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White Roofs, Re paved Roads Help Stem Global Warming


By Adam Satariano, Bloomberg

(Corrects emission-offset figure in seventh paragraph)

Sept. 12 (Bloomberg) -- To curb global warming, scientists have proposed steps as drastic as releasing reflective chemicals into the skies to bounce sun rays back into space. California researchers have a simpler idea: replace roofs and repave roads.

Using white materials on highways and on top of buildings in the world's 100 largest cities would do more to counter planet- warming greenhouse-gas emissions, scientists at the Lawrence Berkeley National Laboratory and University of California, Berkeley say.

White roofs, a common feature on the Greek island of Santorini, have been used for thousands of years to reflect heat. Applying the method worldwide would cool surface temperatures, helping offset warming caused by carbon-dioxide emissions from factories and vehicles, the researchers said.

``There are two ways that one can cool the globe,'' Hashem Akbari, a physicist at the Lawrence Berkeley National Laboratory, said in an interview. ``One is to remove a certain amount of CO2 from the atmosphere, the other is to reflect some of the incoming radiation.''

The measures would directly cut CO2 released by electricity plants because less power would be needed for air conditioners. Lighter surfaces absorb less solar radiation, helping undercut the greenhouse effect, in which gases in the atmosphere trap solar energy and heat the planet.

``A lot of scientists are constantly debating what to do, and here we have several things we can do right now,'' Akbari said.

$2 Billion Savings
In the U.S. alone the measures would produce $2 billion of savings a year in reduced energy use and improved air quality, according to data from the study made public Sept. 10. An average house with a 1,000-square-foot roof would offset the equivalent of 10 metric tons of CO2, the output of one car for two years, the researchers said.

California has required owners of buildings with flat roofs since 2005 to color them white as an energy-efficiency measure because it reduces air conditioning use. For sloped roofs, which present more architectural challenges, the state will next year begin requiring ``cool-colored'' roofing, materials that are not as reflective as white.

The International Energy Agency, adviser to 27 oil-consuming nations, has said failure to reduce greenhouse gases blamed for climate change could cause global temperatures to climb by 6 degrees Celsius (10.8 degrees Fahrenheit) by the year 2100, citing scientific studies sponsored by the United Nations.

Urban Focus
Akbari said efforts should focus on urban centers. More than half the world's population lives in urban areas, a figure that's expected to reach 70 percent by 2040, the researchers said. Meanwhile, roofs account for roughly 25 percent of the surface of most cities, while pavement accounts for about 35 percent.

The findings, scheduled to be published in the journal Climate Change, contrast with research under way to "geoengineer'' a drop in world temperatures by altering the environment. Scientists at Lawrence Livermore National Laboratory and elsewhere are examining whether the world can be cooled by injecting chemicals high into the atmosphere to help reflect the sun's rays before they can reach and warm the planet.

Akbari, along with colleague Surabi Menon and Arthur Rosenfeld, a physicist at UC Berkeley, say the best way to immediately address climate change is through simple solutions that can be quickly adopted. The team will urge the United Nations to call on major cities in tropical and temperate regions to adopt policies to ensure that more reflective materials are used when installing new roofs and roads.

``The biggest challenge is going to be implementation,'' he said.




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