• Ackley, S., , P. Wadhams, , J. Comiso, , and A. Worby, 2003: Decadal decrease of Antarctic sea ice extent inferred from whaling records revisited on the basis of historical and modern sea ice records. Polar Res., 22, 1925, doi:10.1111/j.1751-8369.2003.tb00091.x.

    • Search Google Scholar
    • Export Citation
  • Allan, R., , and T. Ansell, 2006: A new globally complete monthly historical gridded mean sea level pressure dataset (HadSLP2): 1850–2004. J. Climate, 19, 58165842.

    • Search Google Scholar
    • Export Citation
  • Ammann, C. M., , G. A. Meehl, , W. M. Washington, , and C. Zender, 2003: A monthly and latitudinally varying volcanic forcing dataset in simulations of 20th century climate. Geophys. Res. Lett., 30, 1657, doi:10.1029/2003GL016875.

    • Search Google Scholar
    • Export Citation
  • Arblaster, J. M., , and G. A. Meehl, 2006: Contributions of external forcings to southern annular mode trends. J. Climate, 19, 28962905.

    • Search Google Scholar
    • Export Citation
  • Arrigo, K. R., , G. L. van Dijken, , and S. Bushinsky, 2008: Primary production in the Southern Ocean, 1997-2006. J. Geophys. Res., 113, C08004, doi:10.1029/2007JC004551.

    • Search Google Scholar
    • Export Citation
  • Bates, S. C., , B. Fox-Kemper, , S. R. Jayne, , W. G. Large, , S. Stevenson, , and S. G. Yeager, 2012: Mean biases, variability, and trends in air–sea fluxes and sea surface temperature in the CCSM4. J. Climate, in press.

    • Search Google Scholar
    • Export Citation
  • Cai, W., , and P. G. Baines, 2001: Forcing of the Antarctic circumpolar wave by El Niño–Southern Oscillation teleconnections. J. Geophys. Res., 106 (C5), 90199038.

    • Search Google Scholar
    • Export Citation
  • Cai, W., , and T. Cowan, 2007: Trends in Southern Hemisphere circulation in IPCC AR4 models over 1950–99: Ozone depletion versus greenhouse forcing. J. Climate, 20, 681693.

    • Search Google Scholar
    • Export Citation
  • Cavalieri, D. J., , and C. L. Parkinson, 2008: Antarctic sea ice variability and trends, 1979-2006. J. Geophys. Res., 113, C07004, doi:10.1029/2007JC004564.

    • Search Google Scholar
    • Export Citation
  • Collins, W. D., and Coauthors, 2006: The Community Climate System Model version 3 (CCSM3). J. Climate, 19, 21222143.

  • Comiso, J. C., 1990: DMSP SSM/I daily and monthly polar gridded bootstrap sea ice concentrations. National Snow and Ice Data Center, Boulder, CO, digital media. [Available online at http://nsidc.org/data/nsidc-0002.html.]

  • Comiso, J. C., , and F. Nishio, 2008: Trends in the sea ice cover using enhanced and compatible AMSR-E, SSM/I, and SMMR data. J. Geophys. Res., 113, C02S07, doi:10.1029/2007JC004257.

    • Search Google Scholar
    • Export Citation
  • Connolley, W. M., 2003: Long-term variation of the Antarctic circumpolar wave. J. Geophys. Res., 107, 8076, doi:10.1029/2000JC000380.

  • Curran, M. A. J., , T. D. van Ommen, , V. I. Morgan, , K. L. Phillips, , and A. S. Palmer, 2003: Ice core evidence for Antarctic sea ice decline since the 1950s. Science, 302, 12031206.

    • Search Google Scholar
    • Export Citation
  • Danabasoglu, G., , S. Bates, , B. P. Briegleb, , S. R. Jayne, , M. Jochum, , W. G. Large, , S. Peacock, , and S. G. Yeager, 2012: The CCSM4 ocean component. J. Climate, 25, 13611389.

    • Search Google Scholar
    • Export Citation
  • de la Mare, W. K., 2009: Changes in Antarctic sea-ice extent from direct historical observations and whaling records. Climatic Change, 92, 461493, doi:10.1007/s10584-008-9473-2.

    • Search Google Scholar
    • Export Citation
  • Deser, C., and Coauthors, 2012: ENSO and Pacific decadal variability in Community Climate System Model version 4. J. Climate, 25, 26222651.

