Climate change could make cities 7C warmer, say scientists

Cities will be hit the hardest by climate change because of the "urban heat island" effect that traps warmth, according to a new study.

The research, published in the journal Nature Climate Change, found that world cities will potentially face costs twice as big compared to their surroundings.

They say this is due to the "urban heat island" effect, where cities are often several degrees warmer than rural areas due to the heat trapped by dark-coloured roads and buildings.

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The phenomenon is so pronounced that it "enables olives to be grown next to a south-facing stone wall as far north as Aberdeen," The Independent reports.

Through temperature data dating back to 1950 for 1,692 cities, the researchers predicted that one in four of the world's biggest cities might be up to 7C warmer by the end of this century.

Such a steep increase would have "dire consequences for the health of city-dwellers, rob companies and industries of able workers, and put pressure on already strained natural resources such as water," says The Guardian.

The study predicts that the worst-affected cities could lose as much as 10.9 per cent of their GDP.

Cities cover only one per cent of the earth's surface, but are home to 54 per cent of the world's population.

However, the paper's authors say that the unique environmental factors of urban landscapes are often overlooked in climate change research.

"Studies on climate change impacts in cities mostly focus on a limited set of countries and risks, for example sea-level rise, health and water resources," the paper says, and "do not take into account that large cities will experience additional warming due to the urban heat island effect."

Professor Richard Tol of Sussex University says the team's findings highlight the need for locally-tailored responses to climate change.

"Any hard-won victories over climate change on a global scale could be wiped out by the effects of uncontrolled urban heat islands," he says.

"City-level adaptation strategies to limit local warming have important economic net benefits for almost all cities around the world."

The paper suggests modifications to urban construction to minimise heat absorption, including using "cooler" alternatives to asphalt for pavements, painting roofs with a reflective coating and planting more trees.