In an earlier post I proposed an asymmetrical S-shape called the Gompertz curve as a simplified, nonphysical model describing satellite-era trends in minimum sea ice extent (Figure 4). If future ice extent follows the same trend, this model predicts a September 2011 mean extent of 4.4 million km2 (confidence interval 3.5–5.3), and extent falling below 1 million km2, “virtually ice-free,” by 2024. I emphasize that extrapolating curves is a what-if exercise, not based upon physical understanding. Sometimes a statistical approach yields predictions fairly close to those obtained from more sophisticated physical models, but how well any prediction anticipates the real Arctic will be tested in the months and years ahead.
(snip)
Both area and extent are two-dimensional indexes. We have many indications that sea ice thickness, age and volume are decreasing as well, perhaps faster than area or extent. Ice volume should be a key index, but we lack time series of direct observations. The best available time series, based on modeling constrained by observations, reflects the efforts of an ice volume team (Schweiger, Zhang, Lindsay, Steele) at the Polar Science Center of the University of Washington. This group publishes a graph tracking sea ice volume anomalies estimated from their PIOMAS model (reference Zhang & Rothrock 2003).
Figure 6 applies a Gompertz model to PIOMAS mean September ice volume estimates for 1978–2010 (data courtesy of Jinlun Zhang). The Gompertz provides a good fit to volume estimates so far, which have indeed declined faster than area or extent. According to this model the year of steepest descent (2010) just passed. We cannot yet see whether deceleration has really started to occur. Figure 6 suggests that volume could drop below 2,000 km3, just over 10% of its 1978 value, by 2017 — or given the error bands, as early as 2013.
Figure (which I, XemaSab, was SHOCKED by):
http://neven1.typepad.com/.a/6a0133f03a1e37970b014e87616da4970d-piRest of the blog post:
http://neven1.typepad.com/blog/2011/04/trends-in-arctic-sea-ice-volume.html
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