UK: Overheated cities face climate change costs at least twice as large as the rest of the world because of the urban heat island effect, new research shows.

The study by an international team of economists of all the world’s major cities is said to be the first to quantify the combined impact of global and local climate change on urban economies.

The analysis of 1,692 cities, published in the journal Nature Climate Change, shows that the total economic costs of climate change for cities this century could be 2.6x higher when heat island effects are taken into account than when they are not. The researchers claim that costs for the most affected cities could reach 10.9% of GDP by the end of the century, compared with a global average of 5.6%.

The urban heat island occurs when natural surfaces, such as vegetation and water, are replaced by heat-trapping concrete and asphalt, and is exacerbated by heat from cars, air conditioners, etc. This effect is expected to add a further 2º to global warming estimates for the most populated cities by 2050.

The authors – from the University of Sussex, Universidad Nacional Autónoma de México and Vrije University Amsterdam – say their new research is significant because so much emphasis is placed on tackling global climate change, while they show that local interventions are as, if not more, important.

Professor Richard S J Tol MAE, professor of Economics at 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 research team carried out a cost-benefit analysis of different local policies for combating the urban heat island, such as cool pavements – designed to reflect more sunlight and absorb less heat – cool and green roofs and expanding vegetation in cities.

The cheapest measure, according to this modelling, is a moderate-scale installation of cool pavements and roofs. Changing 20% of a city’s roofs and half of its pavements to ‘cool’ forms could save up to 12x what they cost to install and maintain, and reduce air temperatures by about 0.8º, the researchers say.