Volume 10, Number 15: 11 April 2007
In his 21 March 2007 testimony before the United States Senate's Environment & Public Works Committee, former U.S. Vice President Al Gore talked passionately about what he referred to time and again as a "climate crisis," which he characterized as "a planetary emergency - a crisis that threatens the survival of our civilization and the habitability of the Earth." One of the scare stories he frequently uses to promote this concept is that of half of Greenland and half of Antarctica breaking up, sliding into the sea, and raising sea levels worldwide by between 18 and 20 feet. And to attach an even greater sense of urgency to this scenario, he states in his book (An Inconvenient Truth, p. 186) that "many residents of low-lying Pacific Island nations have already had to evacuate their homes because of rising seas."
In our editorial of [need to add link] 4 Apr 2007, we described what the most up-to-date real-world science has to say about the subject, noting that "the current 'best estimate' of the contribution of polar ice wastage to global sea level change is a rise of 0.35 millimeters per year, which over a century amounts to only 35 millimeters or - to better compare it to the 20-foot sea-level rise described by Gore - a little less than an inch and a half." In this editorial we describe what the most up-to-date real-world science has to say about what some have claimed to be a much more rapid mode of ice sheet wastage: a rise in sea level or change in ice sheet thickness that leads to rapid grounding-line retreat and a huge increase in the overall rate of sea level rise, which is one of the infamous "tipping points" that climate alarmists use to (1) instill fear of imminent catastrophe in the public at large and (2) justify Mr. Gore's repetitive use of the word "crisis" in his sermonizing on the topic, as in his testimony to the U.S. Senate, where the scary word appears an amazing 10 times in his testimony's 14 brief paragraphs.
So what are the newest findings of pertinence to the topic? In the 30 March 2007 issue of Science, Anandakrishnan et al. (2007) relate their recent discovery of a grounding-line sedimentary wedge or "till delta" deposited by and under West Antarctica's Whillans Ice Stream, which they detected in the course of radar surveys made from the floating Ross Ice Shelf as part of a larger study of the behavior of the West Antarctic Ice Sheet. This grounding-line buildup of sedimentary material, as they describe it, "serves to thicken the ice and stabilize the position of the grounding line," so that "the ice just up-glacier of the grounding line is substantially thicker than that needed to allow floatation, owing to the restraint from friction with the wedge." Consequently, they say that "the grounding-line will tend to remain in the same location despite changes in sea level (until sea level rises enough to overcome the excess thickness that is due to the wedge)."
So how much sea-level rise would be required to float the Whillans Ice Stream off its grounding-line wedge and wrest it from the continent? In a companion paper that looks at the mechanics of the phenomenon in considerable detail, Alley et al. (2007) conclude that "sea-level changes of a few meters are unlikely to substantially affect ice-sheet behavior," and that a rise on the order of 100 meters might be needed to "overwhelm the stabilizing feedback from sedimentation." In fact, in a perspective article on the new findings, Anderson (2007) states that "at the current rate of sea-level rise, it would take several thousand years [our italics] to float the ice sheet off [its] bed." What is more, Alley et al. say that the ice sheet's extra thickness up-glacier from the grounding-line wedge will tend to stabilize it against "any other environmental perturbation."
With respect to the range of applicability of the findings of Anandakrishnan et al. and Alley et al., Anderson further notes that "grounding-zone wedges are common features on the continental shelf, including the Ross Sea Shelf," and that "all ice streams of the Siple Coast have an anomalous elevation and stop at the grounding line," leading him to conclude that "this mechanism for stabilization of the grounding-line is likely to be widespread." Consequently, Anderson concludes that "sea-level rise may not destabilize ice sheets as much as previously feared," which in turn suggests that sea level itself may not rise as fast or as high as previously feared. In addition, sea-level rise due to polar ice wastage is currently progressing at what could only be called a snail's pace, all of which facts lead us to wonder ... Just what make-believe world is Al Gore living in?
Sherwood, Keith and Craig Idso
References
Alley, R.B., Anandakrishnan, S., Dupont, T.K., Parizek, B.R. and Pollard, D. 2007. Effect of sedimentation on ice-sheet grounding-line stability. Science 315: 1838-1841.
Anandakrishnan, S., Catania, G.A., Alley, R.B. and Horgan, H.J. 2007. Discovery of till deposition at the grounding line of Whillans Ice Stream. Science 315: 1835-1838.
Anderson, J.B. 2007. Ice sheet stability and sea-level rise. Science 315: 1803-1804.