Painting roofs white has been—like changing lightbulbs—one of the well-cited easy ways out of climate change. By reflecting more light and heat back to the atmosphere, a white roof should act like a natural anti-warming device, while also reducing your energy costs by keeping your house cool in the summer. Turns out, painting your roof white would be simply a massive waste of white paint.
As it is, Mark Jacobson, a professor of civil and environmental engineering at Stanford and his colleague, research student John Ten Hoeve, found in a new paper in the Journal of Climate that while white surfaces cooled houses, they also reduced cloudiness, allowing more sunlight to reach the ground. That conclusion complements a recent study by the National Center for Atmospheric Research that found that the positive effect of white roofs in the summer would be offset by a negative effect in the winter.
"There does not seem to be a benefit from investing in white roofs," says Jacobson. "The most important thing is to reduce emissions of the pollutants that contribute to global warming."
Solar panels are a better idea than white paint, he says. "The better thing to do is to put a solar panel on the roof because that not only cools the house by absorbing the sunlight to make electricity. It also offsets fossil fuel generation at power plants."
Jacobson is similarly against other geo-engineering approaches, such as the idea of pumping tons of sulphur particles into the atmosphere to reflect light back into space.
"With all geo-engineering approaches, you are not solving the problem but masking it. There are all kinds of consequences people are not aware of, and it doesn't solve the problem. You are still going to have all these greenhouse gases going into the air."
Among other debunkings in the report: the finding that "urban heat islands"—the heating effect of covering vegetation with buildings and roads—may have as much impact on the climate as greenhouse gasses.
Heat islands are an attractive explanation for two reasons. One, nobody disputes that cities produce more heat than rural areas. Roofs and sidewalks absorb more sunlight than greenery, and reduce evaporation, lessening the natural cooling effect. Cities also see more human activity, producing heat from transport, air conditioning, and the like.
Moreover, the effect of heat islands on climate change has been under-studied. Jacobson says until recently nobody had ever done research covering the global impact, including the impact of "feedbacks" between urban surfaces and the atmosphere.
But it turns out that since the Industrial Revolution only 2 to 4 percent of "gross" global warming has been caused by heat islands, while 79 percent can put down to greenhouse gasses, and 18 percent is due to "black carbon" (soot in the air that absorbs sunlight).
"Two to 4 percent is small relative to other contributors. But people who are contrarian to global warming suggest that heat islands are responsible for a large part of global warming. This and sunspots are the main arguments of climate skeptics," says Jacobson.
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