    • Search Google Scholar
    • Export Citation
  • Enomoto, H., , and A. Ohmura, 1990: The influences of atmospheric half-yearly cycle on the sea ice extent in the Antarctic. J. Geophys. Res., 95 (C6), 94979511.

    • Search Google Scholar
    • Export Citation
  • Fan, K., 2007: Zonal asymmetry of the Antarctic Oscillation. Geophys. Res. Lett., 34, L02706, doi:10.1029/2006GL028045.

  • Fetterer, F., , K. Knowles, , W. Meier, , and M. Savoie, 2009: Sea ice index. National Snow and Ice Data Center, Boulder, CO, digital media. [Available online at http://nsidc.org/data/g02135.html.]

  • Fogt, R. L., , and D. H. Bromwich, 2006: Decadal variability of the ENSO teleconnection to the high-latitude South Pacific governed by coupling with the southern annular mode. J. Climate, 19, 979997.

    • Search Google Scholar
    • Export Citation
  • Gent, P. R., and Coauthors, 2011: The Community Climate System Model version 4. J. Climate, 24, 49734991.

  • Gillett, N. P., , and D. W. J. Thompson, 2003: Simulation of recent Southern Hemisphere climate change. Science, 302, 273275.

  • Gloersen, P., , and W. B. White, 2001: Reestablishing the circumpolar wave in sea ice around Antarctica from one winter to the next. J. Geophys. Res., 106 (C3), 43914395.

    • Search Google Scholar
    • Export Citation
  • Goosse, H., , W. Lefebvre, , A. de Montety, , E. Crespin, , and A. H. Orsi, 2009: Consistent past half-century trends in the atmosphere, the sea ice and the ocean at high southern latitudes. Climate Dyn., 33, 9991016, doi:10.1007/s00382-008-0500-9.

    • Search Google Scholar
    • Export Citation
  • Griffies, S. M., and Coauthors, 2009: Coordinated Ocean-Ice Reference Experiments (COREs). Ocean Modell., 26, 146, doi:10.1016/j.ocemod.2008.08.007.

    • Search Google Scholar
    • Export Citation
  • Hall, A., , and M. Visbeck, 2002: Synchronous variability in the Southern Hemisphere atmosphere, sea ice, and ocean resulting from the annular mode. J. Climate, 15, 30433057.

    • Search Google Scholar
    • Export Citation
  • Hansen, J., , R. Ruedy, , M. Sato, , and K. Lo, 2010: Global surface temperature change. Rev. Geophys., 48, RG4004, doi:10.1029/2010RG000345.

  • Harangozo, S. A., 1997: Atmospheric meridional circulation impacts on contrasting winter sea ice extent in two years in the Pacific sector of the Southern Ocean. Tellus, 49A, 388400.

    • Search Google Scholar
    • Export Citation
  • Harangozo, S. A., 2000: A search for ENSO teleconnections in the West Antarctic Peninsula climate in austral winter. Int. J. Climatol., 20, 663679.

    • Search Google Scholar
    • Export Citation
  • Harms, S., , E. Fahrbach, , and V. H. Strass, 2001: Sea ice transports in the Weddell Sea. J. Geophys. Res., 106 (C5), 90579073.

  • Holland, M. M., , and M. N. Raphael, 2006: Twentieth century simulation of the Southern Hemisphere climate in coupled models. Part II: Sea ice conditions and variability. Climate Dyn., 26, 229245, doi:10.1007/s00382-005-0087-3.

    • Search Google Scholar
    • Export Citation
  • Holland, M. M., , C. M. Bitz, , and E. C. Hunk, 2005: Mechanisms forcing an Antarctic dipole in simulated sea ice and surface ocean conditions. J. Climate, 18, 20512066.

    • Search Google Scholar
    • Export Citation
  • Holland, M. M., , D. A. Bailey, , B. P. Briegleb, , B. Light, , and E. Hunke, 2012: Improved sea ice shortwave radiation physics in CCSM4: The impact of melt ponds and aerosols on Arctic sea ice. J. Climate, 25, 14131430.

    • Search Google Scholar
    • Export Citation
  • Hunke, E. C., , and W. H. Lipscomb, 2008: CICE: The Los Alamos Sea Ice Model, documentation and software, version 4.0. Los Alamos National Laboratory Tech. Rep. LA-CC-06-012, 76 pp.

