Michelle Williamson

The melting of land ice is already raising sea levels. In some fairly likely scenarios, oceans would rise by meters worldwide with devastating results. A sea level rise of just one meter would displace millions of people in Bangladesh alone.

All of this melting ice could dilute the world's oceans changing the salinity enough to hurt fish stocks and disrupt ocean circulation patterns globally. As rising temperatures cause the ice sheets to break up faster, creating more icebergs, the amount of carbon dioxide removed will also rise.

The warming of the atmosphere caused by increases in greenhouse gases is melting glaciers and causing ocean water to warm and expand thermally. Both effects increase the volume of the ocean, raising its surface level. Eventually, if greenhouse warming continues, big changes could be in store for our planet. These so-called "doomsday scenarios" result from feedback effects -- networks of cause and effect that amplify the warming caused by the original increase in carbon dioxide. Here are a few possibilities.

Methane madness- The continental shelves harbor huge amounts of stored methane, a potent greenhouse gas in its own right. If coastal waters warm enough, this methane could be released, causing greatly increased warming. Similarly, warming in the Arctic tundra could release vast stores of carbon dioxide, with similar effects.

Ice-sheet insanity- Melting glaciers are but a trickle of water on the planetary scale. They're small change compared to the West Antarctic Ice Sheet, which holds 3 million cubic kilometers of fresh water. Were it to melt, sea level would rise 20 feet, and coastal cities, not to mention beaches, would be in tough shape.