Arctic Sea Ice II: The Meltdown

The loss of sea ice, when plotted on a graph (Figure 1), has roughly followed a straight line over time. There are a few noisy ups and downs, reflecting colder and warmer years than average. A trend that approximately follows a straight line is called a "linear" trend. A continued linear summertime 8% per decade loss of sea ice would leave the summertime Arctic Ocean ice-free by 2100. The ocean would still partially freeze in winter, with about 50% of the ocean covered with ice.



However, there is a distinct possibility that Arctic sea ice loss may show a sudden non-linear decline in coming years. The loss of sea ice with time may no longer follow a nice straight line, but instead suddenly accelerate, allowing the Arctic sea ice to suffer a sudden and complete disintegration in just a decade. The result would be an ice-free Arctic Ocean for the first time since before the last ice age. This possibility was explored in a December 2006 paper (Holland et al.), titled "Future abrupt reductions in the summer Arctic sea ice". The authors ran the Community Climate System Model, one of the top climate models used to formulate the "official word" on climate, the 2007 Intergovernmental Panel on Climate Change (IPCC) report. The model was run for the years 1979-2006, and successfully predicted the 20% loss of summer sea ice during that period. The model then assumed that levels of greenhouse gases would continue to increase, until a doubling of CO2 levels occurred in 2100. This is considered a "middle-of-the-road" scenario, and assumes a reasonable sequence of events will unfold over the coming decades: humans will make some modest efforts to control greenhouse emissions, but not enough to prevent dangerous climate change. The model found that Arctic sea ice continued to decline linearly until about 2024, resulting in about 60% sea ice coverage in September (Figure 2). During this period, the vertical thickness of the sea ice declined from about four meters to one meter. Beginning in 2025, the rate of sea ice loss suddenly tripled, resulting in the total loss of the summertime polar sea ice by 2040. The authors theorize that once the ice reaches a critical thickness--in this case, one meter--the processes that create open water suddenly become more efficient, resulting in a rapid disintegration of the remaining ice.



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