New York's buildings and asphalt help capture the sun's light and results in warmer temperatures.

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If you can't take the heat, get out of the city. Turn on the local weather report and you'll probably notice an odd trend. Temperatures are often a few degrees higher in cities than they are in their surrounding rural areas. This temperature discrepancy is the result of a bizarre phenomenon known as the urban heat island effect.

As the name implies, the effect makes cities into islands of heat. According to the U.S. Environmental Protection Agency, temperatures in U.S. cities can get as much as 10 degrees Fahrenheit higher than their surrounding areas [source: EPA]. Normally the temperature disparity is not quite that large, but even a few degrees can make a huge difference. The demand for air conditioning in the summer leads to higher energy bills. And many argue that this increases greenhouse gas emissions from power plants that provide that extra energy. On the other hand, some point out that the reduced need for heat in the winter offsets the costs in the summer. In addition, warmer cities in the winter means fewer icy streets.

Perhaps the worst result of the heat island effect is the number of heat-related deaths. Although damage-inducing storms get the most media attention, the National Oceanic and Atmospheric Administration reports that heat is usually more deadly. In the U.S., heat typically kills more people each year than tornadoes, hurricanes, floods and lightning put together [source: NOAA].

So what creates the urban heat island effect? And how can city planners reduce it?