Spill Greenland
Listen in RealAudio
Email your weather question

We've heard the horror stories. Sea level is rising. Global warming might cause the sea to rise another foot or two this century. That would be enough to wipe out island nations and threaten much of the the U.S. coast. So what's making the sea level go up?

Part of the rise is simply because the water's warmer, so it expands. Of course, there's also melting. A number of glaciers around the world have shrunk in the past few decades. The sea ice in the Arctic Ocean is only about half as thick now as it was fifty years ago. But melting ice doesn't always translate into a higher ocean. Think about a glass of soda. When the ice cubes melt in the soda, your drink doesn't spill onto the table. That's because ice takes up a bit more volume than water. Same with icebergs. If ice is already underwater, it can't spill into the oceans.

But, it's the melting ice above sea level that can in effect spill and cause sea level rise. That's why a new study of Greenland is so important. During the last warm spell between ice ages, about 150,000 years ago the world's sea level was 10 to 20 feet higher than it is now. The study shows that Greenland's ice sheet may have played a bigger role than anybody thought. The Greenland ice sits entirely on dry land. Back then the climate warmed up an incredible 40 degrees around Greenland, which undoubtedly raised the sea around the world. Even so, it apparently took a few thousand years to melt this gigantic ice cube. Hopefully it'll take just as long this time around.

The Weather Notebook's chief writer is Bob Henson. Sean Doucette is our engineer and Jay Allison is our Senior Consulting Editor. I'm Dave Thurlow.