Urban heat islands not major contributor to warming, study shows

Oct. 21, 2011, 2:24 a.m.

Cities acting as “urban heat islands” do not significantly affect the overall warming of the planet, according to a study completed by environmental engineering professor Mark Z. Jacobson and graduate student John Ten Hoeve, who studies in the same department.

Cities do produce more heat than surrounding areas, however, according to the study, this only contributes two to four percent of the total warming since the Industrial Revolution, compared to 18 percent from black carbon and 79 percent from greenhouse gases.

This study directly contradicts some climate skeptics, who have argued that this urban heating effect contributes more than greenhouse gases.

“This study shows that the urban heat island effect is a relatively minor contributor to warming, contrary to what climate skeptics have claimed,” Jacobson said in an interview with the Stanford Report.

“Greenhouse gases and particulate black carbon cause far more warming,” he added.

The study was the first that directly addressed urban heat islands on a global scale, evaluating their effect on sea-surface temperatures, sea ice, atmospheric stability, aerosol concentrations and other factors.

Another interesting result the study found was the ineffectiveness of white-roofs. Though painting roofs white has been touted as a way to reduce global warming, Jacobson found that it in fact contributed to global warming by reflecting sunlight back into the atmosphere, reducing cloudiness and increasing the absorption of pollutants.

“There does not seem to be a benefit from investing in white roofs,” said Jacobson. “The most important thing is to reduce emissions of the pollutants that contribute to global warming.”

“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.”

One such method is installing photovoltaic panels on roofs, which absorb sunlight and convert it to energy rather than reflecting it.

The study was funded by NASA and the U.S. Environmental Protection Agency.


Brendan O’Byrne


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