Antarctic Sea Ice and Climate
The Antarctic sea ice zone remains one of the least known regions of the earth's surface. Apart from satellite derived data on ice extent and concentration, there are few reasonable climatological estimates of ice conditions that can be used for validation of numerical models. What limited information we have, mostly from the Weddell Sea, indicates that the ice characteristics and the dominant processes in the Antarctic are substantially different from those in the central Arctic. The Antarctic sea ice zone acts as a regional boundary between the Antarctic and sub Antarctic, an interface between the upper ocean and the lower atmosphere, and globally, as a region of important interactive physical and biogeochemical processes.
Uncertainties in, and the importance of, the role of sea ice in the climate system are highlighted in a US Global Change Program Report, Forum on Global Change Modeling. On the basis of studies of past climates, which provide evidence for polar amplification of warming it is predicted that under any future global warming scenario, Northern Hemisphere sea ice will probably be reduced, but that projected changes and their timing in the Southern Hemisphere sea ice extent are less certain. Current coupled model studies of an increased carbon dioxide atmosphere are also essentially in conflict in their predicted Southern Hemisphere sea ice response. First simulations with a coupled model even suggested an expansion, but more likely thickening, of the ice cover in particular regions. Other model studies, using different parameterisations of both fluxes and sea ice processes suggest the opposite effect; that instead sea ice extent and thickness will both be drastically reduced in increased atmospheric carbon dioxide scenarios. Through ice-albedo feedback, these latter simulations also suggest that the sea ice retreat itself accounts for a significant fraction (40%) of the global atmospheric warming that will occur under CO2 doubling, with of course very large increases in the regions more local to the present day ice cover. These projected changes are at present currently impossible to ascertain, because without knowledge of the Antarctic sea ice thickness distribution, it is difficult to provide compelling evidence if and when change occurs. Since the models currently give contradictory results, it suggests that the model parameterisations of sea ice physical processes are different and some, perhaps all, of the models are unrepresentative in some way in their depiction of the sea ice cover. Without present-day knowledge of the ice thickness distribution, models however cannot be verified, so we cannot even ascertain which model physics, if any, are correct.
The role of sea ice in the global climate system has been long recognised and included as a study component of major international weather and climate programs such as the Polar Sub-Programme of the Global Atmospheric Research Programme, and the World Climate Research Programme. However several factors have restricted implementation of a co-ordinated Antarctic sea ice zone program before the present. Many of the SCAR countries, tied also through the closely associated Council of Managers of National Antarctic Programmes (COMNAP), are already carrying out, and plan to continue, sea ice zone research in both physical and biological sciences within National programs: substantial new information is now available, particularly from the Weddell Sea, Amundsen and Bellingshausen Seas, and the Indian Ocean sector. A number of sophisticated, ice-capable research vessels are now working in the Antarctic, and at the same time the increased number of nations working in the Antarctic has seen a growth in all types of shipping activity. And new remote sensing capabilities, particularly active radar systems, have greatly enhanced sea ice observation from space.