PHOTO: Earth Pledge Green roofs, like this one on East 38th Street, can cool a roof by 100 degrees in the summer.

ith few green spots in New York City, there is little else beside concrete, brick and tar to absorb the heat of the summer sun. New Yorkers might not know urban heat island effect by name, but they know it by the steam that rises from the city's August streets long after the sun has set.

New York in the summer can be up to 5.4 degrees warmer than surrounding areas. There are few places to escape summer in New York, except perhaps the Hamptons for those who can afford it. But within the city, there are only Central Park and window-unit air conditioners.

Earth Pledge, a non-profit environmental group, is trying to change all this - one roof at a time. The group, founded in 1991, is working to create oases and cool spots in a hot city through ecologically friendly roofs, called green roofs.

On a hot day, the average New York City rooftop can get as hot as 175 degrees. Green roofs keep the temperature right at 75 degrees, said Colin Cheney, Earth Pledge Green Roof Initiative coordinator. Energy experts say greening New York roofs could save as much as $16 million a year in heat-related energy costs.

"We know how much vegetation will cool a city. That's why parks are so viable," Cheney said. "Imagine what New York would be like without Central Park. Some people call it the lung of New York."

PHOTO: Earth Pledge Tomatoes ripen in the Earth Pledge rooftop garden.

Green roofs are more like small Central Parks than the potted plants on Park Avenue rooftops, although they currently take close to a Park Avenue salary to create - something Earth Pledge is working to change.

Rooftops become their own ecosystem, using new technology to simulate a garden or meadow, without having the weight of one. They can be gardens of vegetables or flowers; meadows of small plants, even trees -- just not many of them.Green roofs are basically backyards - hundreds of feet up in the air.

The green roofs concept began in Germany during the late 1960s, and has taken over many American cities in the last decade. Portland, Ore., and Chicago have been putting in place environmentally-friendly roofs, including the roof of Chicago's city hall. Earth Pledge began their initiative in the spring of 2002 with their own green roof garden on top of their East 38th Street townhouse.

"Leslie Hoffman, our executive director, is an avid gardener. She loved the idea of having a garden in the city," Cheney said. And that love of gardening and of a city that has so little of it has caused this small band of New Yorkers to look toward researching ways to create more green space. To give New York, at least from above, the feel of the wilderness it was when the Dutch came to its shores in 1624.