The Earth has warmed about 1° F over the last century.

Some of the change may be natural, but most climatologists think the greenhouse gases people produce are a big part of it. Climate models suggest that the Earth's temperature will continue to rise as long as we keep adding to the greenhouse gases in the atmosphere.

Don't think that 1° F is a big deal?

Think again. Over the last 100 years, melting glaciers and rising temperatures have caused sea level to rise six to eight inches worldwide. This could be catastrophic for low-lying countries such as Bangladesh and the Netherlands, and big cities on coastal plains or river deltas—Shanghai, Bangkok, Jakarta, Tokyo, New York, New Orleans—are also at risk.