It's no surprise that cities tend to be warmer than their surrounding areas. They're full of heat-producing organisms and machines; they're often built from dark materials; their hard surfaces retain heat. The phenomenon even has its own name: the "urban heat island" effect.
During cold winters, this can helpfully keep temperatures a little higher and prevent snow and ice from sticking to streets. But in summer, it's a different story: temperatures in cities (especially in naturally hot countries) can climb painfully high.
In Australia, no stranger to heatwaves, a campaign was launched this year to tackle the urban heat island effect. The country’s science agency (CSIRO) found that doubling the number of shady trees to create “green umbrellas” in cities could cut heat wave-related deaths in the elderly by up to 30 per cent. This is partly because the shade prevents direct sunlight from reaching those in public spaces; and partly because greenery has a natural cooling effect. According to the United States Environmental Protection Agency, introducing trees and vegetation can reduce peak summer temperatures by 1- 5°C.
Based on this research, the 202020 Vision campaign is hoping to increase urban green space by 20 per cent by the year 2020. They’ve launched 123 projects so far across Australia’s cities, most of which involve planting trees and vegetation on unused land and rooftops.
Sheryn Pitman, project officer for the Botanic Gardens of South Australia and host of the first leg of the 202020 campaign's nationwide tour, told The Australian that city living (apartments, no gardens) is partly to blame for rising temperatures:
"If we're losing our back yards through the ways cities are changing, then we have got to concentrate on our public spaces, streets, parks."
The campaign group also analysed the existing tree canopy cover across Australia’s cities. In some, like Hobart and Brisbane, at least half the city was covered by green canopies. In Southern cities like Adelaide, Sydney and Melbourne, however, it was 20 per cent or lower. Looks like they've got some work to do.