  • Hurrell, J. W., , J. J. Hack, , D. Shea, , J. M. Caron, , and J. Rosinski, 2008: A new sea surface temperature and sea ice boundary dataset for the Community Atmosphere Model 2008. J. Climate, 21, 51455153.

    • Search Google Scholar
    • Export Citation
  • Jahn, A., and Coauthors, 2012: Late-twentieth-century simulation of Arctic sea ice and ocean properties in the CCSM4. J. Climate, 25, 14311452.

    • Search Google Scholar
    • Export Citation
  • Kirkman, C. H., IV, , and C. M. Bitz, 2010: The effect of the sea ice freshwater flux on Southern Ocean temperatures in CCSM3: Deep-ocean warming and delayed surface warming. J. Climate, 24, 22242237.

    • Search Google Scholar
    • Export Citation
  • Lamarque, J.-F., and Coauthors, 2010: Historical (1850-2000) gridded anthropogenic and biomass burning emissions of reactive gases and aerosols: Methodology and application. Atmos. Chem. Phys., 10, 70177039, doi:10.5194/acp-10-7017-2010.

    • Search Google Scholar
    • Export Citation
  • Lamarque, J.-F., , G. P. Kyle, , M. Meinshausen, , K. Riahi, , S. J. Smith, , D. P. van Vuuren, , A. Conley, , and F. Vitt, 2011: Global and regional evolution of short-lived radiatively-active gases and aerosols in the representative concentration pathways. Climatic Change, 109, 191212, doi:10.1007/s10584-011-0155-0.

    • Search Google Scholar
    • Export Citation
  • Large, W. G., , and S. G. Yeager, 2009: The global climatology of an interannually varying air-sea flux data set. Climate Dyn., 33, 341364, doi:10.1007/s00382-008-0441-3.

    • Search Google Scholar
    • Export Citation
  • Lawrence, D. M., , K. W. Oleson, , M. G. Flanner, , C. G. Fletcher, , P. J. Lawrence, , S. Levis, , S. C. Swenson, , and G. B. Bonan, 2012: The CCSM4 land simulation, 1850–2005: Assessment of surface climate and new capabilities. J. Climate, 25, 22402260.

    • Search Google Scholar
    • Export Citation
  • Lean, J., 2000: Evolution of the sun’s spectral irradiance since the Maunder Minimum. Geophys. Res. Lett., 27, 24252428.

  • Liu, J., , and J. A. Curry, 2010: Accelerated warming of the Southern Ocean and its impacts on the hydrological cycle and sea ice. Proc. Natl. Acad. Sci. USA, 107, 14 98714 992, doi:10.1073/pnas.1003336107.

    • Search Google Scholar
    • Export Citation
  • Liu, J., , X. Yuan, , D. Rind, , and D. G. Martinson, 2002: Mechanism study of the ENSO and southern high latitude climate teleconnections. Geophys. Res. Lett., 29, 1679, doi:10.1029/2002GL015143.

    • Search Google Scholar
    • Export Citation
  • Liu, J., , J. A. Curry, , and D. G. Martinson, 2004: Interpretation of recent Antarctic sea ice variability. Geophys. Res. Lett., 31, L02205, doi:10.1029/2003GL018732.

    • Search Google Scholar
    • Export Citation
  • Lo Monaco, C., , N. Metzl, , A. Poisson, , C. Brunet, , and B. Schauer, 2005: Anthropogenic CO2 in the Southern Ocean: Distribution and inventory at the Indian–Atlantic boundary (World Ocean Circulation Experiment line I6). J. Geophys. Res., 110, C06010, doi:10.1029/2004JC002643.

    • Search Google Scholar
    • Export Citation
  • Marshall, G. J., 2003: Trends in the southern annular mode from observations and reanalyses. J. Climate, 16, 41344143.

  • Marshall, G. J., 2007: Half-century seasonal relationships between the southern annular mode and Antarctic temperatures. Int. J. Climatol., 27, 373383.

    • Search Google Scholar
    • Export Citation
  • Meehl, G. A., and Coauthors, 2012: Climate system response to external forcings and climate change projections in CCSM4. J. Climate, 25, 36613683.

    • Search Google Scholar
    • Export Citation
  • Mo, K. C., 2000: Relationships between low-frequency variability in the Southern Hemisphere and sea surface temperature anomalies. J. Climate, 13, 35993610.

