a Level Head
From all of the stories in the news, month after month, it's clear that melting polar ice and rising sea level are important subjects. But what do you make of the headlines you've read or heard lately?
Are scientists disagreeing or just looking at the same data in different ways?
Researchers do agree on some predictions. A report released in March estimates that sea level will rise half a meter around the world in the next 100 years, covering tens of thousands of square kilometers of land with water. This rise in sea level will be due, in some part, to global warming and the melting of some of Earth's glaciers.
What researchers cannot agree on is whether or not the rate of sea level increase is accelerating. Sea level is definitely rising, but by how much? Is the Antarctic ice sheet shrinkingor actually growing?
Take Scandinavia for example. During the last Ice Age, Scandinavia was covered by a thick, heavy continental glacier that pushed the land down and kept it down for thousands of years. As the Ice Age ended and the ice retreated, the land started to spring back up. Today, measured sea levels in Stockholm, Sweden, appear to be falling at a rate of about 4 millimeters per yearnot because sea level is falling, but because the land is rising.
In Thailand, overuse of ground water has caused the land to sink, making it appear as though sea level has risen almost a full meter in the last 30 years.
Scientists have tried to factor out local land movements with some success. Current adjusted estimates show world sea level rising an average of 2 millimeters per year. This number has been confirmed by measurements from the TOPEX/Poseidon satellite.
to the Idea
Even this process isn't as simple as it seems. In the case of Antarctica, it is possible for global warming to actually lead to an increase in ice thickness and cause sea level to fall. The warmer the air gets, the more water vapor it can hold. Because of its location, Antarctica will stay below freezing, even if average temperatures increase worldwide. Increased water vapor over Antarctica will lead to increased snowfall, which will add more ice to the ice sheet than is lost by melting or breaking off along the edges.
However, Greenland's ice sheet would not behave the same way. This smaller continental glacier would not be able to keep up with the melting from global warming. The potential rise in sea level worldwide from the melting of the Greenland ice sheet and the world's valley glaciers is 7 meters, more than enough to spell disaster for low-lying areas.
We Need Is Higher Higher Ground
But a more devastating impact might be felt in a country like Bangladesh, where 17 million people are living on land less than one meter above sea level. Rising sea levels could only worsen flooding, which left 20 million people homeless in 1971. It would also worsen flooding from cyclone-related storm surges, such as the one in 1972 that killed 125,000 people.
In the United States, less than half a meter of sea level increase would submerge 10,000 acres of land on Massachusetts' Cape Cod. Much of Florida would be under water with an increase of less than five meters. Coastal wetlands would disappear along the Atlantic and Gulf coasts. There would be massive beach erosion, increased flooding, and saltwater intrusion into estuaries.
Is all of this going to happen? No one can say. But with the possibility of sea levels rising a minimum of half a meter in the next 100 years, it's clear that this will continue to be something to watch, to study, and to discuss.