This column is provided as a public service by the Geophysical Institute, University of Alaska Fairbanks, in cooperation with the UAF research community. Ned Rozell is a science writer at the institute.

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The polar ice cap is melting, and the fresh water released into the ocean could cause another ice age, according to several scientists who authored recent studies.

In the December issue of Geophysical Research Letters, researchers using sonar aboard nuclear submarines reported the floating ice covering the Arctic Ocean has become about 40 percent thinner than it was 20 to 40 years ago. In another study, Ola Johannessen of the Nansen Environmental and Remote Sensing Center in Norway used satellite data to determine the perennial ice cover of the Arctic ice sheet has shrunk by 14 percent over the last 20 years. In a third study, nine researchers used five different sources to determine that sea ice in the Northern Hemisphere has decreased by about 7 percent in the last 46 years. All numbers point to a drastic decrease in the amount of sea ice on top of the world.

Another study done with computer models suggests that the melting is too severe to be created by natural causes alone, and is probably related to human activity. Whatever the cause, incredible amounts of fresh water are being added to the salt water of the world’s oceans. Some scientists think the fresh water increase could cause another ice age.

Global warming and the melting of ice may cause the world to become colder due to fresh water’s effects on ocean circulation. In what scientists call the oceanic conveyor belt, heat from the tropics is carried northward, warming the North Atlantic Ocean and the land it touches.

Saltier, heavier water sinks to the deep ocean around southern Greenland and kicks the oceanic conveyor belt in motion. The heavier water is replaced by water from near the equator, which warms the North Atlantic. Without this warm water current, the British Isles and similar areas might be as cold as northern Canada.

Fresh water from the melting polar ice cap might slow the conveyor belt by diluting the salty waters of the north. It’s happened before. In a recent issue of Nature, Carsten Ruhlemann of the University of Bremen in Germany examined the chemistry of ocean sediments and determined that when the world came out of the last ice age, the oceanic conveyor belt slowed to a stop.

Two cold spells that might have been related to a fresh water increase in the ocean occurred around 15,000 years ago and 12,000 years ago. Fifteen-thousand years ago, the North Atlantic was choked with icebergs released from glaciers on a warming North America. As the icebergs melted, they released fresh water that may have stopped the currents driving the oceanic conveyor belt. The Younger Dryas event, the name for a global cooling that occurred 12,000 years ago, might also have been triggered by a similar release of fresh water into the oceans.

If the addition of fresh water causes the oceanic conveyor belt to break down again, the shrinking polar ice cap won’t be the only culprit. An ice sheet on Greenland is losing about two cubic miles each year to the sea. Closer to home, glaciers in Alaska are adding impressive amounts of fresh water to the world’s oceans. Geophysical Institute researchers recently found that the Harding Icefield on the Kenai Peninsula shrunk the height of a five-story building during the past 40 years, adding enough fresh water to the ocean to raise Earth’s sea level by one-tenth of a millimeter.

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