    • Search Google Scholar
    • Export Citation
  • Moy, C. M., , P. I. Moreno, , R. B. Dunbar, , M. R. Kaplan, , J. P. Francois, , R. Villalba, , and T. Haberzettl, 2009: Past climate variability in South America and surrounding regions. Climate Change in Southern South America during the Last Two Millennia, F. Vimeux et al., Eds., Springer, 353–393.

  • North, G. N., , T. L. Bell, , and R. F. Cahalan, 1982: Sampling errors in the estimation of empirical orthogonal functions. Mon. Wea. Rev., 110, 699706.

    • Search Google Scholar
    • Export Citation
  • Parkinson, C. L., 2002: Trends in the length of the Southern Ocean sea-ice season, 1979-99. Ann. Glaciol., 34, 435440.

  • Perlwitz, J., , S. Pawson, , R. L. Fogt, , J. E. Nielsen, , and W. D. Neff, 2008: Impact of stratospheric ozone hole recovery on Antarctic climate. Geophys. Res. Lett., 35, L08714, doi:10.1029/2008GL033317.

    • Search Google Scholar
    • Export Citation
  • Peterson, R. G., , and W. B. White, 1998: Slow oceanic teleconnections linking the Antarctic circumpolar wave with the tropical El Niño–Southern Oscillation. J. Geophys. Res., 103 (C11), 24 57324 583.

    • Search Google Scholar
    • Export Citation
  • Raphael, M. N., , and M. M. Holland, 2006: Twentieth century simulation of the Southern Hemisphere climate in coupled models. Part 1: Large scale circulation variability. Climate Dyn., 26, 217228, doi:10.1007/s00382-005-0082-8.

    • Search Google Scholar
    • Export Citation
  • Rayner, N. A., , D. E. Parker, , E. B. Horton, , C. K. Folland, , L. V. Alexander, , D. P. Rowell, , E. C. Kent, , and A. Kaplan, 2003: Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century. J. Geophys. Res., 108, 4407, doi:10.1029/2002JD002670.

    • Search Google Scholar
    • Export Citation
  • Reynolds, R. W., , N. A. Rayner, , T. M. Smith, , D. C. Stokes, , and W. Q. Wang, 2002: An improved in situ and satellite SST analysis for climate. J. Climate, 15, 16091625.

    • Search Google Scholar
    • Export Citation
  • Schneider, D. P., , E. J. Steig, , and J. C. Comiso, 2004: Recent climate variability in Antarctica from satellite-derived temperature data. J. Climate, 17, 15691583.

    • Search Google Scholar
    • Export Citation
  • Schneider, D. P., , C. Deser, , and Y. Okumura, 2011: An assessment and interpretation of the observed warming of West Antarctica in the austral spring. Climate Dyn., 38, 323347, doi:10.1007/s00382-010-0985-x.

    • Search Google Scholar
    • Export Citation
  • Sen Gupta, A., , and M. H. England, 2006: Coupled ocean–atmosphere–ice response to variations in the southern annular mode. J. Climate, 19, 44574486.

    • Search Google Scholar
    • Export Citation
  • Shields, C. A., , D. A. Bailey, , G. Danabasoglu, , M. Jochum, , J. T. Kiehl, , S. Levis, , and S. Park, 2012: The low-resolution CCSM4. J. Climate, 25, 39934014.

    • Search Google Scholar
    • Export Citation
  • Shindell, D. T., , and G. A. Schmidt, 2004: Southern Hemisphere climate response to ozone changes and greenhouse gas increases. Geophys. Res. Lett., 31, L18209, doi:10.1029/2004GL020724.

    • Search Google Scholar
    • Export Citation
  • Sigmond, M., , and J. C. Fyfe, 2010: Has the ozone hole contributed to increased Antarctic sea ice extent? Geophys. Res. Lett., 37, L18502, doi:10.1029/2010GL044301.

    • Search Google Scholar
    • Export Citation
  • Simmonds, I., 2003: Modes of atmospheric variability over the Southern Ocean. J. Geophys. Res., 108, 8078, doi:10.1029/2000JC000542.

  • Simmonds, I., , and T. H. Jacka, 1995: Relationships between the interannual variability of Antarctic sea ice and the Southern Oscillation. J. Climate, 8, 637647.

