Obama's climate guru: Paint your roof white!

Some people believe that nuclear power is the answer to climate change, others have proposed green technologies such as wind or solar power, but Barack Obama's top man on global warming has suggested something far simpler – painting your roof white.

Steven Chu, the US Secretary of Energy and a Nobel prize-winning scientist, said yesterday that making roofs and pavements white or light-coloured would help to reduce global warming by both conserving energy and reflecting sunlight back into space. It would, he said, be the equivalent of taking all the cars in the world off the road for 11 years.

Speaking in London prior to a meeting of some of the world's best minds on how to combat climate change, Dr Chu said the simple act of painting roofs white could have a dramatic impact on the amount of energy used to keep buildings comfortable, as well as directly offsetting global warming by increasing the reflectivity of the Earth.

"If that building is air-conditioned, it's going to be a lot cooler, it can use 10 or 15 per cent less electricity," he said. "You also do something in that you change the albedo of the Earth – you make it more reflective. So the sunlight comes down and it actually goes back up – there is no greenhouse effect," Dr Chu said.

When sunlight is reflected off a white or light-coloured surface much of that light will pass through the atmosphere and back into space, unlike the infrared radiation emitted from the Earth's warmed-up surface, which is blocked by greenhouse gases and causes global warming. "What we're doing is that, as we put in more greenhouse gases, we're putting in more insulation for infrared light. So if you make white roofs and the sunlight comes in, it goes right through that [insulation]," said Dr Chu.

The principle could also be extended to cars where white or "cool colours" designed to reflect light and radiation could make vehicles more energy efficient in summer. "If all vehicles were light-coloured, there could be considerable savings because then you can downsize the air conditioning... and downsizing the air conditioner means more efficient air conditioning and a considerable reduction in energy," he said.

Asked about whether the US administration has any plans to manipulate the climate artificially using large-scale geoengineering programmes, Dr Chu said there were no such plans "at this time". But painting surfaces white is one geoengineering proposal that he is taking seriously.

"Now you smile, but if you look at all the buildings and make all the roofs white, and if you make the pavement a more concrete-type of colour than a black-type of colour, and you do this uniformly... It's the equivalent of reducing the carbon emissions due to all the cars in the world by 11 years," he said.

"It's like you've just taken them off the road for 11 years. It's actually geoengineering."

The idea would even work in countries with temperate climates, such as Britain, because white-coloured roofs would help to reflect the radiated heat from homes and offices back into the building during winter months, said Dr Chu. One unresolved issue concerns the aesthetic considerations of making sloping roofs white. But with flat roofs that are not visible from the street, there should be no objection to painting them white, he said

Dr Chu is one of 20 Nobel prize-winning scientists attending a meeting on climate change at the Royal Society and St James's Palace organised by Cambridge University. He said energy efficiency will be the most immediate way of reducing emissions of greenhouse gases.

The white revolution: How it would work

* The idea of painting surfaces white to conserve energy is being actively pursued by the US. Earlier this month, Barack Obama's chief scientific adviser, John Holdren, received a scientific memorandum on the subject.

* Scientists estimate that making roofs and pavements white or more light-coloured would counter global warming with "negative radiative forcing" – reflecting sunlight back into space. They said that retrofitting urban roofs and pavements in tropical and temperate regions with solar-reflective materials would offset about 44 billion tonnes of carbon dioxide.

* The scientists said it would lower the cost of air conditioning, making buildings more comfortable and mitigate the "urban heat island" effect caused by the concentration of concrete surfaces in cities.