Shrinking Ice, Rising Seas

Keeping a Level Head
Like something out of a supermarket tabloid magazine, the facts fit together like an environmental conspiracy. The world is getting warmer! Glaciers are disappearing! Huge pieces of ice are breaking off Antarctica and drifting north! And sea level is creeping higher and higher, threatening to flood low-lying areas from the Netherlands to Bangladesh! Should we be worrying?

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?

  • Batten Down the Hatches, Sea Level is Rising
  • Antarctic Ice Sheet Given 7,000 Years to Live
  • Antarctica Is Not Shrinking
  • World's Glaciers Continue to Shrink

Are scientists disagreeing or just looking at the same data in different ways?

A Rose Is a Rose Is an Ice Cap

"The polar ice caps are melting!" That may sound catchy, but the person saying it doesn't mean to say "ice cap" at all. The masses of ice covering Greenland and Antarctica are actually continental glaciers, the same sort of glaciers that covered much of North America during the Ice Age. They are more properly called ice sheets. Ice caps are smaller, non-valley glaciers. They are found in Iceland, Baffin Island, and other Arctic islands.

When scientists argue over melting ice and rising sea level, they usually mean not only the Antarctic and Greenland ice sheets, but also the ice caps and valley glaciers, which are found in such places as Alaska and Norway.

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 shrinking—or actually growing?

It's All Relative
Sometimes it is even difficult to know for sure that sea level is rising at all. Measuring changes in sea level isn't as easy as it sounds. One might think that with all of Earth's oceans being connected, changes in sea level would be the same worldwide. But this is not the case. The land is rising and falling, too.

IceTake 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 year—not 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.

Warming to the Idea
The biggest concern for scientists is that global warming will lead to a substantial and disastrous rise in sea level. Global warming is the slow, steady increase in average temperatures observed worldwide. Global warming is thought by many to be caused by the release of "greenhouse gases," such as carbon dioxide, into Earth's atmosphere. These gases trap heat near Earth's surface. Higher temperatures should mean that ice at Earth's poles melts faster than normal. This adds water to the oceans, causing rising sea levels.

AntarcticaEven 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.


What We Need Is Higher Higher Ground
It wouldn't take much of a rise in sea level to wash away island nations such as the Maldives in the Indian Ocean. Eighty percent of the Maldives are less than one meter above sea level. Several Pacific islands have already disappeared.

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.

The Big Uneasy

Rising sea level is the last thing the citizens of New Orleans, Louisiana, want to hear about. Much of that city is already 2 to 3.5 meters below sea level. The water from the Mississippi River is kept out of the city by artificial walls called levees. Every year, huge pumps are needed to drain the accumulated rainwater from the streets and yards.

But New Orleans is built on a delta—the land created when a river dumps its load of mud and sand at the river's mouth. The mud and sand beneath New Orleans is sinking at a rate of 1 meter-per century. Even without the threat of rising sea level, New Orleans may not exist in another 100 years.

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.

  • Read about the threats to small island nations from rising sea level.
  • How does the slope of the land near a shoreline affect the potential for flooding due to rising sea level? Review the concept of rise and run in the Destination MATH session: Mastering Algebra I: Course 1, Linear Functions and Equations, Defining Slope.

    Which would experience more flooding, a shoreline with a slope of 1 meter/10 meters, or one with a slope of 5 meters/10 meters? Draw two different right triangles to demonstrate the effect of slope on flooding.

Learn More
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