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IP005: State of the Antarctic and Southern Ocean Climate System (SASOCS)

ATCM XXX and CEP X 2007, New Delhi, India

Information Paper

IP005: State of the Antarctic and Southern Ocean Climate System (SASOCS)

Summary:

This Information Paper provides a review of the key developments over the past two years in our understanding of Antarctic climate and the role of the Antarctic climate system in the global climate system. It comments on the findings of the 2007 Intergovernmental Panel on Climate Change (IPCC) that relate to the Antarctic. A follow-up paper will incorporate studies of effects of climate change on the biota.

  • Antarctica and the Southern Ocean play a major role in the Earth’s climate system. They are being and will continue to be affected by global climate change. Their responses to such change will have significant impact on global conditions, especially sea level.
  • Modern climate in the region results from the interplay of the ice sheet – ocean – sea ice – atmosphere system and its response to past and present climate forcing.
  • Superimposed on the long-term trend of post-glacial warming are millennial and finer scale oscillations whose causes are not well understood aside from those associated with the 11-year sunspot cycle.
  • In the past 50 years unprecedented climatic changes cut across these trends. They include the near- surface atmospheric warming observed on the west of the Antarctic Peninsula, with associated rapid warming of the surface ocean, retreat of glaciers and the collapse of ice shelves around the Antarctic Peninsula.
  • While ice is being lost from glaciers in the Peninsula and in West Antarctica, East Antarctica shows much less ice loss.
  • Consistent with global warming, the Antarctic troposphere has warmed while the stratosphere has cooled. Part of the reason for stratospheric cooling is ozone depletion.
  • Cooling of the stratosphere appears to have encouraged the development of polar stratospheric clouds, which may have exacerbated ozone depletion.
  • The atmospheric pressure gradient between mid latitudes and Antarctica has steepened over the past 50 years, intensifying the westerlies over the Southern Ocean, and warming the Antarctic Peninsula; this change in pressure and wind has had no significant effect as yet on temperature in East Antarctica, which remains cool.
  • The upper kilometer of the circumpolar Southern Ocean has warmed, as have the densest components of Antarctic Bottom Water in the Weddell Sea.
  • The coastal ocean has freshened between the Ross Sea and the Southern Indian Ocean, making the Antarctic Bottom Water formed there less saline.
  • Since the early 1970s sea ice has reduced west of the Antarctic Peninsula, and in the Weddell Sea. These decreases are balanced by an increase in the Ross Sea.
  • Projections of Antarctic climate change over the 21st century with a doubling of CO2 in the atmosphere indicate warming of the sea ice zone; a reduction in sea ice extent; and warming of the Antarctic interior, accompanied by increased snowfall.
  • Climate models need further development to forecast change at the regional level.
  • The retreat of the Antarctic ice sheet since the Last Glacial Maximum could be significantly accelerated by global warming. Ice sheet models are not yet adequate to answer pressing questions about the effect of warming on ice melt and sea level. This topic requires significant research.
  • Threshold effects may have a significant impact on the ice sheet and sea ice extent. During the last glacial and current interglacial, such effects resulted in massive reorganizations of the ocean-atmosphere- cryosphere system, leading to rapid climate change events. Comprehensive sampling and modeling of the ocean-ice-atmosphere system in the region is needed to forecast such events with confidence.

The paper is a summary of a detailed review produced for submission to a scientific journal. by the SCAR Scientific Research Programme on Antarctica and the Global Climate System (S. Aoki, P.J. Barrett, N.A.N. Bertler, T. Bracegirdle, D. Bromwich, H. Campbell, G. Casassa, A. N. Garabato, W.B. Lyons, K.A. Maasch, P.A. Mayewski, M.P. Meredith, C. Summerhayes, J. Turner, D. Vaughan, A. Worby, and C. Xiao), For access to the original paper please contact the SCAR Secretariat.

ATCM - Antarctic Treaty Consultative Meeting
CEP - Committee for Environmental Protection
30th Antarctic Treaty Consultative Meeting
30 Apr 2007 - 11 May 2007