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The strong decline of the Arctic winter sea-ice extent, as touted by the NSIDC, is largely a consequence of their unrealistic definition of the Arctic

Sea-Ice in the Arctic



There are two major organizations measuring, via satellite reconnaissance, the extent of the sea-ice in the Arctic, namely the National Snow and Ice Data Center (NSIDC) (1) and the International Arctic Research Center (IARC) (2). Their measurements differ routinely by nearly 1,000,000 km^2 ( or about 10%). Why are they so different?

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Raison d’être

Some allege that the earth’s atmosphere is heating up (3). To verify this theory of global warming, the extent of the Arctic sea-ice has been measured for a decade or longer, on a daily basis. Of course, one would think, using similar technologies and identical definitions of sea-ice coverage (a minimum of 15% coverage) by the two agencies, their measurements should be about the same, but they are not. So, why are they so different?

It’s in the Definition

It’s all in the definition of "Arctic." The NSIDC definition is essentially "the northern hemisphere," while the IARC definition is much more restrictive. Therefore, for example, the NSIDC includes in its definition of the Arctic such areas as the Bay of Fundy and the St. Lawrence River estuary, areas that are as far south as latitude 43 N, and other areas well south of the Polar Circle along the North American and Asian continents. Some former colleagues from the province of New Brunswick, Canada were highly amused by that definition. They did not think that they were from the Arctic. Nor, I am sure, do the citizens of Ottawa, Ontario, or Quebec City, Quebec, consider themselves as living in the Arctic. It may be quite cold there in winter, just like in areas of the southern plains, but that does not mean that they are part of the Arctic. The occasional frost in Florida’s citrus groves does not make them part of the Arctic either.

Trends in ice extent

The NSIDC also produces graphs showing the Average Monthly Arctic Sea-Ice Extent. For the month of December, from 1978 to 2010, this graph shows an average decline of 3.5% per decade over that time. The relatively low sea-ice extent for December 2009 and 2010 is ascribed to a strong negative phase of the Arctic Oscillation. A more practical explanation, however, is the La Nina effect. It generally produces very cold areas over the western Arctic and warmer areas over the eastern Arctic. In fact, some of the eastern parts, including James Bay and the eastern part of Hudson Bay, as well as the areas along the shores of Labrador have become frozen over only quite recently this winter. In contrast, the western part around Alaska has been in a deep freeze for most of the season now. But that still does not explain the apparent decline of the sea-ice, or does it? The Arctic Ocean does not extend evenly around the North Pole. In the west, it has only a relatively small outlet across the Bering Strait while in the east it is wide open to the Atlantic. That means that within the Arctic Circle region, the eastern boundary of the Arctic sea-ice is much more subject to annual variations resulting from wind and currents than the western one. This is also evident from the sea-ice extent for the summer months, then entirely within the Arctic circle area, where the NSIDC-observed decline over the same period is approximately one half of that found in winter. Moreover, shipping and icebreaking activities are external influences which are more prevalent in the eastern Arctic as well.

Effect of Definition

Commonly, the Arctic is defined as the area north of the northern Polar Circle, that is latitude 66.6 N [4]. When defining the Arctic in that way, the sea-ice extent varies much less from year to year for the NSIDC data, or between the two agencies’ measurements. Therefore, the strong decline of the Arctic winter sea-ice extent, as touted by the NSIDC [5], is largely a consequence of their unrealistic definition of the Arctic. [1] NSIDC; [2] IARC-JAXA Information System; [3] National Geographic; [4] Free Online Dictionary; [5] NSIDC; accessed Jan. 26, 2011.


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Dr. Klaus L.E. Kaiser -- Bio and Archives

Dr. Klaus L.E. Kaiser is author of CONVENIENT MYTHS, the green revolution – perceptions, politics, and facts Convenient Myths


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