Polar Climate Trends Review: The Arctic
March 03, 2012; 3:53 PM
Earth's two polar regions feature markedly different geographies and not surprisingly, respond differently to global change. While the ice around the South Pole (the Antarctic) has remained relatively stable over the past 40 years, the ice around the North Pole (the Arctic) has demonstrated dramatic responses to global temperature trends.
Temperature Trends: Over the last 40 years, the Arctic has warmed at about twice the global rate. Arctic land surface temperature trends estimates run as high as 3.6 degrees Fahrenheit per decade. Similar occurrences of Arctic temperature trends moving in the same direction as global temperature trends but at more dramatic rates were experienced during the 1910-1940 warming period and during a cooling period from 1940-1970. These more dramatic rates are likely linked to the behavior of Atlantic Ocean currents, which can move greater or lesser amounts of heat to the Arctic in accordance with long-term ocean circulation cycles. The recent increase in land surface temperatures has been accompanied by some rapid changes in plant communities, with shrubs and trees now able to tolerate areas that only decades ago were too cold to support anything other than tundra sedges and grasses. Shrub and tree cover is currently expanding into the Arctic tundra at a rate of 8,600 square miles, or 0.4 percent, per year. Sea surface temperatures in the Arctic have also warmed - since 1995, they have warmed rapidly. During 2007, sea surface temperature departures from normal of nine degrees Fahrenheit were observed.
Sea Ice Trends: Over the last 30 years, there has been a 20-day, Arctic-wide increase in the length of the sea ice melt season, with the fastest trends occurring in the Hudson Bay area. Extension of the melt season has been accompanied by an overall reduction in the average annual (September) sea ice extent minimum from about 3.1 million square miles in 1979 to 2.1 million square miles in 2010: a one million square mile and ten percent per decade melt. For comparison, one million square miles is about the area of the United States east of the Mississippi. Multiyear ice - ice that has survived at least one melt season - has become rarer. The percentage of multiyear ice at the September minimum has declined by 50 percent since 1980. In March 2011, only about 45 percent of the ice present in the Arctic was multiyear ice, compared with 75 percent in March 1980. While about 50 percent of the ice cover was particularly old ice (older than five years) in 1980, that number had declined to 10 percent by March 2011. This decline in multiyear ice has become particularly pronounced in the last four years.
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