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There is no evidence that the summer ice is in imminent danger of collapse. Feedbacks in the climate system are only marginally positive. Negative feedbacks are 1. A reduction of sea ice results in increased atmospheric water vapour and hence more clouds. Cloud albedo is greater than sea ice albedo and so net short wave forcing is reduced. 2. A reduction of sea ice results in increased evaporation. Evaporation cools the surface but warms the atmosphere when it condenses. Increased surface heating will increase the condensation height resulting in more heat lost from the atmosphere to space. This is called the 'lapse-rate feedback' 3. A reduction in sea ice results in more short wave absorbed by the open ocean. Increased short wave radiation and increased melt water reduces the ocean mixed layer depth. A shallow mixed layer stratifies the ocean such that the heating is not mixed to the deeper ocean. With the heat confined in the surface layer it is lost to the atmosphere more readily and very rapidly once autumn starts. 4. Thinner ice in summer means more heat loss from the ocean in winter, resulting in stronger ice growth. Positive feedbacks are the obvious 1. Reduced sea ice means more open water and lower albedo so more heat up take and more ice melt. Thus, a simple calculation including only the positive feedback will produce an incorrect early loss of the summer ice. All GCMs show that the inevitable loss of summer Arctic ice does not influence the global climate system. Warming does not increase significantly just because the cloud which replaces much of (but not all) the ice is more reflective. The impact on the North Greenland ice sheet will hasten the regional melt rate. However, it is evident that the decline of the Greenland ice cap will take more than 1000 years. The so called 'speedup' of draining glaciers has been shown to be a transient feature as most of those 'fast' glaciers, diagnosed in 2003, have now slowed to their original speeds. Even if tide-water glaciers were all to speed up, they can only drain 10% of the ice sheet before they become grounded above sea-level. There is ample evidence that non- tidewater glaciers have not increased in speed.
Toggle Commented Jun 12, 2014 on The day the ice cap died at Arctic Sea Ice
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Jun 12, 2014