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Study finds white and green roofs offset urban warming, reduce greenhouse gas

White roofs can reduce urban heating and carbon pollution.
White roofs can reduce urban heating and carbon pollution.
American Geophysical Union photo by Maria-José Viñas via USA Today

The results of a study published in the Proceedings of the National Academy of Science on February 10, showed that white roof installation can entirely offset the summer temperature increases associated with the landscape changes and increased greenhouse gas emissions caused by urban expansion.

The authors examined six major metropolitan areas in Arizona, California, Florida, Texas, the Mid-Atlantic, and the Midwest, and concluded in some areas urban expansion by itself could raise summer temperatures 3.6 degrees Fahrenheit by 2100. On top of that rising temperatures increase greenhouse gasses due to increased demand for air conditioning.

The federally funded study’s climate models found that white roofs could entirely offset this urban expansion warming, as well as some of the warming due to greenhouse gas emissions.

As more people move to urban areas, keeping cities cool in the summer is becoming increasingly important. Cities currently house over 80 percent of the country’s population. In the U.S., cities currently cover a total of 106,386 square miles. The U.S. Environmental Protection Agency predicts the urbanized area of the U.S. will double by 2100.

In urban areas there is a heat-island effect, which is caused by asphalt pavement and dark building surfaces. This effect can make temperatures as much as 10°F hotter than greener areas. Higher summer temperatures lead to increased energy costs and a greater occurrence of heat waves which harm human health.

The study found that white roofs are less beneficial in the colder climates of the northern U.S. than in warmer areas because they increase heating costs in the winter. In those climates, green roofs might work better.

“We find that geography and season matters. Adaptations that work at location A might not be feasible for location B,” said Matei Georgescu, an assistant professor at Arizona State and lead author of the new study.

The solution might be to use white roofs in warmer climates, and green roofs in colder climates to even out the benefits.

An earlier study done in 2010 by the Lawrence Berkeley National Laboratory said cool roofs and pavements can not only help cities stay cooler but also cool the world. They could offset the heating effect of up to two years of global carbon emissions. It estimated that converting all eligible urban flat roofs in the tropics and temperate regions to white (and sloped roofs to cool colors) could offset the emissions of 300 million cars for 20 years.

A more recent Berkeley Lab study found white roofs are more cost-effective than black or green ones over a 50-year period when installation, maintenance and a building's subsequent energy use are considered. It said they cost $2 less per square foot than black roofs and $9 per square foot less than even the least expensive green roofs.

That study’s author, Arthur Rosenfeld, when he released the findings said:

"White roofs win based on the purely economic factors we included, and black roofs should be phased out. White and green roofs do a good job at cooling the building and cooling the air in the city, but white roofs are three times more effective at countering climate change than green roofs."

Climate change is perhaps the most serious problem facing our nation. We are handicapped because the fossil fuel industry has purchased the services of so-called scientists who publish flawed and downright erroneous studies indicating that climate change is not real, and man has nothing to do with it. Then, the fossil fuel folks purchase the services of members of Congress, mostly Republicans, who tout these phony studies to call climate change a hoax.

A perfect example of this was Tennessee Republican Marsha Blackburn’s recent performance on NBC’s Meet the Press on Sunday where she “debated” climate change with Bill Nye. Blackburn insisted scientists did not agree that climate change is real, and if it is, we need to do a cost-benefit analysis before we do anything about it. In Blackburn’s mind apparently, there is little benefit to saving the planet for our grandchildren to offset the costs to the fossil fuel industry’s profits.

To save our planet we need to fight carbon pollution on all fronts. Perhaps changing roofs and even pavement colors could be one way.

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