constraints?"

That question is now a matter of life and death as heatwaves become increasingly common.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 2 minutes 51 seconds 2 m 51 s Heatwaves in Australia explained ( ABC Weather )

Associate Professor Camilo Mora, from the University of Hawaii, says the threshold at which heat becomes deadly can vary, but a growing percentage of the world's population is now exposed to conditions exceeding that limit.

"Extreme heat is an abnormal condition for the body," he says.

"We have an optimum temperature that is around 37 degrees so every time that it's hot the body wants to activate mechanisms to cool down."

One of those mechanisms, he says, sends blood to the skin so that through the process of sweat evaporation, the blood can cool down.

"When hot conditions last for too long you deprive certain organs of blood, specifically the gut and the lining of the gut breaks... [causing] a condition called blood poisoning," he says.

"The cells start attacking these particles inside your body, creating coagulations that eventually clog the kidneys and parts of the lungs."

Health, infrastructure and economic consequences

Professor Mora says his research shows that by the end of the century over half the world's population will be exposed to this kind of deadly heat for at least 20 days a year.

In July this year a heatwave that swept across Quebec in Canada killed over 90 people in just over a week.

A devastating mortality rate, according to Professor Mora, that pales in comparison to the more than 60,000 heat-related deaths during Europe's 2003 heatwave.

But, he says, the health impact is only one of many consequences including crippling infrastructure and economic paralysis.

"We see not only damage to the railroads but concrete also cracks so then you have roads that need to be fixed," he says.

"In some places the wires start melting because it just gets too hot at the moment when everybody is turning on their air conditioners — as a result they touch each other and create these massive blackouts.

"In the US, for example, in any temperature that is above 110F, planes cannot fly because ... the density of the air is not sufficient for these planes to take off."

Adapting our cities to these new extremes is a costly exercise, particularly in places like Europe with very old infrastructure, Professor Amati believes.

"But even then when you retrofit a warmer climate, the air conditioning that they use in places like Dubai and Abu Dhabi is different to the air conditioning that [we] use in Australia," he says.

"They use different coolants in those places to adapt to those circumstances; but it still becomes an issue of cost, of retrofitting those areas and it is still a very practical issue."

Train tracks can buckle when they expand in severe heat. ( ABC TV )

The effects of severe weather of course are not evenly distributed; developing countries are particularly vulnerable to rising temperatures.

Studies have shown that race and class are key factors in susceptibility to the worst effects of climate change, from the proximity to green spaces to exposure to air pollution.

But even in developed nations, extreme heat reveals in the starkest terms some of our cities' deep inequalities.

Wealthy nations, Professor Mora says, are far from immune.

"For instance, in Miami right now, to deal with the ... sea level rise that is damaging the roads they have to invest [billions of] dollars," he says.

"[That] money that could have gone towards education or health now has to be spent on raising the levels of the highways.

"The same goes for electricity; I know that places in Australia are dealing with a high demand of electricity during these heatwaves because everyone turns on their air conditioning, so now you have to make massive investments in improving the electrical grids."

Paint the houses' roofs white

Mitigating against the worst effects of urban heat, however, does not always need to be costly or involve massive infrastructure investments, Professor Amati says.

"In Ahmedabad, in India, they have a wonderful program to simply paint the roofs of informal houses white; there's no engineering required, there's no air conditioning required," he says.

Likewise, greening cities is crucial in limiting harm from heat exposure.

"Places like New York, for example, are putting a lot of money into the restoration of gardens," Professor Mora says.

So there are other environmental solutions that are good not only to reduce the heat but also help to mitigate greenhouse gases as well."

The question of whether we are equipped to cope or not is a matter of planning as much as anything else, according to Professor Amati.

"I think it's really a question more ... about the building regulations and about the way in which we array our suburbs and the density we live at," he says.

"But [it's] also the timing and the way we do things. We might have to adapt our work/life schedules more towards taking siestas in the afternoon, for example.

"As it is, at the moment, a heatwave strikes, everyone downs tools — people don't go to work and there's a kind of a catastrophe.

"I wonder whether we shouldn't be adapting the way we work to fit this new reality better."

'It's going to be a nightmare'

But Professor Mora warns against adaptation as a substitute for real action on climate change.

"Let's try to prevent those heatwaves from happening in the first place rather than trying to live with those things," he says.

"It's going to be a nightmare. Every single summer we are going to be paralysed because these heatwaves can pose a danger to us.

"[But] it's not too late for us to fix this problem."

Dr Lewis agrees that despite the dire outlook, the nightmare is not yet inevitable.

"We found that there are huge benefits to limiting global warming for reducing the severity of future extremes in Australia," she says.

"We are currently on track to exceed 3 degrees of global warming, which would correspond to even more severe extremes.

"That means we have to be acting now to reduce this possibility and to prepare cities for high magnitude future extremes."