The measures needed to cool Australia’s rapidly heating urban environments are already clear – and the case to implement them is now urgent, as global temperature records topple. By Elizabeth Farrelly.

Planting the urban jungle

Urban Forests Belgium plant a Miyawaki microforest in Brussels.
Urban Forests Belgium plant a Miyawaki microforest in Brussels.
Credit: Urban Forests Belgium

Midwinter might seem an odd time to angst about urban heat. It’s cold, kind of. Sydney, despite a series of spring-like, dolphin-leaping days, has had a few single-figure nights and in Melbourne recently, frost warnings remained until 3pm. I say enjoy it while you can. We’re racing to a future where cold will be a luxury.

In the past few weeks, global temperature records have been repeatedly toppled. Heatwaves have brought wildfires, death and destruction to Greece, Spain, Italy, India, China and the United States. In California’s Death Valley, the temperature reached 53.3 degrees – a must-visit for a new breed of so-called “heatwave” tourists. They will soon find they don’t have to travel far. This kind of heat is closer than you think, in time as well as place.

On January 4, 2020, the hottest place on Earth was Penrith, in Western Sydney. Its official temperature was 48.9 degrees, but at several locations a team led by Associate Professor Sebastian Pfautsch of Western Sydney University recorded air temperatures of more than 50 degrees. Bear in mind that, according to the Bureau of Meteorology, above 35 is defined as “hot” and above 40 “extreme”. Fifty is something else.

I’ve experienced 50-degree heat only once, on the edge of the Simpson Desert, near where Caroline Grossmueller, a fit young Viennese medical student, died in 1998. She had plenty of water and was just 35 kilometres from her hotel when she expired of heat exhaustion. It seems inconceivable – until you step out into that kind of heat. Within minutes, you feel your organs cook.

Already, says Sydney cardiologist Fiona Foo, “heatwaves are silent killers, causing more deaths than other natural disasters combined”. Australia is the world’s hottest continent. It’s also heating faster than most. As if that weren’t bad enough, we now confront another El Niño. What does it mean for our cities?

Generally, the city offers a refuge from natural cataclysms such as fire or flood. With heat, however, our cities are intensifiers. The urban heat island effect is well documented. Hard surfaces, heat-absorbent materials, relentless traffic and lack of shade can all contribute to make urban temperatures 10 or 15 degrees higher than surrounding rural areas – especially at night.

The recent refitting of Melbourne’s Collins Arch building (aka “the pantscraper”, designed by New York firm SHoP Architects with Woods Bagot), is another example of unnecessary urban heat – in this case, one that fries locals. It’s a phenomenon whose earlier manifestation, from Rafael Viñoly’s so-called “walkie-talkie” building in London, gave rise to the term “fryscraper”.

This is a significant public health risk, and it’s unevenly spread. In all our cities, fryscrapers notwithstanding, there are naturally hot areas and cooler areas. The cooler areas, tempered by the ocean’s thermal mass and rinsed by its breezes, are also typically wealthier. The inland areas, naturally hotter, are also those of social disadvantage and where many live with chronic diseases such as diabetes and cardiovascular disease, which render people more vulnerable to heat stress. So those least able to cope are often by far the most affected.

“We house them in dark-roofed uninsulated ovens and, at those temperatures, people die,” says Western Sydney GP Kim Loo.

So this isn’t just about equity – it’s about survival. With about 86 per cent of Australia’s population urbanised, the shape of our cities will condition our future, and whether we have one. What should change?

The answers divide into heat mitigation – effectively, climate adaptation – and those broader measures designed to mitigate climate change itself. The second category is more familiar, so let’s look at the first. What might a cool-city oasis look like on the ground?

The most obvious measure is shade – especially, urban tree canopy. This is so obvious it barely needs mentioning, except that our governments are conspicuously better at talking than walking. The City of Melbourne – typically a leader in things urban – has countless policy documents on the subject, as does the City of Sydney. Adelaide too. Outside their centres, though, our cities are fast-tracking forest-felling, car-dependent sprawl at an accelerating rate.

Justified now as “housing provision”, these new developer-led estates typically cram large houses onto small sites, too close together for there ever to be significant tree cover. Even where tree-planting strategies exist, such as New South Wales’s feted “one million trees” program, the trees in question are often pencil-high, decades short of any decent shade.

The shade issue – like carbon sequestration more generally – brings up an interesting conundrum over native versus introduced species. The well-shaded streets of our old city centres, lined mostly with deciduous European trees such as London planes and liquidambar, have long been reviled by native advocates. Many councils still destroy such trees on principle, including “weeds” such as camphor laurel. But all trees provide shade, hold groundwater, nurture soil and suck carbon. Deciduous trees also provide dense summer shade (and delicious winter sunlight) and offer significant fire retardancy due to their dense and sappy trunk wood. So can we afford to discriminate? Should we not treasure all trees, regardless?

Absolutely, says Sebastian Pfautsch. “That native preference is about ideology. I’m interested in function. Residential streets should have a constant canopy – and deciduous is good in winter. Plus a city is anyway synthetic…”

Surface treatment is also critical. Our roads and roofs should be pale – reflecting heat rather than absorbing it. Again, it’s such a simple measure. But when NSW’s then minister for Planning, Rob Stokes, tried to introduce it in 2021, he was unsuccessful and the dark-roofed sprawl continued. Pale roads need a little more care to ensure they don’t reflect solar glare into traffic or apartments, but a study in Sydney’s inner-city Chippendale by Michael Mobbs’ Street Coolers project suggests they can reduce temperatures by 5 degrees.

Green roofs and walls are another excellent remedy, cooling by both transpiration and insulation, while sequestering carbon and potentially providing food. In 2015, France passed a law requiring new commercial roofs to be solar or green – or, better still, both, because cooling greenery improves photovoltaic efficiency. There are also “air gardens” that, misted with nutrients, suspend a living canopy over the street – from which it is easy to imagine a world in which urban agriculture brings strawberries, lettuce or coriander to the walls and roofs of our cities.

In greening the ground plane, we clearly need to maximise the cooling, flood-mitigating effects of living botanicals. Rather than synthetic turf, which further concentrates solar heat, pollutes waterways and kills soil, we should promote real grass – on sports fields, playgrounds, streets, infrastructure and, as in Bilbao or Frankfurt, tram tracks. As our cities become denser – as they must to end sprawl – they should also become greener. This implies a proliferation of parks, both large and small, with urban agriculture. Imagine street corners with Miyawaki microforests – ultra-diverse ecosystems designed by Japanese botanist Akira Miyawaki in the 1970s that, working from complex inter-species symbiosis, can occupy just a few square metres and grow at extraordinary speed.

As to urban form, there’s no perfect shape for urban cooling. But one thing is clear: plants need light and cooling needs air, so the dense clusters of super-tall towers that characterise so much current development should give way to varied heights and shapes that maximise permeability.

So yes, global warming is a fearful spectre as Earth enters uncharted territory. But it’s also an opportunity to repurpose our cities as verdant oases in which under-street aquifers sustain countless small-footprint forests, freeways hang with vines and every street wall brushes your cheek with dewy leaves. We have the picture. Now, for a chance to escape a grim future, we need to make it real.

This article was first published in the print edition of The Saturday Paper on July 29, 2023 as "Planting the urban jungle".

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