Greenland Tipping Point
The Greenland Ice Sheet blankets 81 percent of Greenland Island. This monstrous ice slab stretches 2,480 km long and up to 750 km wide. It contains roughly 8 percent of all of Earth’s fresh water. Greenland’s Ice Sheet matters for four reasons: (reference)
As the Greenland Ice Sheet melts, sea level rises. It is a direct, proven effect. This is the biggest reason for concern over Greenland. Scientists estimate that if the entire ice sheet melted, sea level would rise 7 m. Depending on how rapidly such a change occurred, it could be a global-scale catastrophe because nearly one-third of the world’s population lives in or near a coastal zone. The global impact of several billion refugees and the negative impacts on coastal economic activity would be staggering.
A sea level rise of only 0.6 to 0.9 m would create serious global problems: increased coastal erosion, salt water encroachment, loss of barrier formations (islands, sand bars, and reefs), and increased storm surge damage. Through the 1990s, sea level rose at a rate of about 3 mm per year. The rate crept up to almost 4 mm per year by the end of last decade. For historical perspective, sea level has risen more than 380 feet since the last ice age 18,000 years ago. That’s an average rate of 10 cm per decade, or 10 mm per year. However, most of that rise occurred as the ice age ended. Sea level has been relatively stable for the past several millennia.
Sea level rise is not the only effect of a melting Greenland Ice Sheet. If the Greenland Ice Sheet melts at a faster rate, it will spread a slick of fresh water on top of the heavier salt water of the North Atlantic. This change in salinity could depress the Gulf Stream and alter North Atlantic circulation patterns that control weather in Europe. Combined with a loss of Arctic sea ice, this effect could radically change global ocean circulation patterns.
The loss of Greenland ice mass would affect global atmospheric heat movement. Any heat transfer is driven by a temperature difference. The greater that difference, the faster heat flows. As the polar regions warm, the temperature difference between the equator and the poles is reduced, altering global atmospheric circulation patterns by reducing the force that drives equatorial heat energy toward the poles. Much of the world’s current pattern of rainfall would be altered.
Regional atmospheric circulation
On average, the top 2,560 m of Greenland is ice. Like a mountain range, this physical mass affects regional atmospheric circulation patterns. If (as) Greenland’s massive range of ice melts, regional circulation patterns will also change.
Crack in the Petermann Glacier
Covering some 1,295 square km along the northwestern coast of Greenland, Petermann Glacier’s floating ice tongue is the Northern Hemisphere’s largest, and it has occasionally calved large icebergs. Between 2000 and 2001, the glacier lost nearly 87 square km. Between July 10 and July 24, 2008, the glacier lost another 29 square km. Researchers at the Byrd Polar Research Center at Ohio State University, however, expressed greater concern at the presence of a rift farther upstream. (reference)
The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite captured the following image of the rift on the Glacier on September 7, 2008. The rift, which appeared by 2001, is filled with thin ice and covered with snow in the close-up image (top). A thin fracture near the edge of the rift, however, indicates that it has continued to widen.
Image of the rift on the Petermann Glacier on September 7, 2008
After its initial formation, the rift on Petermann Glacier advanced toward the glacier front, widening as it moved. Satellite images from the 1990s show that rifts have developed in this region on the Petermann more than once, but previous rifts evolved differently than this one, which grew wider and longer. Byrd Polar Research Center scientists stated that if this rift extended completely across the glacier, the glacier could lose another 160 square km. As the glacier squeezes past the fjord walls, the interaction of the ice and rock produces backstress that keeps the ice relatively compressed. But as pieces of ice break away from the glacier, the backstress is reduced, and the glacier begins to stretch. The rift on this glacier is evidence of the glacier’s stretching and thinning over time.
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