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...both the extent and thickness of Arctic sea ice is certainly subject to variation. But it would be a mistake to assume that a brief period during which the Arctic is in a thinning cycle is anything more than that - a cycle. We know from past history that it has been subject to earlier retreats....Part of the problem lay in the fact that useful data on ice extent and thickness only dates from the 1950s, yet our temperature record from Jan Mayen Island at the edge of the Arctic shows that the Arctic was warmer during the 1930s than it was during the 1990s. Unfortunately there is no comprehensive ice data from the 1930s. Instead such data begins in the late 1950s, at a time when the Arctic was entering into the grip of a known cold spell. As that cold period ended, it is hardly surprising to find thinner ice during the latter warmer period. [....]The limits on the thickness of Arctic ice are determined by how low the air temperature can get, and on how warm and fast-moving the subsurface water is. Air temperatures measured in the Arctic region show no recent warming, thus discounting the possibility that recent thinning of ice could be caused by atmospheric warming above the ice. Rather, the thinning of ice in the 1990s is clearly associated with a warming of the sub-surface ocean, as shown by the SCICEX data, caused in whole or in part by the strong NAO [North Atlantic Oscillation -- ocean current change] increasing the flow rate of Atlantic water into the Arctic Ocean.
There is nothing in the data to suggest anything but natural cycles at work.