Windy.

Every time you leave the lights on in your bedroom, you're using energy. But if your power comes from wind energy, or energy generated by the motion of air, you could be changing the weather too.

Wind energy accounts for roughly one half of one percent of the energy produced in the United States. But large wind farms--often with hundreds of 25-story-tall fanlike towers--are gaining in popularity. "When people think of wind farms, they think of a quaint, lone windmill. Yet in reality, they look more like a field of huge airplane propellers," says Somnath Baidya Roy, a climatologist (scientist who studies weather) at Duke University.

Unlike energy from pollution-causing fossil fuels, such as coal-burning power plants, wind energy has been hailed as an environmentally friendly source of power. But are these swarms of buzzing blades really harmless?

Baidya Roy created a computer model to find out. "Computer models are a way to predict the future," he says. And since wind energy is the most likely competitor of fossil fuels in coming years, Baidya Roy modeled a super-size wind farm. Much larger than any current farm, his model whirred with a whopping 10,000 turbines.

This virtual breeze-maker showed that wind farms spinning at night could increase both the wind speeds and temperatures in nearby areas. That's because when the sun sets, air near the ground gets cool and moist compared with the warm, dry air higher up. But the turbines created drafts that pulled down the warm air and pushed up the cool air.

What does Baidya Roy make of his blustery find? "Wind farms still alter weather much less than fossil fuels, which produce heat-trapping (greenhouse) gases," he says. "But the most important thing we can do is use less energy."

Did You Know?

* California has some of the largest wind farms (the most number of wind turbines in an area) in the U.S. In a 183-square-kilometer (70-square-mile) region of the Coachella Valley--located between the San Bernadino and San Jacinto mountains--there are more than 4,000 turbines.

* The windiest states in the U.S. lie within the Great Plains. If the wind in this area could be harvested by wind farms, it would produce enough energy for the entire country's needs.

Resources

* To learn how a wind turbine works, check out: www.eere.energy.gov/windandhydro/wind_how.html

* For a kid-friendly Web site on wind and windmills, go to: www.wind power.org/en/kids/index.htm