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S. J. Ghan, X. Liu, R. C. Easter, R. Zaveri, P. J. Rasch, J.-H. Yoon, and B. Eaton

1. Introduction Anthropogenic aerosol is thought to play an important role in driving climate change, but its role is so complex that uncertainty in estimates of radiative forcing of climate change is dominated by uncertainty associated with forcing by anthropogenic aerosol ( Forster et al. 2007 ). This complexity arises because anthropogenic aerosol alters the planetary energy balance through a variety of mechanisms operating across a wide range of spatial scales: direct effects ( Haywood and

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Gerald A. Meehl, Warren M. Washington, Julie M. Arblaster, Aixue Hu, Haiyan Teng, Claudia Tebaldi, Benjamin N. Sanderson, Jean-Francois Lamarque, Andrew Conley, Warren G. Strand, and James B. White III

. Experiments analyzed here include twentieth-century simulations (1850–2005) with a combination of anthropogenic and natural forcings ( Gent et al. 2011 ), as well as experiments run with single forcings or a subset of combinations of forcings. The anthropogenic forcings in CCSM4 include time-evolving GHGs, as well as prescribed time- and space-evolving concentrations of tropospheric ozone, stratospheric ozone, the direct effect of sulfate aerosols (there are no indirect effects from sulfate or any other

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

driven by transiently varying anthropogenic forcing between the years 1850 and 2005 (details in Gent et al. 2011 ). The twentieth-century integrations were initialized from randomly selected years near the end of a 1000-yr control run that used stationary radiative forcings corresponding to the year 1850. a. Sea ice The ice pack represents an integrative climatic variable that is closely linked with temperature, precipitation, clouds, salinity, and SLP ( Vavrus et al. 2009 ; Higgins and Cassano

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

-state balance with the preindustrial atmosphere. Anthropogenic CO 2 (C ant ) is the additional carbon absorbed by the ocean because of the atmospheric CO 2 transient. We compute fluxes and inventories of C ant by subtracting simulated fields in the control integrations (CORE1850 and CPLD1850) from those in the respective transient integrations (CORE20C and CPLD20C). The control integrations include twentieth-century climate change (see above); thus, the climate effects on C nat distributions are present

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Keith Oleson

understanding urban effects on climate and weather (e.g., as reviewed by Landsberg 1981 ; Oke 1988 ; Arnfield 2003 ; Collier 2006 ; Seto and Shepherd 2009 ). The urban heat island (UHI), a phenomenon describing the fact that urban areas are generally warmer than the surrounding rural areas was first recognized by Luke Howard in 1820 as described by Landsberg (1981) in his authoritative review of the field of urban climatology ( Oke 1991 ). The causes of the UHI were investigated in a series of

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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

1. Introduction Carbon dioxide is a dominant anthropogenic greenhouse gas in the earth's atmosphere. Its atmospheric concentration has risen from 280 ppm preindustrially to 390 ppm in 2011 because of fossil fuel combustion and land use change ( R. F. Keeling et al. 1996 ; Prentice et al. 2000 ). The extent to which CO 2 levels in the atmosphere continue increasing will be the primary determinant of future climate change ( Solomon et al. 2007 ). The trajectory of atmospheric CO 2 depends not

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Kirsten Zickfeld, Michael Eby, Andrew J. Weaver, Kaitlin Alexander, Elisabeth Crespin, Neil R. Edwards, Alexey V. Eliseev, Georg Feulner, Thierry Fichefet, Chris E. Forest, Pierre Friedlingstein, Hugues Goosse, Philip B. Holden, Fortunat Joos, Michio Kawamiya, David Kicklighter, Hendrik Kienert, Katsumi Matsumoto, Igor I. Mokhov, Erwan Monier, Steffen M. Olsen, Jens O. P. Pedersen, Mahe Perrette, Gwenaëlle Philippon-Berthier, Andy Ridgwell, Adam Schlosser, Thomas Schneider Von Deimling, Gary Shaffer, Andrei Sokolov, Renato Spahni, Marco Steinacher, Kaoru Tachiiri, Kathy S. Tokos, Masakazu Yoshimori, Ning Zeng, and Fang Zhao

mean temperature after elimination of anthropogenic CO 2 emissions is known from earlier studies with EMICs and complex ESMs ( Matthews and Caldeira 2008 ; Plattner et al. 2008 ; Eby et al. 2009 ; Solomon et al. 2009 ; Lowe et al. 2009 ; Frölicher and Joos 2010 ; Gillett et al. 2011 ; Zickfeld et al. 2012 ) and results from the cancellation of two opposing effects: the delayed warming due to ocean thermal inertia and the decrease in radiative forcing associated with declining atmospheric CO

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A. Gettelman, J. E. Kay, and K. M. Shell

1. Introduction The earth’s climate system is being perturbed by anthropogenic radiative forcing. In addition to direct radiative forcing of the system (e.g., from anthropogenic greenhouse gases), the responses to radiative forcing (surface and atmospheric temperature changes) cause feedbacks within the system that amplify or damp the changes ( Schneider 1972 ; Cess et al. 1990 ; Bony et al. 2006 ). Increases in temperature allow the specific humidity to increase, which increases the

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Samuel Levis, Gordon B. Bonan, Erik Kluzek, Peter E. Thornton, Andrew Jones, William J. Sacks, and Christopher J. Kucharik

1. Introduction Past studies indicate that managed and unmanaged terrestrial ecosystems interact with the atmosphere and other components of the earth system through a variety of biogeophysical and biogeochemical processes and characteristics. Levis (2010) reviews this topic. In the present study we consider such effects by simulating certain managed ecosystems. Managed ecosystems add to simulations of the earth system the uncertainty of human interference. Numerous climate-modeling studies

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Gerald A. Meehl, Warren M. Washington, Julie M. Arblaster, Aixue Hu, Haiyan Teng, Jennifer E. Kay, Andrew Gettelman, David M. Lawrence, Benjamin M. Sanderson, and Warren G. Strand

anthropogenic cooling effects of aerosols. Gettelman et al. (2012b) note a total indirect effect of −1.3 W m −2 in CESM1(CAM5) in 2000 compared to the preindustrial climate in 1850. Assuming this scales approximately with global AOD, this would represent an additional forcing from the indirect effect between 2006 and 2100 in CESM1(CAM5) of ~+1 W m −2 that is not present in CCSM4 since CCSM4 does not include the indirect effect. Table 1 indicates a reduction of this indirect effect in CESM1(CAM5) from

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