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

series span multiple decades; fluxes are available at high frequency; and implied ocean heat transports are consistent with estimates based on ocean measurements. In this paper, we use the CORE heat and freshwater fluxes to evaluate the mean state, variability, and trends of the air–sea fluxes in an ensemble of twentieth-century (20C) simulations of the CCSM version 4 (CCSM4) in response to specified GHG emissions. Mean air–sea heat and freshwater flux fields and the ensemble spread are examined, so

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Samantha Stevenson, Baylor Fox-Kemper, Markus Jochum, Richard Neale, Clara Deser, and Gerald Meehl

that it may not be possible to provide a definite answer that is relevant on the societal time horizon. It has been previously established ( Wittenberg 2009 ; Stevenson et al. 2010 ) that averaging over several hundred years of model output is required to obtain stable ENSO statistics, under equilibrated background conditions. Over shorter intervals, changes due to natural decadal variability may be substantial, with variance changing by a factor of 2 or more ( Wittenberg 2009 ; Stevenson et al

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Wilbert Weijer, Bernadette M. Sloyan, Mathew E. Maltrud, Nicole Jeffery, Matthew W. Hecht, Corinne A. Hartin, Erik van Sebille, Ilana Wainer, and Laura Landrum

affects decadal variability in Atlantic overturning circulation . Nature , 456 , 489 – 492 . Biastoch , A. , C. W. Böning , F. U. Schwarzkopf , and J. R. E. Lutjeharms , 2009 : Increase in Agulhas leakage due to poleward shift of Southern Hemisphere westerlies . Nature , 462 , 495 – 499 . Briegleb , B. , G. Danabasoglu , and W. Large , 2010 : An overflow parameterization for the ocean component of the Community Climate System Model . National Center for Atmospheric Research

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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

the smaller contribution of internal variability compared to the trend. Table 1. Least squares regression trends (%) in the sea ice extent for 1981–2005 (% decade −1 ), calculated from the satellite-derived NSIDC and bootstrap sea ice extents and the six CCSM4 ensemble simulations. The CCSM4 ensemble-mean sea ice extent trend is shown (in bold) in the last column of the table. Trends that are not significantly different from the null hypothesis of no trend with a confidence level of over 95% are

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Gretchen Keppel-Aleks, James T. Randerson, Keith Lindsay, Britton B. Stephens, J. Keith Moore, Scott C. Doney, Peter E. Thornton, Natalie M. Mahowald, Forrest M. Hoffman, Colm Sweeney, Pieter P. Tans, Paul O. Wennberg, and Steven C. Wofsy

, T. J. , and P. P. Tans , 1999 : Development of the CO 2 latitude gradient in recent decades . Global Biogeochem. Cycles , 13 , 821 – 826 . Conway , T. J. , P. P. Tans , L. S. Waterman , and K. W. Thoning , 1994 : Evidence for interannual variability of the carbon cycle from the National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory global air sampling network . J. Geophys. Res. , 99 , 22 831 – 22 855 . Coumou , D. , and S

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Aneesh C. Subramanian, Markus Jochum, Arthur J. Miller, Raghu Murtugudde, Richard B. Neale, and Duane E. Waliser

relationship between the Indian monsoon rainfall and ENSO . Geophys. Res. Lett. , 28 , 4499 – 4502 . Bechtold , P. , M. Köhler , T. Jung , F. Doblas-Reyes , M. Leutbecher , M. J. Rodwell , F. Vitart , and G. Balsamo , 2008 : Advances in simulating atmospheric variability with the ECMWF model: From synoptic to decadal time-scales . Quart. J. Roy. Meteor. Soc. , 134 , 1337 – 1351 . Behera , S. , R. Krishnan , and T. Yamagata , 1999 : Unusual ocean-atmosphere conditions

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C. Kendra Gotangco Castillo, Samuel Levis, and Peter Thornton

2 fertilization and climate variability . Global Biogeochem. Cycles , 21 , GB4018 , doi:10.1029/2006GB002868 . Wang , G. , E. A. B. Eltahir , J. A. Foley , D. Pollard , and S. Levis , 2004 : Decadal variability of rainfall in the Sahel: Results from a coupled GENESIS-IBIS atmosphere-biosphere model . Climate Dyn. , 22 , 625 – 637 . Yang , W. , and Coauthors , 2006 : MODIS leaf area index products: From validation to algorithm improvement . IEEE Trans. Geosci. Remote

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Synte Peacock

that anomalously cold or warm years in the model and data line are synchronous. However, it is desirable that the magnitude of the observed variability be captured by the model. When the individual ensemble members are considered, members can indeed be found that give a far better match with observational data than does the model ensemble mean. The dips seen in Fig. 3 for the individual ensemble members suggest that it is possible that there may be times over the next decade or so when the

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Alicia R. Karspeck, Steve Yeager, Gokhan Danabasoglu, Tim Hoar, Nancy Collins, Kevin Raeder, Jeffrey Anderson, and Joseph Tribbia

time-mean bias and the second term is the contribution from the time-varying component of the squared forecast misfit. Throughout the remainder of this paper, the term bias should be understood as defined in (1) : . It should be noted that these statistics are computed only for the period of the assimilation experiment. As a result, decadal-scale and longer variability in the forecast misfit is implicitly included in the bias term. While it would be preferable to assess time-mean bias over a

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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

was the first climate model that could maintain a stable present-day simulation without the use of flux corrections. The CCSM2 was released in 2002 ( Kiehl and Gent 2004 ), and CCSM3 was released in June 2004 ( Collins et al. 2006 ). One of the worst aspects of the CCSM3 climate was the El Niño–Southern Oscillation (ENSO) period, which was dominated by variability at 2 yr, rather than the 3–7-yr period from observations. Improving ENSO was the highest priority in CCSM4 development, and a

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