Summary

The recent development of remote sensing techniques and technologies for automatic data collection and transmission from the most inaccessible areas of Antarctica is greatly improving our knowledge of climate in the interior of the continent. Although much remains to be understood about the geological history, advances in geophysical techniques have allowed researchers to outline the sub-ice topography of Antarctica and reconstruct its evolution, which is linked to the amalgamation and break-up of Gondwanaland and earlier continents. The stable shield of East Antarctica is formed by a complex of Pre-cambrian cratons overlain by sedimentary rocks (Beacon Supergroup) and intruded by basaltic rocks of the Ferrar Group. West Antarctica was formed by the aggregation of several microcontinents sharing a common geological history with South America. For the purposes of this book, one of the most important features of Antarctica is its location in an expanding lithospheric plate which has been in a quite stable position with respect to the South Pole during the last 100 Ma. This means that climatic and environmental changes in this period mainly reflect global changes.

Antarctica's potential to yield mineral, coal and hydrocarbon resources such as those found in rocks of formerly contiguous continents has been the subject of much speculation in the past. Although the presence of exploitable mineral and hydrocarbon deposits is very probable, their location is largely unknown. In any case, exploitation is prohibited, at least for the near future,by a moratorium (to protect the environment) and by the severity of environmental conditions.

The dynamics of the atmosphere and oceans in the Southern Hemisphere are driven by temperatures in Antarctica, which redistribute the polar cold to lower latitudes, and replace it with warmth. A small increase in temperatures at high latitudes may be amplified by ice-albedo feedback mechanisms, with significant repercussions on the global climate system. The subsidence of cold polar air and Coriolis deflection produce an intense, clockwise polar vortex in winter, which is accompanied by high-pressure systems at the South Pole and the circumpolar flow of strong westerly winds. This vortex play an important role in the destruction of stratospheric ozone; when it disappears in the spring, there is an enhanced influx of warm, moist air masses from higher latitudes bearing persistent pollutants.

Almost all precipitation in the continent falls as snow, and East Antarctica is the largest cold desert in the world because most areas receive less than 250 mm (water equivalent) per year of snow. Although characterised by large inter-annual variability, atmospheric precipitation is much higher (up to 800 mm water equivalent) in coastal areas of West Antarctica. Under the present climatic conditions, the accumulation of snow and ice on the continent seems to roughly compensate iceberg calving and basal melting of ice shelves. Furthermore, satellite monitoring of sea-ice extent and variability in the Southern Ocean during the last 25 years has revealed no general trends. However, these conditions of relative equilibrium are expected to be significantly affected by global warming. The most recent trends in records and projections of models on global climate change indicate that the climate of Antarctica will become wetter and warmer in the 21st century.

The potential contribution of Antarctic ice sheets to the increase in global sea levels has caused general concern and interest in how the Antarctic climate may respond to increasing concentrations in greenhouse gases and other emissions produced by human activity. While some zones, such as the west coast of the Antarctic Peninsula, are already showing one of the largest warming trends in the world, East Antarctica is one of the few regions in the Southern Hemisphere experiencing a quite cold phase. Antarctic ice sheets, even those of West Antarctica (which were the most dynamic Antarctic ice sheets in the recent geological past and are grounded below sea level), are expected to scarcely contribute to global sea-level changes in the 21st century.

Although connections between the Antarctic climate, ENSO events and global atmospheric processes are only beginning to be investigated, it is now widely acknowledged that the enhanced accumulation of snow in Antarctica will contribute to a positive mass balance of Antarctic ice sheets, with a negative contribution to sea-level rise in the near future. In the longer term, the warming of waters in the Southern Hemisphere and changes to circulation will probably trigger processes which could last for millennia, long after greenhouse gas emissions have stabilised. These processes will cause basal melting of ice shelves and progressive, irreversible impacts on ice sheets, especially those of West Antarctica. The possible consequences of these long-term changes in global climate and sea levels are such that research on the Antarctic climate and its teleconnections with climate and environmental changes in the Southern Hemisphere and the rest of the world is a major priority for the 21st century.

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