This is an excerpt from EERE Network News, a weekly electronic newsletter.

May 07, 2003

Trees and Green Roofs Hold Promise for Urban Energy Savings

Arbor Day was April 25th, and although you might think trees have little to do with energy use, you'd be wrong. In urban areas, the great mass of concrete, steel, asphalt, and other heat-absorbing materials acts as a giant solar collector, typically raising urban temperatures 6 to 8 degrees Fahrenheit above than surrounding areas. This increases the energy used for cooling homes and businesses in urban areas. Trees can save energy by helping to shade and cool cities, reducing this "urban heat island" effect.

Two new studies on urban heat islands in New Jersey show the situation in Newark to be even worse than usual, achieving temperatures as much as 11 degrees Fahrenheit warmer than its suburbs, while Camden yielded a more normal effect of about 6 degrees Fahrenheit. New Jersey aims to start correcting that problem by planting 100,000 new trees in urban and suburban communities. See the press release from the New Jersey Department of Environmental Protection.

Another approach to cooler cities is the use of so-called "green roofs," which involve planting gardens on the flat rooftops of buildings. Green roofs can help keep the building underneath cool while also helping to reduce urban heat islands. Although more popular in Europe than in the United States, green roofs have sprouted in recent years on Chicago City Hall and a Ford Motor Company assembly plant in Dearborn, Michigan. See the City of Chicago and Ford Motor Company Web sites.

This growing interest in green roofs has led to "Greening Rooftops for Sustainable Communities," the first North American green roofs infrastructure conference, awards, and trade show, to be held in Chicago on May 29th and 30th. See the conference Web site.

For more information about urban heat islands, see the Heat Island Group on DOE's Lawrence Berkeley National Laboratory Web site.