    • Search Google Scholar
    • Export Citation
  • Simmonds, I., , A. Rafter, , T. Cowan, , A. B. Watkins, , and K. Keay, 2005: Large-scale vertical momentum, kinetic energy, and moisture fluxes in the Antarctic sea ice region. Bound.-Layer Meteor., 117, 149177, doi:10.1007/s10546-004-5939-6.

    • Search Google Scholar
    • Export Citation
  • Smith, R. D., and Coauthors, 2010: The Parallel Ocean Program (POP) reference manual. Los Alamos National Laboratory Tech. Rep. LAUR-10-01853, 140 pp.

  • Smith, W. O., , and D. M. Nelson, 1985: Phytoplankton bloom produced by a receding ice edge in the Ross Sea: Spatial coherence with the density field. Science, 227, 163166, doi:10.1126/science.227.4683.163.

    • Search Google Scholar
    • Export Citation
  • Stammerjohn, S. E., , M. R. Drinkwater, , R. C. Smith, , and X. Liu, 2003: Ice-atmosphere interactions during sea-ice advance and retreat in the western Antarctic Peninsula region. J. Geophys. Res., 108, 3329, doi:10.1029/2002JC001543.

    • Search Google Scholar
    • Export Citation
  • Stammerjohn, S. E., , D. G. Martinson, , R. C. Smith, , X. Yuan, , and D. Rind, 2008: Trends in Antarctic annual sea ice retreat and advance and their relation to El Niño–Southern Oscillation and southern annular mode variability. J. Geophys. Res., 113, C03S90, doi:10.1029/2007JC004269.

    • Search Google Scholar
    • Export Citation
  • Takahashi, T., and Coauthors, 2002: Global sea-air CO2 flux based on climatological surface ocean pCO2, and seasonal biological and temperature effects. Deep-Sea Res. II, 49 (9–10), 16011622, doi:10.1016/S0967-0645(02)00003-6.

    • Search Google Scholar
    • Export Citation
  • Thompson, D. W. J., , and J. M. Wallace, 2000: Annular modes in the extratropical circulation. Part I: Month-to-month variability. J. Climate, 13, 10001016.

    • Search Google Scholar
    • Export Citation
  • Thompson, D. W. J., , and S. Solomon, 2002: Interpretation of recent Southern Hemisphere climate change. Science, 296, 895899.

  • Thorndike, A. S., , D. A. Rothrock, , G. A. Maykut, , and R. Colony, 1975: The thickness distribution of sea ice. J. Geophys. Res., 80 (33), 45014513.

    • Search Google Scholar
    • Export Citation
  • Turner, J., and Coauthors, 2004: The SCAR READER project: Toward a high-quality database of mean Antarctic meteorological observations. J. Climate, 17, 28902898.

    • Search Google Scholar
    • Export Citation
  • Turner, J., and Coauthors, 2005: Antarctic climate change during the last 50 years. Int. J. Climatol., 25, 279294.

  • Turner, J., and Coauthors, 2009: Non-annular atmospheric circulation change induced by stratospheric ozone depletion and its role in the recent increase of Antarctic sea ice extent. Geophys. Res. Lett., 36, L08502, doi:10.1029/2009GL037524.

    • Search Google Scholar
    • Export Citation
  • van Loon, H., 1967: The half-yearly oscillations in middle and high southern latitudes and the coreless winter. J. Atmos. Sci., 24, 472486.

    • Search Google Scholar
    • Export Citation
  • Vavrus, S., , and D. Waliser, 2008: An improved parameterization for simulating Arctic cloud amount in the CCSM3 climate model. J. Climate, 21, 56735687.

    • Search Google Scholar
    • Export Citation
  • Wang, Y.-M., , J. L. Lean, , and N. R. Sheeley Jr., 2005: Modeling the sun’s magnetic field and irradiance since 1713. Astrophys. J., 625, 522538.

    • Search Google Scholar
    • Export Citation
  • Weijer, W., and Coauthors, 2012: The Southern Ocean and its climate in CCSM4. J. Climate, 25, 26522675.

  • White, W. B., , and R. G. Peterson, 1996: An Antarctic circumpolar wave in surface pressure, temperature, and sea-ice extent. Nature, 380, 699702.

