The Arctic And Antarctica

According to a report in National Geographic News on December 13, 2002, the six largest Eurasian rivers are currently dumping an excessive amount of freshwater into the Arctic Ocean—much more than they were even a few decades ago.

Bruce Peterson at the Marine Biological Laboratory in Woods Hole, Massachusetts, says, "The mechanism is most likely due to increased precipitation as forecast by global climate models."

This finding supports the long-held belief that freshwater runoff into the ocean would increase in the Arctic as a result of global warming. Other factors that may also be contributing to the situation include changes in ice and permafrost melt or changes in the seasonality of precipitation and runoff. The major concern with an increase of freshwater being deposited to the Arctic Ocean is that it could negatively affect ocean circulation patterns in the North Atlantic, thereby altering the heat distribution characteristics of the major currents. Potentially, the influx could slow down or shut off the North Atlantic Deep Water formation (referred to as the Ocean Conveyor Belt), an important current that supplies large amounts of warm water to the North Atlantic region.

Research of the amount of freshwater currently being discharged into the Arctic Ocean is currently about 31 cubic miles (128 km3) greater than it was in the 1930s. According to Bruce Peterson, "One thing that can slow the circulation of the Ocean Conveyor Belt is if you add freshwater to that area of the North Atlantic. According to several ocean circulation models, if enough freshwater is added to the Arctic Ocean, it will eventually shut down the Conveyor Belt. If you stop the process, you stop the conveyor that brings warm water north. The paradoxical result would be a cooling of northern Europe."

Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research in Germany says, "Most of the rest of the world gets warmer when the conveyor is shutdown. Ocean currents don't generate heat, they just move it around. A shut down would probably enhance global warming, since shutting down the conveyor would also reduce the ocean's uptake of CO2, so that more of our emissions remain in the air."

Evident impacts to Antarctica from global warming will likely occur first in the northern (warmer) sections of the continent, where the summer temperatures approach the melting point of water: 32°F (0°C). In recent years, some of the ice shelves in the northernmost portions of Antarctica, such as in the Antarctic Peninsula, have been collapsing. This has principally occurred during the gradual warming trend since 1945. One of the largest areas of concern for scientists studying Antarctica is the West Antarctic ice sheet on the main continent. If it were to melt, weaken, and collapse, it could raise sea levels by 19 feet (5.8 m).

According to a report in National Geographic News on March 6, 2003, when a huge floating shelf of ice hinged to the northern end of the Antarctic Peninsula disintegrated in January 1995, several glaciers that were backed up into it surged toward the sea. Its discovery provided the first absolute evidence that glacial surge follows an ice shelf collapse.

This is a key finding because it allows scientists to focus on the theory that ice shelves act as "dams" that prevent inland glaciers from slipping into the seas. For more than 30 years, scientists debated whether or not ice shelves acted as barriers for inland ice. Prior to this discovery, many models assumed the type of ground surface it was traveling across dictated the rate of glacial flow. The increased flow after the collapse of the shelf shed new light on understanding the mechanisms of movement and dynamics of the Antarctic glaciers. It is important because if the same disintegration scenario were to happen with major ice shelves such as the Ross Ice Shelf or the Filchner-Ronne, the entire West Antarctic Ice Sheet could collapse and cause global sea levels to rise 16 feet (5 m), assuming ice shelves were the only thing holding the glaciers back from the sea. This debate gives scientists an opportunity to study glacial surge and retreat in Antarctica and how their delicate balance affects ocean levels. It also allows them to get a better idea of the delicate interaction and stability between ice shelves and glacier retreat.

In another study conducted by Isabella Velicogna, a research scientist at Colorado University at Boulder's Cooperative Institute for Research in Environmental Sciences, based on data from two NASA satellites called the Gravity Recovery and Climate Experiment (GRACE), the amount of water pouring annually from the ice sheet into the ocean—equivalent to the amount of water the United States uses in three months—is causing global sea level to rise by 0.016 inch (0.04 cm) a year. Velicogna says, "The ice sheet is losing mass at a significant rate. It's a good indicator of how the climate is changing. It tells us we have to pay attention."

The Natural Resources Defense Council, Union of Concerned Scientists, Environmental Defense, National Environmental Trust, World Resources Institute, and World Wildlife Fund have identified the following global warming impacts in this region:

• Antarctic Peninsula: The warming rate is five times the global average. Since 1945, it has experienced a warming of about 4.5°F (2.5°C). The annual melt season has increased by two to three weeks in the past 20 years.

• Antarctica: Ice shelf disintegration has occurred on the Larsen A ice shelf, where 770 square miles (1,994 km2) disintegrated in

January 1995. The Larson B and Wilkins ice shelves collapsed during 1998-99, destroying 1,150 square miles (2,978 km2) of ice. In February 2002, the northern section of the Larsen B ice shelf, an area of 1,250 square miles (3,250 km2), disintegrated in a period of 35 days, making it the largest collapse of the past 30 years. The ice thickness has also been decreasing. Permanent ice cover of nine lakes on Signey Island has decreased by 45 percent since the 1950s.

• Southern Ocean: There is a strong warming trend in the waters around Antarctica. From the 1950s to the 1980s, the temperatures have risen 0.3°F (0.17°C).

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