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.