'Heat island' effect could double cost of climate change in major cities

Climate change could cost the world's major cities twice as much as the rest of the planet because of the extra heat created by the urban jungle, researchers have warned.

The "urban heat island" effect is caused by replacing plants and other natural features with heat-trapping concrete and asphalt and by the impact of heat from sources such as cars and air conditioning units.

It could add around 2C to temperature rises caused by global warming in the world's most populated cities by 2050, with economic impacts of hotter conditions ranging from more energy use for air conditioning to health risks and less productive workers.

Analysis by a team of economists of 1,692 of the world's major cities shows the total economic costs of climate change for the urban areas could be 2.6 times higher when heat island effects are taken into account than when they are not.

Losses could reach 10.9% of economic output for the worst-affected cities by the end of the century, compared with a global average of 5.6%, the analysis published in the journal Nature Climate Change found.

But local efforts to reduce temperatures, such as switching to "cool" pavements and roofs which reflect the sun and absorb less heat, could have significant benefits for cities.

Changing a fifth of a city's roofs and half its pavements to "cool" versions, which are lighter or more reflective than traditional ones, could reduce air temperatures by 0.8C and deliver savings worth up to 12 times what they cost to install and maintain.

Implementing measures at a larger scale could produce even bigger benefits, but would cost significantly more, a cost-benefit analysis by the researchers from the University of Sussex, Universidad Nacional Autonoma Mexico and Vrije University Amsterdam found.

They also found the positive impacts of local measures such as implementing cool pavements are amplified when global efforts to cut greenhouse gas emissions and curb temperature rises are also having an effect.

Professor Richard Tol, from the University of Sussex, said: "Any hard-won victories over climate change on a global scale could be wiped out by the effects of uncontrolled urban heat islands.

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

"The largest benefits for reducing the impacts of climate change are attained when both global and local measures are implemented together."