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Alexandra K. Jonko, Karen M. Shell, Benjamin M. Sanderson, and Gokhan Danabasoglu

1. Introduction It has been suggested that climate sensitivity, Earth’s equilibrium surface temperature response to an external perturbation, is a constant property of the climate system that remains unchanged under different forcing magnitudes and types. Indeed, several previous model studies find little to no dependence of climate sensitivity on forcing ( Chen and Ramaswamy 1996 ; Forster et al. 2000 ; Boer and Yu 2003 ; Hansen et al. 2005 ). More recent work exploring a broader range of

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Norman G. Loeb and Wenying Su

1. Introduction Radiative forcing by aerosols is identified as the largest uncertainty in anthropogenic radiative forcing of climate. Aerosols influence the radiation budget of the earth directly by scattering and absorbing solar radiation (direct radiative forcing) and indirectly by modifying the microphysical characteristics and lifetimes of clouds (indirect forcing). Recently, Forster et al. (2007) provided a review of several model- and observation-based estimates of clear-sky and all

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L. Liu, D. Shawki, A. Voulgarakis, M. Kasoar, B. H. Samset, G. Myhre, P. M. Forster, Ø. Hodnebrog, J. Sillmann, S. G. Aalbergsjø, O. Boucher, G. Faluvegi, T. Iversen, A. Kirkevåg, J.-F. Lamarque, D. Olivié, T. Richardson, D. Shindell, and T. Takemura

1. Introduction Understanding the influence that humans have on the planet through their emissions of anthropogenic greenhouse gases (GHGs) and aerosols is an important part of tackling the climate change challenge. The impact of these anthropogenic forcers on the hydrological cycle is one of the main topics in climate change research (e.g., Wu et al. 2013 ), since any changes to radiatively active constituents can mean changes in the patterns of rainfall, droughts, and storms, all of which

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Lixin Wu, Yan Sun, Jiaxu Zhang, Liping Zhang, and Shoshiro Minobe

) freshwater forcing over the western tropical Pacific decreases (increases) sea surface height locally and sets up a positive (negative) zonal pressure gradient anomaly, which accelerates (decelerates) the meridional overturning circulation and equatorial surface westward flow. This leads to an intensification (reduction) of meridional heat divergence and vertical cold advection, and thus a development of La Niña (El Niño)–like response in the tropics. The tropical responses are further substantiated by

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M. Biasutti, I. M. Held, A. H. Sobel, and A. Giannini

models (GCMs). Recently, different atmospheric GCMs ( Folland et al. 1986 ; Giannini et al. 2003 ; Tippett and Giannini 2006 ; Lu and Delworth 2005 ; Hoerling et al. 2006 ), forced with the historic time series of global sea surface temperatures (SSTs), have been able to reproduce the main outlines of the twentieth-century Sahel pluvials and droughts, thus demonstrating that oceanic forcing has been the dominant driver of rainfall variability in this region. It appears that land surface and

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Leon D. Rotstayn, Mark A. Collier, Drew T. Shindell, and Olivier Boucher

1. Introduction Aerosol effects on climate are highly uncertain; even in the global mean, effective radiative forcing (ERF) caused by anthropogenic aerosols has a 5%–95% uncertainty range of −0.1 to −1.9 W m −2 , according to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR5; Boucher et al. 2013 ). Because aerosol forcing is so uncertain, it is difficult to use observations to constrain other critical properties of the climate system, such as transient

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Robert J. Allen and Charles S. Zender

forcings ( Shindell et al. 1999 ; Feldstein 2002 ; Gong et al. 2002 ). Several such external forcings have been identified, although no dominant mechanism has been clearly established. Atmospheric general circulation model (AGCM) simulations have showed that much of the multiannual to multidecadal variability of the NAO, as well as the late-twentieth-century trend, is related to North Atlantic SSTs ( Rodwell et al. 1999 ; Robertson et al. 2000 ). AGCMs have also showed that warming of tropical SSTs

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Edmund K. M. Chang

1. Introduction It is well known that the climate of the earth is not zonally symmetric. Since the forcing at the top of the atmosphere is zonally symmetric when averaged over a day or longer, the zonal asymmetries in the earth’s climate must be forced by zonal asymmetries in the lower boundary. Zonal asymmetries in the lower boundary include asymmetries in land–ocean distribution, and asymmetries in the location of mountains. Together, these asymmetries give rise to asymmetrical distribution

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Benjamin M. Sanderson, R. Knutti, T. Aina, C. Christensen, N. Faull, D. J. Frame, W. J. Ingram, C. Piani, D. A. Stainforth, D. A. Stone, and M. R. Allen

fitting algorithm used in Stainforth et al. (2005) . b. Data preparation We seek a smooth fit to the simulated climatology and likely response to greenhouse gas forcing, both as functions of model parameters. The data required to train this emulation are taken from the first climate prediction .net ensemble of climate models, those experiments conducted with perturbed atmospheric parameters only. After filtering, an N member subset of models remains for use in this analysis (where N is 6096). The

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Richard Justin O. Small, Simon P. de Szoeke, and Shang-Ping Xie

MSD are presented in section 4 . The effect of diabatic heating anomalies on the evolution of the MSD is described in section 5 . Then section 6 investigates the relative importance of remote versus local diabatic forcing to the MSD. This is followed in section 7 by a discussion of how the present results relate to previous studies, and section 8 presents the conclusions. 2. Data and model a. Observations and reanalysis 1) Precipitation Measurements of precipitation vary greatly between

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