Cities change the climate around you. In the country, there are trees, grass, lakes, and streams. In hot weather, the trees and grass cool the area around them. Lakes and rivers also cool the area around them.
But cities are not cooled in these natural ways. Cities are built of asphalt, concrete, iron, and steel. There are few trees and usually not much grass. Rain falls onto the streets and into the sewers.
When the summer sun shines, streets and buildings take in the heat; after the sun sets, the streets and buildings throw off heat into the street. Once the sun sets, the countryside cools off, but a city may stay hot all night.
Cities are hotter than the countryside in winter, too. Standing near a car with its motor running, winter or summer, you will feel the heat thrown off by the engine. The heat comes from the gasoline burned by the engine. This heat warms the air and the ground around the car. Thousands of running cars are almost like thousands of small fires burning.
Carefully put your hand near a light bulb or television set. As you can see, electricity creates a lot of heat. This heat from electricity warms the house and the outside air.
The heat given off by cities can affect the climate. Some experts even believe that cities can change the climate of the whole world. They think that air pollution may stop sunlight from reaching the earth. If less sunshine reaches the earth, the earth may become cooler.
Still other experts think the world will get warmer. If the world did get warmer, great changes would occur. Ice near the North and South poles would melt. This would make the oceans rise. Cities near oceans — like Los Angeles, Boston, and Miami — would slowly be flooded. People living in these cities would have to move to higher land.
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