White rooftops ‘could cool the world efficiently’

It could be time to get the white paint out – as an American energy efficiency pioneer believes white rooftops could cool the world efficiently. Arthur H Rosenfeld, physicist and […]

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By Vicky Ellis

It could be time to get the white paint out – as an American energy efficiency pioneer believes white rooftops could cool the world efficiently.

Arthur H Rosenfeld, physicist and former Commissioner of the California Energy Commission has suggested that on a clear day, a white roof is only 5°C to 10°C warmer than the ambient air.

In contrast, a conventional dark roof can get 40°C to 50°C hotter than the outside air, he explained.

Writing in the International Energy Agency’s journal, the US scientist said: “My latest obsession is a campaign for white roofs in climates where summers are uncomfortably hot. White roofs not only reduce energy bills and dampen the urban heat island effect, but they also cool the world.”

He said that a cooler roof means the space beneath the roof needs less electricity for air conditioning, saving money and avoiding emissions of CO2 and other pollutants at the power plant.

Secondly, he went on, by reflecting more of the sun’s energy back into space, white roofs “cancel a small percentage of the heating effect from CO2 that has already been emitted”: “This is called the “albedo effect”, based on the Latin word for whiteness. As reflective arctic ice recedes rapidly, we need all the albedo we can get.”

Dr Rosenfeld argued that every 100 square metres of roof area that is white instead of black cancels the warming effect of 10 tonnes of CO2 over the roof’s lifetime (typically 20 years). The cumulative effect of converting most flat roofs in warm cities to white would cancel more than one gigatonne of carbon every – as much as taking half the world’s cars off the road for 20 years, he explained.