Bindschadler (1998) analyzed the historical retreat of the West Antarctic Ice Sheet (WAIS) in terms of both its grounding line and ice front, finding that the retreat of the former has been faster than the retreat of the latter, which has resulted in an expanding Ross Ice Shelf.  In fact, he reports, "the ice front now appears to be nearly stable."  Nevertheless, the grounding line seems to be retreating at a rate that suggests complete dissolution of the WAIS in another 4,000 to 7,000 years.

Such a retreat would likely result in a sustained sea level rise of 8 to 13 cm per century.  However, even the smallest of these rates of rise would require, in Bindschadler's words, "a large negative mass balance for all of West Antarctica," and there are as yet no broad-based data to support that scenario.  Hence, although different portions of the WAIS display different grounding line retreat rates and local mass balances, all data considered together do not suggest any imminent change of a significant nature in response to the apparent warming of the planet over the last century.

In another Antarctic study, Anderson and Andrews (1999) employed radiometric dating and conducted grain size and foraminiferal analyses on sediment cores collected from the eastern Weddell Sea continental shelf and the western Weddell Sea deep-sea floor in an attempt to better understand the dynamics of East and West Antarctic ice sheet behavior.  They report their combined data "indicate that significant deglaciation of the Weddell Sea continental shelf took place prior to the last glacial maximum" and that the ice masses that border the Weddell Sea today "are more extensive than they were during the previous glacial minimum."

These findings suggest, in Anderson and Andrews' words, "that the current interglacial setting is characterized by a more extensive ice margin and larger ice shelves than existed during the last glacial minimum, and that the modern West and East Antarctic ice sheets have not yet shrunk to their minimum."  Hence, because of the great inertial forces at work over long time scales, it is actually to be expected, independent of what global air temperature may currently be doing, that the modern East and West Antarctic ice sheets will continue to shrink and release ever more icebergs to the Southern Ocean over the coming years, decades and centuries.  Nothing man has done is responsible for these phenomena; and nothing man can do will impact them in any way.

On the other hand, Oppenheimer (1998) reviewed a number of studies that broach the question of the stability of the WAIS and its effects on global sea level, concluding that "human-induced climate change may play a significant role in controlling the long-term stability of the West Antarctic Ice Sheet and in determining its contribution to sea-level change in the near future."  Other of his statements, however, seem to challenge this conclusion.  He notes, for example, that the Intergovernmental Panel on Climate Change (IPCC) "estimated a zero Antarctic contribution to sea-level rise over the past century, and projected a small negative (about -1 cm) contribution for the twenty-first century."  Furthermore, with respect to possible anthropogenic modification of the behavior of the atmosphere and ocean above and around Antarctica, he states that "measurements are too sparse to enable the observed changes to be attributed to any such [i.e., human-induced] global warming."  With respect to sea-ice extent, for example, he states that "the IPCC assessment is that no trend has yet emerged."

Oppenheimer concludes his review with four scenarios of the future that are based upon various assumptions.  One is that the WAIS will experience a sudden collapse that causes a 4- to 6-m rise in sea-level within the coming century.  However, he states that this particular scenario "may be put aside for the moment, because no convincing model of it has been presented."

A second scenario has the WAIS gradually disintegrating and contributing to a slow sea-level rise over two centuries, followed by a more rapid disintegration over the following 50 to 200 years.  Once again, however, he notes that "progress on understanding WAIS over the past two decades has enabled us to lower the relative likelihood of [this] scenario."

In yet another scenario, the WAIS takes 500-700 years to disappear, as it raises sea-level by 60-120 cm per century.  Oppenheimer assesses the relative likelihood of this scenario to be the highest of all, "but with low confidence," as he puts it.

The last of the four scenarios concerns what occurs if ice streams slow as a result of internal ice sheet readjustments and the discharge of grounded ice decreases, which could well happen, even if ice shelves thin and major fast-moving glaciers do not slow.  In this case, he notes, "the Antarctic contribution to sea-level rise turns increasingly negative," i.e., sea level falls.

Commenting on this suite of scenarios, Oppenheimer emphatically states "it is not possible to place high confidence in any specific prediction about the future of WAIS."  It can be confidently stated, however, that there are no real-world data that suggest anything drastic is about to happen anytime soon.

A case in point is the study of Wingham et al. (1998), who used satellite radar altimeter measurements from 1992 to 1996 to estimate the rate of change of the thickness of nearly two-thirds of the grounded portion of the Antarctic Ice Sheet, as well as snowfall variability data obtained from ice cores to calculate the mass balance of the interior of the continental ice sheet over the past century.  Their results showed that, at most, the interior of the Antarctic Ice Sheet was "only a modest source or sink of sea-level mass this century," leading them to conclude that "a large century-scale imbalance for the Antarctic interior is unlikely," in harmony with a sizeable body of relative sea-level and geodetic evidence "supporting the notion that the grounded ice has been in balance at the millennial scale."

It would thus appear that the great non-floating portion of the Antarctic Ice Sheet is largely impervious to climate changes of the magnitude that produced the Medieval Warm Period and Little Ice Age, which is the type of climate change most likely to occur -- if there is any change at all -- in response to the ongoing rise in the air's CO2 content, or, if one prefers (as we do), in response to the historical cyclical behavior of solar activity that is likely responsible for the millennial-scale oscillation of climate that periodically brings us these several-hundred-year warm and cold periods.  Hence, it would also thus appear that such a climate fluctuation would have little impact on sea level.

References
Anderson, J.B. and Andrews, J.T.  1999.  Radiocarbon constraints on ice sheet advance and retreat in the Weddell Sea, Antarctica.  Geology 27: 179-182.

Bindschadler, R.  1998.  Future of the West Antarctic Ice Sheet.  Science 282: 428-429.

Oppenheimer, M.  1998.  Global warming and the stability of the West Antarctic Ice Sheet.  Nature 393: 325-332.

Wingham, D.J., Ridout, A.J., Scharroo, R., Arthern, R.J. and Shum, C.K.  1998.  Antarctic elevation change from 1992 to 1996.  Science 282: 456-458.