Urban heat islands barely contribute to global warming

While cities radiate with higher temperature than the rural world, the urban heat island effect might play less of a role in global warming than you might imagine.

While cities radiate with higher temperature than the rural world, the urban heat island effect plays less of a role in global warming than you might imagine.

Researchers from Stanford University have found that the urban heat island effect plays only a small part in global warming.

"Between 2 and 4 percent of the gross global warming since the Industrial Revolution may be due to urban heat islands," said Mark Jacobson, a professor of civil and environmental engineering from Stanford University who led the study. That's compared with greenhouse gases which have lead to a gross warming of about 79 percent and black carbon which has contributed about 18 percent.

But while urban heat islands might not have a large impact globally, they still contribute to local problems of air pollutions and poor health. And one cheap proposed solution, painting roofs white, does cool urban surfaces, but has a negative impact globally. Computer models show that if cities painted all their rooftops white it would results in an increase in global warming because it would reduce cloudiness.

"Cooling your house with white roofs at the expense of warming the planet is not a very desirable trade-off," Jacobson said. "A warmer planet will melt the sea ice and glaciers faster, triggering feedbacks that will lead to even greater overall warming. There are more effective methods of reducing global warming."

So what can cities do to reduce heat islands and global warming. The study says the answer might lie with rooftop solar panels. Not only do they produce electricity but they also absorb sunlight so that building materials don't.

"Photovoltaic panels do not reflect the sunlight back to the air, unlike white roofs, reflected light is not available to be absorbed again by pollutants in the air, creating heat," according to the study.

Sorry New York City, you might want to return all that white paint and make the investment in solar panels.

Photo: bobtravis/Flickr

This post was originally published on Smartplanet.com

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