A forthcoming study in Geophysical Research Letters reinforces the idea that painting urban rooftops white — a tactic that would reflect sunlight — could have a cooling effect on the planet.
White roofs have been thought to be particularly effective in cities, which tend to be warmer than rural areas because of the presence of asphalt roads, tar roofs and other surfaces that absorb heat.
Although earlier studies have also pointed this out, in this case, the team used a computer model to simulate the amount of solar radiation absorbed and reflected by urban surfaces. The models indicated that if every roof in every city were painted white, it would reduce demand for air conditioning and ultimately cool every city by an average of about 0.7 degrees Fahrenheit.
“We think it’s really important to model the temperatures within the cities, because that’s where most of world’s population lives,” said Gordon Bonan , an author of the study and a senior scientist at the National Center for Atmospheric Research.
“This will be a very important tool to model cities and form a strategy to mitigate warm temperatures,” he said.
Other studies have found that while roofs do reduce air-conditioning costs by 20 percent in hot, sunny weather, this may be countered by the additional energy required to heat buildings during the winter months in cold climates.
Mr. Bonan said that while the study’s main findings supported the idea that painting roofs would effectively reduce global temperatures, “we also need to consider the costs of heating of buildings because of that.”
White roofs may be best suited for cities with a year-round warm climate, he said.
Last year, The Times reported on a burgeoning white-rooftop movement — which has gained the support of Energy Secretary Steven Chu, who told a “Daily Show” audience last year to, “Make it white.”
White roofs have been thought to be particularly effective in cities, which tend to be warmer than rural areas because of the presence of asphalt roads, tar roofs and other surfaces that absorb heat.
Although earlier studies have also pointed this out, in this case, the team used a computer model to simulate the amount of solar radiation absorbed and reflected by urban surfaces. The models indicated that if every roof in every city were painted white, it would reduce demand for air conditioning and ultimately cool every city by an average of about 0.7 degrees Fahrenheit.
“We think it’s really important to model the temperatures within the cities, because that’s where most of world’s population lives,” said Gordon Bonan , an author of the study and a senior scientist at the National Center for Atmospheric Research.
“This will be a very important tool to model cities and form a strategy to mitigate warm temperatures,” he said.
Other studies have found that while roofs do reduce air-conditioning costs by 20 percent in hot, sunny weather, this may be countered by the additional energy required to heat buildings during the winter months in cold climates.
Mr. Bonan said that while the study’s main findings supported the idea that painting roofs would effectively reduce global temperatures, “we also need to consider the costs of heating of buildings because of that.”
White roofs may be best suited for cities with a year-round warm climate, he said.
Last year, The Times reported on a burgeoning white-rooftop movement — which has gained the support of Energy Secretary Steven Chu, who told a “Daily Show” audience last year to, “Make it white.”
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