Shepherd, A., Wingham, D.J., Mansley, J.A.D. and Corr, H.F.J. 2001. Inland thinning of Pine Island Glacier, West Antarctica. Science 291: 862-864.
In highlighting Shepherd et al.'s article in This Week in Science, Science magazine's Supervisory Senior Editor Phillip D. Szuromi begins his brief "Thinning Ice" summary
(p. 785) by stating that "the West Antarctic Ice Sheet contains enough water to raise sea level by 5 meters if it were to melt completely." This being the case, and in view of the fact that most Antarctic ice discharge is provided by ice streams, he says that "glaciologists (and the rest of us) would like to know sooner rather than later if ice loss by streaming is accelerating."
Sounds like a pretty serious problem, alright. Guess we better review the article and see what the answer is.
What was done
The authors used satellite altimetry and interferometry to determine the rate of change of ice thickness of the entire Pine Island Glacier drainage basin between 1992 and 1999.
What was learned
It was determined that the grounded glacier thinned by up to 1.6 meters per year between 1992 and 1999.
What it means
The authors note, first of all, that "the thinning cannot be explained by short-term variability in accumulation and must result from glacier dynamics." And since glacier dynamics typically respond to phenomena operating on time scales of hundreds to thousands of years, this observation would argue against 20th century warming being a primary cause of the thinning. Shepherd et al. additionally say they could "detect no change in the rate of ice thinning across the glacier over a 7-year period," which also suggests that a long-term phenomenon of considerable inertia must be at work in this particular situation.
But what if the rate of glacier thinning, which sounds pretty dramatic, continues unabated? The authors state that "if the trunk continues to lose mass at the present rate it will be entirely afloat within 600 years." And if that happens? They say they "estimate the net contribution to eustatic sea level to be 6 mm."
So let's see. That means that each century of the foreseeable future, we can expect global sea level to rise by approximately one millimeter - that's one one-thousandth of a meter, or about the thickness of a common paper clip. Yes, it's a catastrophe alright ... a catastrophe of ridiculous hype.