    • Search Google Scholar
    • Export Citation
  • White, W. B., , and I. Simmonds, 2006: Sea surface temperature-induced cyclogenesis in the Antarctic circumpolar wave. J. Geophys. Res., 111, C08011, doi:10.1029/2004JC002395.

    • Search Google Scholar
    • Export Citation
  • Yuan, X., 2004: ENSO-related impacts on Antarctic sea ice: A synthesis of phenomenon and mechanisms. Antarct. Sci., 16, 415425.

  • Yuan, X., , and D. G. Martinson, 2000: Antarctic sea ice extent variability and its global connectivity. J. Climate, 13, 16971717.

  • Yuan, X., , and D. G. Martinson, 2001: The Antarctic dipole and its predictability. Geophys. Res. Lett., 28, 36093612.

  • Yuan, X., , and C. Li, 2008: Climate modes in southern high latitudes and their impacts on Antarctic sea ice. J. Geophys. Res., 113, C06S91, doi:10.1029/2006JC004067.

    • Search Google Scholar
    • Export Citation
  • Zhang, J., 2007: Increasing Antarctic sea ice under warming atmospheric and oceanic conditions. J. Climate, 20, 25152529.

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Antarctic Sea Ice Climatology, Variability, and Late Twentieth-Century Change in CCSM4

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  • 1 National Center for Atmospheric Research, Boulder, Colorado
  • | 2 Los Alamos National Laboratory, Los Alamos, New Mexico
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Abstract

A preindustrial control run and an ensemble of twentieth-century integrations of the Community Climate System Model, version 4 (CCSM4), are evaluated for Antarctic sea ice climatology, modes of variability, trends, and covariance with related physical variables such as surface temperature and sea level pressure. Compared to observations, the mean ice cover is too extensive in all months. This is in part related to excessively strong westerly winds over ~50°–60°S, which drive a large equatorward meridional ice transport and enhanced ice growth near the continent and also connected with a cold bias in the Southern Ocean. In spite of these biases in the climatology, the model’s sea ice variability compares well to observations. The leading mode of austral winter sea ice concentration exhibits a dipole structure with anomalies of opposite sign in the Atlantic and Pacific sectors. Both the El Niño–Southern Oscillation and the southern annular mode (SAM) project onto this mode. In twentieth-century integrations, Antarctic sea ice area exhibits significant decreasing annual trends in all six ensemble members from 1950 to 2005, in apparent contrast to observations that suggest a modest ice area increase since 1979. Two ensemble members show insignificant changes when restricted to 1979–2005. The ensemble mean shows a significant increase in the austral summer SAM index over 1960–2005 and 1979–2005 that compares well with the observed SAM trend. However, Antarctic warming and sea ice loss in the model are closely connected to each other and not to the trend in the SAM.

Corresponding author address: L. Landrum, P.O. Box 3000, Boulder, CO 80307. E-mail: landrum@ucar.edu

This article is included in the CCSM4 Special Collection.

Abstract

A preindustrial control run and an ensemble of twentieth-century integrations of the Community Climate System Model, version 4 (CCSM4), are evaluated for Antarctic sea ice climatology, modes of variability, trends, and covariance with related physical variables such as surface temperature and sea level pressure. Compared to observations, the mean ice cover is too extensive in all months. This is in part related to excessively strong westerly winds over ~50°–60°S, which drive a large equatorward meridional ice transport and enhanced ice growth near the continent and also connected with a cold bias in the Southern Ocean. In spite of these biases in the climatology, the model’s sea ice variability compares well to observations. The leading mode of austral winter sea ice concentration exhibits a dipole structure with anomalies of opposite sign in the Atlantic and Pacific sectors. Both the El Niño–Southern Oscillation and the southern annular mode (SAM) project onto this mode. In twentieth-century integrations, Antarctic sea ice area exhibits significant decreasing annual trends in all six ensemble members from 1950 to 2005, in apparent contrast to observations that suggest a modest ice area increase since 1979. Two ensemble members show insignificant changes when restricted to 1979–2005. The ensemble mean shows a significant increase in the austral summer SAM index over 1960–2005 and 1979–2005 that compares well with the observed SAM trend. However, Antarctic warming and sea ice loss in the model are closely connected to each other and not to the trend in the SAM.

Corresponding author address: L. Landrum, P.O. Box 3000, Boulder, CO 80307. E-mail: landrum@ucar.edu

This article is included in the CCSM4 Special Collection.

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