LOS ANGELES: By planting 10 million trees and fabricating lighter-colored roofs and pavement, Los Angeles could reverse an urban “heat island” effect – caused by concrete, asphalt and heat-retaining buildings – hat has been increasing for a 100 years, according to a study by the Dept. of Energy’s Lawrence Berkeley National Laboratory. It found that Los Angeles could lower its peak summertime temperature by 5 degrees, cut air-conditioning costs by 18 percent and reduce smog by 12 percent.
By absorbing greenhouse gases, lowering urban temperatures and reducing demand for air conditioning, trees planted in cities are far more valuable in combating global warming than trees in rural areas. A well-placed shade tree in Los Angeles is worth 3 to 5 trees planted in a distant forest.
The current campaign to plant a million trees in Los Angeles is part of a free-tree program. For every dollar it spends on trees, the city expects to realize a $2.80 return from energy savings, pollution reduction, storm-water management and increased property values.
A number of major US cities have launched sizable tree-planting programs — including Washington, Baltimore, Minneapolis, Chicago, Denver and Los Angeles. Still, the decline in tree cover has accelerated since the 1970s, especially on private property and new development, according to American Forests, an environmental group in Washington that uses satellite imagery to document tree cover across the country.
Three shade trees strategically planted around a house can reduce home air-conditioning bills by about 30 percent, particularly in hot, dry cities, and a nationwide shade program could reduce air-conditioning use by at least 10 percent, according to Energy Department research.