Cities are typically warmer than the surrounding countryside, a phenomenon known as the heat island effect. There are numerous causes of this phenomenon, including emissions from cars and buildings. This creates a mini greenhouse effect. In rural areas, the standing water in marshes and ponds evaporates, which cools the air slightly. This does not occur to the same extent in the city. The tall buildings in the center of most cities block winds that would provide some relief from the excessive heat. Finally, the color and material of most roads and buildings absorbs rather than reflects heat. Although planting trees and using building materials that reflect heat may alleviate the problem somewhat, it will by no means eliminate it.The main purpose of the passage is to

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