A leading energy efficiency expert has called for roofs in cities with uncomfortably high summer temperatures to be painted white.
Arthur Rosenfeld of the Lawrence Berkeley National Laboratory in California and former advisor to the US Department of Energy, claims that every 100 square metres of black roofing painted white, could save 10 tonnes of CO2 during its lifetime.
White roofs reflect more energy from the sun back into the atmosphere. Black roofs absorb the energy which also means more air conditioning is needed, which increases CO2 output.
“On a clear day, a conventional dark roof can get 40°C to 50°C hotter than the outside air. A clean white roof, by comparison, runs only 5°C to 10°C warmer than the ambient air,” writes Rosenfeld in the Journal of International energy Agency (IEA).
“With roofs accounting for roughly 25% of urban surface area and with cities occupying 1% to 2% of global land area, converting most flat roofs in warm cities to white would cancel warming from more than one gigatonne of CO2 per year for the average lifetime of the roofs,” claims Rosenfeld, a nuclear physicist who turned his focus to energy efficiency more than 30 years ago.
“In terms of emissions, it’s equivalent to taking half the world’s cars off the road for 20 years,” said Rosenfeld.
New York Mayor Michael Bloomberg set up a scheme to hire young people to paint the city’s roofs white with more than 330,000 square metres already covered.
The Lawrence Berkeley National Laboratory has been responsible for a number of energy efficiency breakthroughs and has also shared much of its work with China.
The Lab’s Mark Levine worked in energy efficiency projects in China since the 1980s.
“I went to China to advise them on the establishment of their first energy efficiency ratings for appliances,” says Levine. “Once standards were in place for fridges and air conditioners they were able to make annual energy savings equivalent to twice the annual output of the Three Gorges Dam.”
The IEA has identified energy efficiency has a vital tool to reduce dependence on fossil fuels calling it “the hidden fuel”.