After making this dramatic statement - which is indeed correct, because of the two important "ifs" it contains - Gore approvingly quotes the United Kingdom's Sir David King as saying "the maps of the world will have to be redrawn," as if the occurrence of this hypothetical scenario was something we may expect to witness sometime in the very near future. And to visually make his point more poignant, Gore goes on to illustrate what would happen to Florida, San Francisco Bay, the Netherlands, Beijing, Shanghai, Calcutta, Bangladesh and Manhattan, suggesting that we should begin preparing now for what he implies is a serious threat commensurate with other major present-day concerns. The perspective provided by real-world science, however, is something far, far different.

In the 16 March 2007 issue of Science, which highlights the current status of polar-region science at the start of the International Polar Year, Shepherd and Wingham (2007) review what is known about sea-level contributions arising from wastage of the Antarctic and Greenland Ice Sheets, concentrating on the results of 14 satellite-based estimates of the imbalances of the polar ice sheets that have been derived since 1998. These studies have been of three major types - standard mass budget analyses, altimetry measurements of ice-sheet volume changes, and measurements of the ice sheets' changing gravitational attraction - and they have yielded a diversity of values, ranging from a sea-level rise equivalent of 1.0 mm/year to a sea-level fall equivalent of 0.15 mm/year.

Of these three approaches, the results of the latter technique, according to Shepherd and Wingham, "are more negative than those provided by mass budget or altimetry." Why? Because, in their words, the gravity-based technique "is new, and [1] a consensus about the measurement errors has yet to emerge, [2] the correction for postglacial rebound is uncertain, [3] contamination from ocean and atmosphere mass changes is possible, and [4] the results depend on the method used to reduce the data." In addition, they say that (5) the Gravity Recovery and Climate Experiment (GRACE) record is only three years long, and that (6) it is thus particularly sensitive to short-term fluctuations in ice sheet behavior that may not be indicative of what is occurring over a much longer timeframe. Even including these likely-inflated results, however, the two researchers conclude 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 rise described by Gore - a little less than an inch and a half.

Yet even this unimpressive sea level increase may be far too large, for although two of Greenland's largest outlet glaciers doubled their rates of mass loss in less than a year back in 2004, causing many climate alarmists to claim that the Greenland Ice Sheet was responding much more rapidly to global warming than anyone had ever expected, Howat et al. (2007) report - in the very same issue of Science as Shepherd and Wingham - that the two glaciers' rates of mass loss "decreased in 2006 to near the previous rates." And these observations, in their words, "suggest that special care must be taken in how mass-balance estimates are evaluated, particularly when extrapolating into the future, because short-term spikes could yield erroneous long-term trends."

In light of these many observations, we feel it should be obvious to all reasonable people that the former U.S. Vice President has implied much more than is scientifically justified about the future behavior of the Greenland and Antarctic Ice Sheets and their impacts on global sea level. Indeed, he has implied vastly more than is justified.

Sherwood, Keith and Craig Idso

References
Gore, A. 2006. An Inconvenient Truth: The Planetary Emergency of Global Warming and What We Can Do About It. Rodale, Emmaus, PA, USA.

Howat, I.M., Joughin, I. and Scambos, T.A. 2007. Rapid changes in ice discharge from Greenland outlet glaciers. Science 315: 1559-1561.

Shepherd, A. and Wingham, D. 2007. Recent sea-level contributions of the Antarctic and Greenland Ice Sheets. Science 315: 1529-1532.