Painting roofs white is as green as taking cars off the roads for 50 years, says study

Painting roofs white and using light-coloured materials to surface roads and pavements would not only make cities cooler in summer, it would save the same amount of carbon as taking all the cars in the world off the roads for 50 years, a study has found.

One of the simplest, yet most effective, ways of engineering the urban environment to cope with global warming is to increase the reflectivity of the cityscape so that more of the incoming sunlight is directed back into space, scientists said.

City buildings in warm climates with "cool coloured" surfaces that reflect infra-red radiation would also be cooler than traditional buildings and so would conserve energy – and carbon – that would otherwise be used on air conditioning.

Increasing solar reflectance or "albedo" has been suggested as a way of combating the "heat island" effect of towns and cities, where summers are made unbearably hotter in built-up areas by Tarmac roads and dark buildings that absorb sunlight.

Two years ago, Barack Obama's top man on global warming, Professor Steven Chu, the US Secretary of Energy, suggested at the Royal Society in London that one of the most effective engineering measures to tackle rising temperatures is to paint roofs.

"If the building is air-conditioned, it's going to be a lot cooler, it can use 10 or 15 per cent less electricity... you also do something in that you change the albedo of the Earth – you make it more reflective," Professor Chu said. Now scientists, led by Professor Hashem Akberi, of Concordia University in Canada, have studied this in detail and found that it can have a significant impact.

They estimate that a city or town where the roofs and the pavements and roads have light-coloured surfaces can increase their albedo by about 10 per cent, which globally would provide a CO2 offset of between 130 billion and 150 billion tonnes – the same as taking every car in the world off the road for 50 years.

"Increased albedo can decrease atmospheric temperature and counter some of the anticipated temperature increases from global warming," the scientists say in the journal Environmental Research Letters.

Albedo is measured on a scale of zero to one, where 1.0 is totally reflective and zero absorbs all sunlight.

The researchers believe that it would be cheap and easy to increase the albedo of cities by applying the reflective materials when roofs and roads are routinely resurfaced, rather than doing it as a special measure.