Arctic

There are numerous definitions of the Arctic region. The boundary is generally considered to be north of the Circle (66� 33�N), which is the limit of the midnight sun and the polar night. Other definitions are based on climate and ecology, such as the 10�C (50�F) July isotherm, which also roughly corresponds to the tree line in most of the region. Socially and politically, this region includes the northern territories of the eight Arctic states, including Lapland, although by natural science definitions much of this territory is considered subarctic.

The area is mostly a vast, ice-covered ocean, surrounded by treeless, frozen ground. It teems with life, including organisms living in the ice, fish and marine mammals, birds, land animals and human societies.

Arctic Circle

Twentieth century data for the Arctic show a warming trend of as much as 5 degrees C over extensive land areas and temperatures are rising twice as fast as they are elsewhere in the world. The ice is getting thinner, melting and rupturing and the extent of sea-ice according to the 4th IPCC Report is shrinking by 5.4% per decade. But new analysis from scientists at the National Center for Atmospheric Research and the National Snow and Ice Data Center (NSIDC), shows that the rate from 1953 to 2006 was more like 7.8 percent per decade.

The largest single block of ice in the North Pole, the Ward Hunt Ice Shelf, had been around for 3,000 years before it started cracking in 2000. Within two years it had split all the way through and is now breaking into pieces. Increased melt water flowing through moulins, acts as lubricant speeding up glacial flow. The Ayles Ice Shelf in the Canadian arctic, broke away in 2005, the largest break up of its kind in 25 years.

The ice sheets of Antarctica and Greenland could raise sea level by many metres. The palaeo-record of previous ice ages indicates that ice sheets shrink in response to warming and grow in response to cooling. The data also indicate that shrinkage can be far faster than growth. The total contribution of glacier, ice cap and ice sheet melt to sea level rise is estimated around 1.2 mm per year for the period 1993 to 2003.

The area underlain by permafrost has been reduced and has warmed. The layer of seasonally thawed ground above permafrost has thickened in some areas, and new areas of extensive permafrost thawing have developed.

The contracting northern ice cap can also accelerate global warming due to the albedo effect. The albedo is defined as the ratio of the intensity of the outgoing radiation to the incident radiation. Put simply it is how much sunlight is reflected by surface material. For instance, albedos of typical materials in the visible light range are from up to 90% for fresh snow, to about 4% for charcoal, one of the darkest substances.

Snow and ice usually form a protective, cooling layer over the the North Pole. When that covering melts, the earth absorbs more sunlight and gets hotter, known as 'postive feedback' . If a snow covered area warms and the snow melts, the albedo decreases, more sunlight is absorbed, and the temperature tends to increase.

Seasons of Change: Evidence of Arctic Warming! this is short (less than 2mins) but a great movie about changes taking place in the Arctic.

Since 1978 the northern sea ice area has shrunk significantly. The change will threaten species such as polar bears and some seals with extinction. There is real concern that an influx of fresh water into the North Atlantic could disrupt large-scale ocean currents worldwide, and alter weather patterns that could slow, or shutdown the great ocean conveyor system, that would ulimately lead to the 'snowball earth' effect.

A study by Canadian and US researchers recently published in the journal Geophysical Research Letters, says that by 2040 the ice could be completely gone during the summer. A Further study published in May 2007 shows the Arctic Ocean sea ice is melting faster than even the most advanced climate change models predict.

The study team found that, on average, 18 climate models used in a 2007 report by the Intergovernmental Panel on Climate Change (IPCC) underestimated the extent of sea-ice decline by a factor of three. "We're about 30 years ahead of what the models show," said Julienne Stroeve, lead author of the study and a researcher at the National Snow and Ice Data Center at the University of Colorado in Boulder.

Andrew Revkin from the New York Times uses an audio visual presentation to explain what it is like to be On Top of The World, and speaks about some of the research that is being conducted under the ice.

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