2. An urgent need for observations in the changing Arctic.(Arctic Observing Network: Toward a U.S. Contribution to Pan-Arctic Observing)

On 16 August 2007, satellite passive microwave monitoring of Arctic sea ice extent revealed that it had equaled the record minimum that had been achieved only two years earlier on 20 September 2005. Subsequently, on 16 September 2007, a new record minimum sea ice extent of 4.13 million square kilometers occurred (NSIDC, 2007; Figure 2). National Snow and Ice Data Center (NSIDC) scientists described the September 2007 ice extent as "quite astounding", and, having "completely shattered that old record", the ice is in a "strong spiral of decline".

On 2 October 2007, Polyakov et al. (2007) described a mooring-based observing system that shows the continued transition of the Arctic Ocean to a warmer state (Figure 3), and suggested that the lowest sea ice extent has yet to be seen. While it is reasonable to predict that continued warming of the Arctic Ocean will cause further loss of sea ice, the ice loss in 2007 was attributed to atmospheric influences, particularly a persistent high pressure system that promoted clear skies and warm, southerly air flow that combined to increase ice melting and movement away from the Siberian shore (NSIDC, 2007). Clearly, continued monitoring of the ocean and atmosphere are vital for determination of their relative influence on the sea ice cover.

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The 2007 sea ice extent observations mean that the annual rate of sea ice loss continues to exceed even the most aggressive model predictions from the Intergovernmental Panel on Climate Change Fourth Assessment (IPCC, 2007). The latter currently predict that the sea ice will diminish to zero during summer as early as 2050 or as late the early 22nd Century. Continued observation of sea ice extent, and improved spatial and temporal resolution in the observation of sea ice thickness and albedo will help to improve computer models and their predictions, lead to better understanding of the causes and consequences of the changing sea ice-climate system, and inform natural resource development and maritime transportation in an ice-diminished Arctic. There may be economic advantages in a much-reduced, or even zero, end-of-summer Arctic sea ice cover. For example, it is believed that it would allow increased natural resource exploitation and maritime transportation, with shorter routes between European, Asian and North American markets. In response to the potential for increased shipping in the Arctic, in 2004 the Arctic Council commissioned an Arctic Marine Shipping Assessment (AMSA). Increased access to the Arctic Ocean also raises questions about national security and sovereignty.

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Increased ship traffic, however, increases the likelihood of pollution in waters where clean-up, of an oil spill, for example, would be difficult, to say the least. Pollution would compound the stress on marine ecosystems that are under pressure as they adjust to the receding ice cover. The possible consequences of sea ice change on the marine ecosystem are exemplified by the polar bear population, which, according to a US Geological Survey report on 7 September 2007, could be reduced by 66% by the middle of this century (USGS, 2007).

The IPCC4 report (IPCC, 2007) notes that "Understanding and evaluating sea ice feedbacks is complicated by the strong coupling to polar cloud processes and ocean heat and freshwater transport. Scarcity of observations in polar regions also hampers evaluation". IPCC4 stresses the importance of improving atmospheric observation, specifically aerosol and cloud measurements, since the largest uncertainty in climate sensitivity is due to cloud feedbacks, with low clouds making the largest contribution to uncertainty.