CENTURIES-old heatwave records have been shattered all over Australia in the past week as cities from Hobart to Sydney have been hit by prolonged stretches of temperature far above normal.

Hobart’s recent run of six consecutive November days above 26C hasn’t been equalled for 130 years.

While it may have been warm, though, it was manageable.

However, climate scientists are warning the conditions in another of Australia’s capitals could get so bad it may become “not viable” to live there in decades to come.

A combination of debilitating humidity and what’s known as the “urban heat island effect” mixed in with a good dose of climate change could leave Darwin off-limits to all but the hardiest.

Already, surface temperatures in parts of Darwin’s CBD have been recorded nudging 70C.

And regional cities in Queensland might not be far behind.

Towards the end of November, Darwin locals look forward to the end of the “build-up”, the hot and sticky weather that precedes the wet season.

It’s been a tough few months. Earlier this year, the Bureau of Meteorology warned 2017’s build-up would be “brutal”.

“Everything is hotter than normal,” said the Bureau’s Greg Browning.

Australian National University’s Dr Elizabeth Hanna, an expert on the effects of climate change on health, told news.com.au it was the Top End’s tropical humidity that was the big problem.

“We can cope with much higher temperatures in Melbourne because the air is drier, but in Darwin the high temperatures and humidity are oppressive.

“If it gets worse, those unpleasant times of the year (like the build-up) will extend longer and longer making it not a viable place to live,” she said.

UNINHABITABLE

Mattheos Santamouris, a professor of high performance architecture at the University of NSW, is working on a project, funded by the NT Government, to study how Darwin’s heat can be given the heave-ho.

“The focus is often on the global impact of climate change, but we also need to understand what is happening at a local level, in our own cities,” Prof Santamouris said.

“If we can’t find a way to make our cities cooler, they will eventually become uninhabitable.”

A cautionary tale of a possible future for Darwin lies further north. In August, there were warnings from scientists that by the turn of the century India could be hit by climate change fuelled heatwaves so extreme they could kill even healthy people within hours.

Under a scenario where carbon emissions were not throttled back, 4 per cent of India’s population would experience a non-survivable heatwave at some point after 2071.

A wet bulb temperature (which takes into account humidity) of 35C is when things start to head south.

“We need to evaporate and sweat to cool down but when temperatures get close to or above our core temperature, and when humidity is high, the air becomes saturated and we’re not going to lose that sweat so our cooling mechanism is hampered,” said Dr Hanna.

The conditions wouldn’t affect everyone equally but in a major heatwave in India, she said, people could start to overheat even when sitting still.

‘RIVER OF FIRE’

“If it’s 38C outside people feel crappy and grumpy and that has an impact on assaults so it has all manner of social issues,” she said.

In August, the Territory Government kicked off a project to see where Darwin’s hot spots were — and what was causing them — so they could cool the CBD down.

The heat mitigation study uses a dedicated “energy bus” and drones to measure surface and air temperatures.

“The study found our streets, parking lots, roofs and pavements have very high surface temperatures, ranging from 45-67C,” said Chief Minister Michael Gunner at the time.

“Areas such as the Post Office carpark, the Supreme Court car park, and the Bus Terminal are incredibly hot — Cavenagh Street (a CBD thoroughfare) is a river of fire.”

Prof Samtamouris told news.com.au Darwin was a classic case of an urban heat island where materials used in roads and buildings turbocharged temperatures.

BITUMEN

“Black surfaces like bitumen absorb high amounts of solar radiation leading to high surface temperatures.” he said.

“A material with a temperature of about 70C may heat the air by around 3C.”

Alternative materials, such as special “cool” asphalt, can bring the surrounding temperatures down.

“In Darwin, you have overheating because there’s too much bitumen and not enough greenery”.

The study will continue for the next year but the Government said it is already burying one of its major carparks to reduce its impact on air temperatures.

And it’s not just Darwin. Sydney’s west is regularly up to 10C warmer than the CBD. The reasons are different — the CBD is cooled by winds coming off the seas which peter out by the time you reach, say, Penrith.

But the result is the same — increasingly uninhabitable cities. And climate change, pushing average temperatures up, continues to stymie mitigation efforts.

“Townsville and Cairns are not as bad but they will start to become like Darwin. Everything is just moving to the extreme but we just don’t know exactly when or how fast it will happen.” said Prof Hanna.

“Global temperatures are going so badly and emissions are increasing so much that it’s not looking good.”

Planting more trees and creating shady streets was a good strategy to make cities more liveable, she said. But a few plants here and there had their limits.

“As it keeps warming and warming, there’s only a little it can do.”

benedict.brook@news.com.au | @BenedictBrook