Sea ice is theoretically one of the most sensitive natural indicators of enhanced greenhouse warming. Any increase in the temperature of the atmosphere in the polar regions will reduce the amount of sea ice, which, in turn, will expose more of the relatively warm ocean that was previously covered by the ice pack. This warm water will further heat the atmosphere, and the cycle will continue [1].
Only recently has satellite technology enabled scientists to observe the entire Antarctic pack ice year round, and in all weather conditions. Unfortunately this means the record of observations is only short and hence it is difficult to distinguish the natural variations of the ice from any enhanced greenhouse melting. In fact, it has been suggested that it may take another decade before results are clear [2]. However, the longest studies to date have shown small, though statistically insignificant, decreases in Antarctic sea ice area [3] and sea ice extent [4]. We must be careful not to read too much into these short term results, though it would be equally unwise to dismiss them before an accurate long term record is established. A worrying indicator, however, is the significant decrease in the Arctic sea ice observed over similar periods of time [3],[5].
[1] Washington W.M. and Meehl G.A., (1989) Climate sensitivity due to increased CO2: experiments with a coupled atmosphere and ocean general circulation model. Climate Dynamics V4 1-38 [2] Barry R.G., Maslanik J.A., Steffen K., Weaver R.L., Triosi V., Cavalieri D.J. and Martin, S., (1993) Advances in Sea-Ice Research based on Remotely Sensed Passive Microwave Data. Oceanography V6 4-13 [3] Johannessen O.M., Miles M, and Bjorgo E., (1995) The Arctic's shrinking sea ice. Nature V376 126-127 (see also: http://maui.net/~jstark/fingerpr.html) [4] Simmonds I.H., Jacka T.H., (1995) Relationships between the Interannual Variability of Antarctic Sea Ice and the Southern Oscillation. Journal of Climate V8 637-647 [5] Gloersen P., and Campbell W.J., (1991) Recent variations in Arctic and Antarctic sea-ice covers. Nature V352 33-36