For at least tens of thousands of years, changes in sea level seem to be a natural part of the earth's environment. Up until a few hundred years ago, these changes, both up and down, occurred due to land movement, ice melting from glaciers, and an increase or decrease in the amount of water trapped in the polar ice caps. In most cases, the changes were very gradual in human terms. But in the past several decades, many scientists have become alarmed at the rapid increase in ocean levels.

The reason is because the earth is heating up, which causes sea water to expand in volume and ice caps to melt. Over the past 100 years, scientists have measured a mean sea level rise of about 4 in (10 cm). They blame it on an average increase of 1.8°F (1°C) in world-wide surface temperatures of the planet...