Earth's polar regions are typically described by climate alarmists as being reliable harbingers of global climate change, i.e., places where the first ominous signs of CO2-induced global warming should be most readily detected and quantified, claiming (as they often do) that these regions are analogous to the proverbial "canary in a coal mine." Hence, it is instructive to study what impact they may - or may not! - be having on global sea level, which is what we do here for Antarctica.
Vaughn et al. (1999) used more than 1800 published and unpublished in situ measurements of the surface mass balance of Antarctica to produce an assessment of yearly ice accumulation over the continent. Their results indicated that the "total net surface mass balance for the conterminous grounded ice sheet is 1811 Gton yr-1 (149 kg m-2 yr-1) and for the entire ice sheet including ice shelves and embedded ice rises, 2288 Gton yr-1 (166 kg m-2 yr-1)." These values, in their words, "are around 18% and 7% higher than the estimates widely adopted at present [1999]," which were derived about 15 years earlier. Hence, they suggest that net icefall on Antarctica may well have increased somewhat over that prior decade and a half. Nevertheless, because of uncertainties in the various numbers, Vaughn et al. say "we are still unable to determine even the sign of the contribution of the Antarctic Ice Sheet to recent sea level change," which suggests the Antarctic canary has not a clarity of mind on the matter and is somewhat befuddled.
In another review of the subject that was published about the same time, Reeh (1999) found a broad consensus for the conclusion that a 1°C warming would create but little net change in mean global sea level; for Greenland's contribution would be a sea level rise on the order of 0.30 to 0.77 millimeters per year, while Antarctica's contribution would be a fall on the order of 0.20 to 0.70 millimeters per year, which also suggests the Antarctic canary is rather confused.
The following year, Wild and Ohmura (2000) studied the mass balance of Antarctica using two general circulation models developed at the Max Plank Institute for Meteorology in Hamburg, Germany: the older ECHAM3 and the new and improved ECHAM4. Under a doubled atmospheric CO2 scenario, the two models were in close agreement in their mass balance projections, with both of them predicting increases in ice sheet growth, indicative of decreases in sea level, which by this time had the Antarctic canary really bewildered.
Two years later, van der Veen (2002) addressed the problem again, noting that "for purposes of formulating policies, some of which could be unpopular or costly, it is imperative that probability density functions be derived for predicted values such as sea level rise," further stating that with "greater societal relevance comes increased responsibility for geophysical modelers to demonstrate convincingly the veracity of their models to accurately predict future evolution of the earth's natural system or particular components thereof." In stepping forward to perform this task with respect to sea level change, however, he was forced to conclude that "the validity of the parameterizations used by [various] glaciological modeling studies to estimate changes in surface accumulation and ablation under changing climate conditions has not been convincingly demonstrated." Van der Veen calculated, for example, that uncertainties in model parameters are sufficiently great to yield a 95% confidence range of projected meltwater contributions from Greenland and Antarctica that encompass global sea-level lowering as well as rise by 2100 A.D. for low, middle and high warming scenarios. Hence, even for the worst of the IPCC warming projections, there could well be little to no change in mean global sea level due to the likely rise in the air's CO2 content that may occur over the rest of this century. As a result, van der Veen concludes that the confidence level that can be placed in current ice sheet mass balance models "is quite low." Paraphrasing an earlier assessment of the subject, in fact, he says that today's best models "currently reside on the lower rungs of the ladder of excellence" and that "considerable improvements are needed before accurate assessments of future sea-level change can be made," once again leaving the Antarctic canary little to do but wring its wings in frustration.
Last of all, and most recently, Wadhams and Munk (2004) attempted "an independent estimate of eustatic sea level rise based on the measured freshening of the global ocean, and with attention to the contribution from melting of sea ice (which affects freshening but not sea level)," reporting that their analysis produces "a eustatic rise of only 0.6 mm/year" and that when a steric contribution of 0.5 mm/year is added to the eustatic component, "a total of 1.1 mm/year, somewhat less than IPCC estimates," is the final result. Perhaps the most interesting finding of their analysis, however, is that the continental run-off which is "allowed," after subtracting the effect of sea ice melt, "is considerably lower than current estimates of sub-polar glacial retreat, suggesting a negative contribution from polar ice sheets (Antarctica plus Greenland) or from other non-glacial processes." In this regard, they assert "we do not have good estimates of the mass balance of the Antarctic ice sheet, which could make a much larger positive or negative [our italics] contribution."
The bottom line of Wadhams and Munk's analysis, as well as those of the other studies we have reviewed, clearly suggests - in fact states - there is considerable uncertainty associated with a number of basic parameters that are related to the water balance of the world's oceans and the meltwater contribution of Antarctica; and until these uncertainties are satisfactorily resolved, we - like the Antarctic canary - cannot be confident that we know what is happening at the bottom of the world in terms of phenomena related to the vertical displacement of the upper surface of the world's oceans. In fact, we haven't really a clue.
References
Reeh, N. 1999. Mass balance of the Greenland ice sheet: Can modern observation methods reduce the uncertainty? Geografiska Annaler 81A: 735-742.
van der Veen, C.J. 2002. Polar ice sheets and global sea level: how well can we predict the future? Global and Planetary Change 32: 165-194.
Vaughn, D.G., Bamber, J.L., Giovinetto, M., Russell, J. and Cooper, A.P.R. 1999. Reassessment of net surface mass balance in Antarctica. Journal of Climate 12: 933-946.
Wadhams, P. and Munk, W. 2004. Ocean freshening, sea level rising, sea ice melting. Geophysical Research Letters 31: 10.1029/2004GL020039.
Wild, M. and Ohmura, A. 2000. Change in mass balance of polar ice sheets and sea level from high-resolution GCM simulations of greenhouse warming. Annals of Glaciology 30: 197-203.