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Friday, March 20, 2009

Consequences of Arctic amplification -- Complete loss of the Greenland ice sheet and the clathrate gun effect

Consequences of Arctic amplification -- Complete loss of the Greenland ice sheet and the clathrate gun effect

from the blog, March 19, 2009

The thawing of the Arctic might have global effects. Quantities of carbon exist in the form of methane stored in permafrost and clathrates. A loss of sea ice cover is expected to cause the increasing release of this stored methane back into the atmosphere. While the carbon locked up in this methane was absorbed from the atmosphere in the form of CO2, it will be re-released largely as gaseous methane, which is a potent greenhouse gas. However, recent atmospheric methanes levels show little increase, and current atmospheric methane concentrations are far below IPCC projections.

Sea ice

The sea ice in the Arctic region is in itself important in maintaining global climate due to its albedo (reflectivity). Melting of this sea ice will therefore exacerbate global warming due to positive feedback effects, where warming creates more warming by increased solar absorption.

Projected change in polar bear habitat from 2001–2010 to 2041–2050

April 3, 2007, the National Wildlife Federation urged the U.S. Congress to place polar bears under the Endangered Species Act. Four months later, the United States Geological Survey completed a year-long study which concluded in part that the floating Arctic sea ice will continue its rapid shrinkage over the next 50 years, consequently wiping out much of the polar bear habitat. The bears would disappear from Alaska, but would continue to exist in the Canadian Arctic Archipelago and areas off the northern Greenland coast. Secondary ecological effects are also resultant from the shrinkage of sea ice; for example, Polar Bears are denied their historic length of seal hunting season due to late formation and early thaw of pack ice.

Loss of permafrost

Main article: Arctic methane release

Sea ice loss has melting effects on permafrost, both in the sea, and on land and consequential effects on methane release, and wildlife. Some studies imply a direct link, as they predict cold air passing over ice is replaced by warm air passing over the sea. This warm air carries heat to the permafrost around the Arctic, and melts it. This thawing of the permafrost might accelerate methane release from areas like Siberia.

Clathrate gun

Main article: Clathrate gun hypothesis

Sea ice serves to stabilise methane deposits on and near the shoreline, preventing the clathrate breaking down and outgassing methane into the atmosphere. Any methane released to the atmosphere will then causing further warming. Should the gain of this feedback loop be sufficiently high, a ‘runaway’ process will occur. This is known as a clathrate gun effect.

Loss of Greenland Ice Sheet

Greenland’s ice sheet contains enough fresh water as ice to raise sea level worldwide by 7 metres (23 ft.). Models predict a sea-level contribution of about 5 centimetres (2 in.) from melting in Greenland during the 21st century. It is also predicted that Greenland will become warm enough by 2100 to begin an almost complete melt during the next 1,000 years or more. It is viewed by some scientists that wholly inadequate attention is being given to this issue.

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