Natural

clipped from www.john-daly.com As we can see from recent history, 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 as suggested by the opening quote from 1817. 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 increasing the flow rate of Atlantic water into the Arctic Ocean.