Climate change to ‘hit big cities twice as hard’

BRITAIN: Crowded cities could be affected twice as badly as their surroundings by climate change because of the ‘‘urban heat island’’ effect that traps warmth.

One in five of the largest conurbations could be 4C warmer in 2050 than they were at the end of World War II, researchers estimate. A quarter of the world’s biggest cities may be 7C hotter by the end of this century without substantial mitigation.

The heat-island phenomenon comes about as plants and bodies of water give way to concrete and asphalt, which can absorb and conduct much more thermal energy. This can cause higher temperatures and change patterns of rainfall and wind speed.

Climate economists have calculated that this will have added 2.08C to temperatures in the world’s megacities by the middle of the century, and 0.84C to middlesized cities. By 2100 the economic cost could be 2.6 times higher with the heat-island effect taken into account, rising to 10.9 per cent of GDP, according to projections for 1692 cities published in the journal Nature Climate Change.

This means that even if global warming can be constrained by a marked reduction in carbon emissions, any gains would be wiped out in the cities that are expected to house two thirds of the world’s population by 2050.

Richard Tol, professor of economics at the University of Sussex and one of the paper’s authors, said that the onus was on authorities in urban areas to safeguard the future of their citizens.

‘‘Any hard-won victories over climate change on a global scale could be wiped out by the effects of uncontrolled urban heat islands,’’ he said. - The Times