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Trends in Arctic Sea Ice Extent

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XemaSab Donating Member (1000+ posts) Send PM | Profile | Ignore Wed Apr-06-11 04:35 PM
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Trends in Arctic Sea Ice Extent
Proxy evidence suggests that the recent declines in Arctic sea ice extent and volume are unprecedented over at least the last few thousand years (Polyak et al. 2010). Historical records indicate that the seasonal ice zone, an area of northern seas that is ice covered in winter but not in late summer, has been expanding gradually since 1870, and more rapidly in the past three decades (Kinnard et al. 2008). Reinforcing that conclusion, combined submarine and satellite measurements show that ice has been thinning over much of the Arctic Ocean since the 1950s, so the remaining cover increasingly consists of thinner seasonal ice (Kwok & Rothrock 2009).

These longer-term studies place recent satellite-era change in perspective. Sea ice extent, in particular, has been relatively straightforward to define and measure by satellite. As a result, we have daily time series of extent and area going back into the 1970s, which confirm a recently accelerating decline. Decline has been most noticeable in late summer, but is visible across all times of the year. A cycle plot (Cox 2006) in Figure 1 illustrates changes in average extent and area (NSIDC data) broken down for each month, from November 1978 through March 2011.

Each squiggly line in Figure 1 tracks the mean sea ice extent (blue) or area (orange) for a particular month over roughly the years 1978 to 2011. The vertical axis shows the absolute ice cover in millions of km2. Extent, for example, ranges from values near 16 million km2 in winters of the earlier years, to 5 million km2 or less in summers of recent years.

The declines visible in Figure 1 all are statistically significant. Figure 2 graphs the linear trends separately for each month.


Neven's post goes on to predict what the lows should be based on linear and non-linear models. Linear = 5.2 and non-linear = 4.4

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