The rest of the media is finally catching up to my post from last month (see “Another AGU stunner: Evidence that Antarctica has warmed significantly over past 50 years“).
That’s because Nature published the peer-reviewed paper that was first reported at the American Geophysical Union meeting and Nature‘s own blog (!), “Warming of the Antarctic ice-sheet surface since the 1957 International Geophysical Year” (subs req’d, abstract below).
Scientists know the Antarctic ice sheet is losing mass “100 years ahead of schedule” (see “AGU 2008: Two trillion tons of land ice lost since 2003” and “Antarctic ice sheet hits the fan“).
It is really only the warming of the West Antarctic Ice Sheet (WAIS) that you should worry about (at least for this century) because it’s going to disintegrate long before the East Antarctic Ice Sheet does — since WAIS appears to be melting from underneath (i.e. the water is warming, too), and since, as I wrote in the “high water” part of my book, the WAIS is inherently less stable:
Perhaps the most important, and worrisome, fact about the WAIS is that it is fundamentally far less stable than the Greenland ice sheet because most of it is grounded far below sea level. The WAIS rests on bedrock as deep as two kilometers underwater. One 2004 NASA-led study found that most of the glaciers they were studying “flow into floating ice shelves over bedrock up to hundreds of meters deeper than previous estimates, providing exit routes for ice from further inland if ice-sheet collapse is under way.” A 2002 study in Science examined the underwater grounding lines–the points where the ice starts floating. Using satellites, the researchers determined that “bottom melt rates experienced by large outlet glaciers near their grounding lines are far higher than generally assumed.” And that melt rate is positively correlated with ocean temperature.
The warmer it gets, the more unstable WAIS outlet glaciers will become. Since so much of the ice sheet is grounded underwater, rising sea levels may have the effect of lifting the sheets, allowing more-and increasingly warmer-water underneath it, leading to further bottom melting, more ice shelf disintegration, accelerated glacial flow, and further sea level rise, and so on and on, another vicious cycle. The combination of global warming and accelerating sea level rise from Greenland could be the trigger for catastrophic collapse in the WAIS (see, for instance, here).