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Bjorn Stevens and Stephanie Fiedler

Stevens (2015 , hereinafter S15) used three lines of reasoning to argue that present-day effective aerosol radiative forcing is very likely less negative than −1 W m −2 . The most quantitative bound arose from the logic that if one wishes to maintain that some component of the warming in the first half of the twentieth century was anthropogenic in origin, then this bounds to have a smaller magnitude than other positive forcings over the same time period. By adopting a simple model that

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Masakazu Yoshimori and Anthony J. Broccoli

1. Introduction The effect of elevated atmospheric carbon dioxide on climate has been a focus of many climate change studies. While CO 2 is the most important radiative forcing agent between the preindustrial period and the present day, contributions of other forcing agents are not negligible (e.g., Charlson et al. 1992 ; Haywood and Boucher 2000 ; Solomon et al. 2007 ; Hansen and Sato 2001 ; NRC 2005 ). In addition, it has been shown that climate sensitivity, defined here as the global

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Masakazu Yoshimori, Julia C. Hargreaves, James D. Annan, Tokuta Yokohata, and Ayako Abe-Ouchi

climate sensitivity ( Edwards et al. 2007 ). In particular, the last glacial maximum (LGM) has received much of the attention as the forcing is relatively large and well known, and reasonably accurate quantitative reconstructions of the climate response are available. The past and future temperature changes are linked through the so-called climate sensitivity parameter λ , defined as surface temperature change Δ T s normalized by adjusted radiative forcing F ; Here the overbar denotes global

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Jae N. Lee, Drew T. Shindell, and Sultan Hameed

, 2007 ). Kodera and Shibata (2006) suggest that Indian Ocean monsoon circulation is correlated with 11-yr solar cycle via altered planetary wave fraction and stratospheric meridional circulation changes. Paleoclimate lake and marine records indicate changes on longer time scales in the regional hydrological cycle during the Holocene (to ∼10 kyr BP), even though discrepancies exist between them about the timing and nature of the changes. The dominant forcing for the Holocene is known to be the

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Paulo Ceppi, Giuseppe Zappa, Theodore G. Shepherd, and Jonathan M. Gregory

1. Introduction A well-known feature of the atmospheric circulation response to CO 2 forcing is the overall poleward shift of extratropical circulation, including the jet streams ( Kushner et al. 2001 ; Yin 2005 ; Barnes and Polvani 2013 ), the storm tracks ( Chang et al. 2012 ; Harvey et al. 2014 ), and the edge of the tropics ( Lu et al. 2007 ; Kang and Polvani 2011 ; Ceppi et al. 2013 ). This poleward shift is primarily mediated by sea surface temperature (SST) changes, as demonstrated

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C. W. Fairall, Taneil Uttal, Duane Hazen, Jeffrey Hare, Meghan F. Cronin, Nicholas Bond, and Dana E. Veron

). This paper complements two recent papers featuring analysis of the TAO buoy observations along 95° and 110°W: studies of the annual cycle of cloud radiative forcing at the surface ( Cronin et al. 2006a ) and the annual cycle of sensible and latent heat fluxes ( Cronin et al. 2006b ). The first paper found disagreements as large as 100 W m −2 between buoy radiative flux observations and NWP reanalysis values; the second paper found disagreements of the same order for latent heat flux. The

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Lauren E. Padilla, Geoffrey K. Vallis, and Clarence W. Rowley

1. Introduction The steady-state response of the global-mean, near-surface temperature to an increase in greenhouse gas concentrations (e.g., a doubling of CO 2 levels) is given, definitionally, by the equilibrium climate sensitivity (ECS), and this is evidently an unambiguous and convenient measure of the sensitivity of the climate system to external forcing. However, given the long time scales involved in bringing the ocean to equilibrium, the ECS may only be realized on a time scale of many

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Jonathan M. Winter and Elfatih A. B. Eltahir

. Each numerical experiment was initialized 1 April 1994 and allowed to spin up for 21 months. The domain was centered at 40°N, 95°W and spanned 100 points zonally, 60 points meridionally with a horizontal grid spacing of 60 km ( Fig. 2 ). The 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) dataset ( Uppala et al. 2005 ) was used to force the boundaries under the exponential relaxation of Davies and Turner (1977) . SSTs were prescribed using the National Oceanic

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Yi Song and Yongqiang Yu

1. Introduction Both atmospheric and oceanic circulations exhibit prominent fluctuations on decadal and multidecadal time scales. Despite rising concentrations of atmospheric greenhouse gases (GHGs), the global mean surface air temperature (SAT) has remained flat for the past 16 years (i.e., the recent warming hiatus; Easterling and Wehner 2009 ). This observation challenges the prevailing view that anthropogenic forcing leads to global warming. An interpretation regarding the hiatus is the

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Jian Yuan, Dennis L. Hartmann, and Robert Wood

called cloud radiative forcing (CRF), may respond to external influences on the climate system and thereby constitute a substantial climate feedback (e.g., Schneider 1972 ; Cess et al. 1996 ). The tropical climate system response to an external perturbation is an important outstanding problem, and cloud feedback still stands as a large source of uncertainty in predicting future climate ( Cess et al. 2001b ; Stephens 2005 ; Solomon et al. 2007 ). Clouds respond both to large-scale dynamical

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