A comprehensive review of polar processes and their role in the global climate system has recently been given by the Polar Group (1980). They acknowledge that the most pressing problem at the present time is the lack of ground-truth observations (particularly in winter) needed to adjust the numerical models to improve their portrayal of physical processes. To increase the data base in the polar regions, it is important to continue employing drifting buoys and automatic weather stations in the Southern Ocean and in the southern pack-ice zone. Modelling studies also need to be conducted in parallel with the observational programme, with particular attention focused on the interrelations between sea ice extent and climate. Current general circulation models are unable to simulate realistically the seasonal variation of sea ice and polar cloud cover, probably because the representation of boundary layer fluxes in the models is inadequate.
An understanding of the circulation of polar regions, and how this is related to lower latitude climate, is today more crucial than ever because of growing concern about the fragile environment of Antarctica and the prospect of ever larger numbers of people living and working on the ice. Climate studies have shown the sensitivity of high latitudes to global climate changes. For a doubling in the carbon dioxide content of the atmosphere, Washington and Meehl (1984) predicted an increase in the globally-averaged surface air temperature of approximately 2-3°C (the so-called "greenhouse effect"). At high latitudes, however, the temperature changes were much larger, with increases in excess of 10°C in winter and 5°C in summer predicted around the Antarctic coast. Such a large temperature change and the associated presumed increase in precipitation would have a significant effect on coastal ice, the coastline and ice-free areas.
The atmospheric ozone layer, which presently absorbs much of the damaging ultraviolet radiation from the sun before it can reach the surface of the Earth, also seems to be especially sensitive in polar latitudes. The chlorofluorocarbons (man-made chemicals used as aerosol propellants, refrigerants and for other industrial purposes) destroy ozone on reaching the stratosphere, and could be partly responsible for recently observed declines in global ozone concentration. There is now little doubt that these trace gases are implicated in the "ozone hole" phenomenon, which is a drastic reduction in ozone levels that occurs in the Antarctic each spring (Lindley, 1987; Bell, 1988). The ozone depletion apparently began in the late 1970s and the situation has deteriorated such that by 1987 ozone levels over the continent in October were only about 50% of the historic levels of the 1960s. Short durations of almost 100% ozone loss have been observed in narrow layers within the 12-20 km height range (Farman and Gardiner, 1987). Changing ozone levels affect the atmospheric temperature structure and consequently the wind field.
The problem of climate change in Antarctic regions is two-sided. We have mentioned how modifications of the global atmosphere (driven primarily from the industrialized countries of the Northern Hemisphere) could influence Antarctic circulation. The other side of the coin is that changes specific to the Antarctic could feed back into the ocean-atmosphere system at lower latitudes. Antarctica represents a major global heat sink which sets up the temperature gradient that drives the Southern Hemisphere atmospheric circulation. High latitude changes could therefore have far-reaching consequences on, for example, cyclone tracks over the Southern Ocean and thus the climates of Australia, New Zealand and South America. It is also possible that the polar energy balance could be affected by commercial activities that introduce oil spills or low-level air pollution.
The feedback effects from ozone losses and greenhouse warming could potentially have even more serious long-term consequences. The ozone hole itself is restricted to Antarctic (and possibly Arctic) latitudes because of the unique meteorological conditions there, but its recurrence every spring could accelerate the overall global depletion. It is estimated that a 1 % decline in global ozone levels could result in a 4-6% rise in the incidence of some skin cancers. The danger from the greenhouse warming lies in accelerating the rise in world sea level. The West Antarctic Ice Sheet is largely grounded below sea level, but is surrounded by floating ice shelves that retard the seaward progress of the outflowing ice streams. If these floating ice shelves around the continental margin were to disappear, the stability of the West Antarctic Ice Sheet would be threatened. People have speculated that the ice sheet could eventually melt and result in sea level rises of 5-6 metres or more over a period of several hundred years (e.g., Mercer, 1978).
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