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Marika M. Holland, David A. Bailey, Bruce P. Briegleb, Bonnie Light, and Elizabeth Hunke

1. Introduction Sea ice is a sensitive indicator of climate change and reductions in Arctic ice cover have been considerable over the satellite record since 1979 (e.g., Serreze et al. 2007 ). Climate models project that Arctic sea ice loss will continue into the future with the possibility of ice-free summers occurring within this century (e.g., Holland et al. 2006 ; Wang and Overland 2009 ; Boe et al. 2009 ). Accompanying this rapid sea ice loss is an amplified warming in Arctic regions (e

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Laura Landrum, Marika M. Holland, David P. Schneider, and Elizabeth Hunke

1. Introduction The Antarctic sea ice cover undergoes a large seasonal range from a climatological maximum of approximately 19 million km 2 in extent in September to a minimum of 3 million km 2 in February (e.g., Cavalieri and Parkinson 2008 ) ( Fig. 1 ). The seasonal cycle of ice advance and retreat is influenced by the dominant seasonality in the atmosphere and the semiannual oscillation (SAO)—a biannual (spring and autumn) strengthening and poleward migration of the circumpolar trough (e

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Alexandra Jahn, Kara Sterling, Marika M. Holland, Jennifer E. Kay, James A. Maslanik, Cecilia M. Bitz, David A. Bailey, Julienne Stroeve, Elizabeth C. Hunke, William H. Lipscomb, and Daniel A. Pollak

1. Introduction The Arctic Ocean has undergone substantial changes in recent decades, including warm anomalies of the Atlantic layer in the Arctic Ocean (e.g., Quadfasel et al. 1991 ; Polyakov et al. 2005 ), changes in the liquid freshwater (FW) storage in the Beaufort Gyre ( Proshutinsky et al. 2009 ; McPhee et al. 2009 ), and the well-known decrease in the summer sea ice extent (e.g., Stroeve et al. 2008 ), which has set several successive record minima during the last decade and has

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Peter R. Gent, Gokhan Danabasoglu, Leo J. Donner, Marika M. Holland, Elizabeth C. Hunke, Steve R. Jayne, David M. Lawrence, Richard B. Neale, Philip J. Rasch, Mariana Vertenstein, Patrick H. Worley, Zong-Liang Yang, and Minghua Zhang

1. Introduction The Community Climate System Model (CCSM) is a general circulation climate model consisting of atmosphere, land, ocean, and sea ice components that are linked through a coupler that exchanges state information and fluxes between the components. The CCSM is developed and used by a community of scientists and students from universities, national laboratories, and other institutions. The CCSM has been used to study several paleoclimate epochs, the climate of the more recent past

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William H. Lipscomb, Jeremy G. Fyke, Miren Vizcaíno, William J. Sacks, Jon Wolfe, Mariana Vertenstein, Anthony Craig, Erik Kluzek, and David M. Lawrence

global-mean sea level by an average of ~1 mm yr −1 . The recent ice sheet contribution to global-mean sea level rise (SLR) is comparable to the estimated contributions from ocean thermal expansion and melting of smaller glaciers and ice caps ( Church et al. 2011 ) and is likely to increase as the earth's climate warms further. Estimates of twenty-first-century ice sheet mass loss are highly uncertain. The Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4) ( Meehl et al

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Matthew C. Long, Keith Lindsay, Synte Peacock, J. Keith Moore, and Scott C. Doney

available observational data. Two configurations of CESM1 are considered: 1) the fully coupled Earth system model, including ocean, sea ice, land, and atmosphere models; and 2) the ocean-ice component models forced by atmospheric reanalysis data. Our analysis is aimed at identifying model biases and examining the model's twentieth-century mean state, seasonal cycle, interannual variability, and transient response. Furthermore, we explicitly test the degree to which the fully coupled model is able to

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Stephen J. Vavrus, Marika M. Holland, Alexandra Jahn, David A. Bailey, and Benjamin A. Blazey

1. Introduction Noticeable climate change has recently emerged in the Arctic, as evidenced by a decades-long warming trend that has triggered a number of pronounced environmental changes, including expanded vegetation, altered ecosystems, reduced spring–summer snow cover, and declining sea ice ( Stroeve et al. 2007 ; Hegseth and Sundfjord 2008 ; Bhatt et al. 2010 ; Brown et al. 2010 ). The retreat of the ice pack has been particularly dramatic during summer, culminating in the melt seasons

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Susan C. Bates, Baylor Fox-Kemper, Steven R. Jayne, William G. Large, Samantha Stevenson, and Stephen G. Yeager

used. This CORE (version 2) dataset, is described and evaluated by Large and Yeager (2009) . The CORE forcing is based largely on the vector wind, air temperature, and humidity from the National Centers for Environmental Prediction (NCEP)–National Center for Atmospheric Research (NCAR) reanalysis ( Kalnay et al. 1996 ), but it uses data from alternate sources for radiation, precipitation, and sea ice concentration as well as for the critical step of correcting mean biases. It has been used to

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C. M. Bitz, K. M. Shell, P. R. Gent, D. A. Bailey, G. Danabasoglu, K. C. Armour, M. M. Holland, and J. T. Kiehl

are rarely run long enough, and instead the ECS is usually approximated from a climate model with a mixed layer ocean model, which we call a slab-ocean model (SOM), with prescribed, annually periodic ocean heat transport. Typically the SOM is designed to reproduce observed SST and sea ice cover (e.g., McFarlane et al. 1992 ; Kiehl et al. 2006 ; Knutson 2009 ; Schmidt et al. 2006 ). However, reproducing observations rather than the mean state of the climate model with an OGCM has two

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Jennifer E. Kay, Marika M. Holland, Cecilia M. Bitz, Edward Blanchard-Wrigglesworth, Andrew Gettelman, Andrew Conley, and David Bailey

a. Description of climate model experiments This study uses a unique set of coupled climate model experiments to isolate the influence of atmospheric physics and ocean model complexity on the equilibrium Arctic climate response to 2 × CO 2 ( Table 1 ). All experiments used the same Community Climate System Model, version 4 (CCSM4) ( Gent et al. 2011 ) land, ocean, and sea ice components with one of two versions of the Community Atmosphere Model (CAM) released with Community Earth System Model

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