Cooler breezes

With spring here, it won't be long before city streets are egg-frying hot and the sun's full blast is whipping tornadoes down skyscraper canyons.

Who needs the Sahara?

Just 10 miles away in the burbs, it will be pleasantly warm and breezy. The best of summer.

And this is what concerns scientists. Urban "heat islands" are not just making life a sweatshop for city dwellers, they're also tampering with local weather patterns.

The culprits are large stretches of asphalt with little vegetation.

Although heat-generating mega-cities are not new, their number is growing rapidly as the world's population moves to town. By 2025, 82 percent of inhabitants will live in urban areas, the Population Reference Bureau reports.

Perhaps the clearest example of this weather shift in America is in Atlanta, which has been uprooting 55 acres of trees a day for 20 years to accommodate its sprawl.

The result is a "dome" of hot air that hangs over the city.

Two strategies are helping offset this heat haze, says Jeffrey Luvall, a senior research scientist at Marshall Space Flight Center, in Huntsville, Ala: Planting trees and more green spaces keeps building surfaces and parking lots cooler; and using light colors on roofs and roads - concrete rather than asphalt - reflects sunlight.

The results are instant, Dr. Luvall says. In Salt Lake City, where the streets were built to turn a 20-mule team wagon, a local city engineer converted one avenue into a concrete parkway with a wide green median and trees. Remote-sensing technology used in airplanes to detect heat spots immediately picked up the cooler road.

Recently, the EPA joined the effort and offered voluntary credits to states that create "heat island" mitigation strategies.

You can still fry an egg, of course. You may just have to do it at home.

(c) Copyright 2001. The Christian Science Monitor