Tuesday, July 15, 2008

Tipping Ice

Ted Glick at Climate Crisis Coalition is sending around this chart created by the Climate Emergency Network in Australia. Glick says, "It's very striking to see what has happened with Arctic sea ice over the last 30 years--going down at a fairly consistent rate, overall--and then the precipitous drop from 2006 to 2007."

It is interesting to contrast that to the hypothetical graph that was used to illustrate the principle of tipping elements put forward by a National Academy of Sciences panel convened by William Clark of Harvard and published in the Proceedings of the National Academy of Sciences on February 12, 2008 (PNAS 105:6;1786-1793).

The panel employed ''degenerate fingerprinting'' to extract from the system's noisy, multivariate time series and forecast the vanishing of local curvature, the best example being the Atlantic meridional overturning circulation under a 4-fold linear increase of atmospheric CO2 over 50,000 years. Eventually, the circulation collapses without early warning, as I presented in greater detail in my February 13 post.

It is too soon to say that the Arctic ice cover will follow the same pattern, but the Australian graph is evocative.

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