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Andrew R. Friedman, Gabriele C. Hegerl, Andrew P. Schurer, Shih-Yu Lee, Wenwen Kong, Wei Cheng, and John C. H. Chiang

thick blue line indicates the multimodel ensemble mean. Anthropogenic aerosol forcing also remains a large uncertainty in the multimodel mean anthropogenic fingerprint. Although all models examined except BCC-CSM1.1 do contain some representation of sulfate aerosol indirect effects, intermodel differences in aerosol parameterization result in different magnitudes and spatial patterns of aerosol forcing ( Ekman 2014 ; Guo et al. 2015 ; Allen et al. 2015 ; Rotstayn et al. 2015 ), particularly

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Intan S. Nurhati, Kim M. Cobb, and Emanuele Di Lorenzo

1. Introduction The detection of anthropogenic climate trends in the tropical Pacific is complicated by prominent interannual and decadal-scale natural climate variations in the region. Global temperature and precipitation patterns are heavily impacted by the interannual (2–7 yr) El Niño–Southern Oscillation (ENSO) phenomenon in the tropical Pacific, whose warm extremes are characterized by positive sea surface temperature and precipitation anomalies in the eastern and central tropical Pacific

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Bruce T. Anderson, Jeff R. Knight, Mark A. Ringer, Jin-Ho Yoon, and Annalisa Cherchi

extreme precipitation ( Zhang et al. 2007 ; Min et al. 2009 ); atmospheric humidity ( Santer et al. 2007 ; Willett et al. 2010 ); and streamflow ( Hidalgo et al. 2009 )—are consistent with increased anthropogenic emissions of greenhouse gases and aerosols and inconsistent with other known forcing agents, including solar and volcanic activity ( Barnett et al. 2005 ; Solomon et al. 2007 ). However, such consistency does not preclude the possible influence of other unknown forcing agents ( Stone et al

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Gareth S. Jones and John J. Kennedy

1. Introduction By the first decade of the twenty-first century observed global near-surface temperatures had increased by about 0.8 K since the late nineteenth century ( Hartmann et al. 2013 ). Formal detection studies have attributed most of this warming to anthropogenic influences (e.g., Santer et al. 1995 ; Hegerl et al. 1997 ; Tett et al. 1999 ; Stott et al. 2000 ; Gillett et al. 2002 ; Braganza et al. 2004 ; Huntingford et al. 2006 ; Stott et al. 2006 ; Zhang et al. 2006 ; Stone

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Guoyu Ren, Jiao Li, Yuyu Ren, Ziying Chu, Aiying Zhang, Yaqing Zhou, Lei Zhang, Yuan Zhang, and Tao Bian

centralized heating (summer air conditioning) in the north (south) and other anthropogenic factors ( Zhang et al. 2010 ; Ren and Zhou 2014 ); and the larger proportion of stations with negative urbanization effects that was found in the arid northwest China region, especially in the northern Xinjiang Autonomous Region during summer, which was mostly likely caused by the oasisization accompanied by the expansion of built-up areas in the cities throughout the desert region ( Zhang et al. 2010 ; Ren and

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Stacey Kawecki, Geoffrey M. Henebry, and Allison L. Steiner

. 2006 ). We include the direct and indirect radiative effects of aerosols with anthropogenic emissions and online chemistry to predict CN. In this version of the model, the chemistry module calculates the number and mass of aerosols that will activate as CCN based on hygroscopicity and supersaturation (Köhler curves), and provides this prognostic CCN to the microphysics module. Gas-phase chemistry is simulated with the Regional Acid Deposition Model, version 2, (RADM2) chemical mechanism ( Stockwell

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Cheng Qian and Xuebin Zhang

). CMIP5 includes the latest generation of climate models, with an ability to simulate surface temperature that has improved in many aspects relative to the previous generation of models (CMIP3; Flato et al. 2013 ). We consider the effects of individual external forcings as well as the combined effect of multiple external forcings. The forcings under consideration include natural external forcing and anthropogenic forcing (greenhouse gas and anthropogenic aerosol concentrations and land-use change

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Anna Katavouta, Richard G. Williams, and Philip Goodwin

meridional overturning, and (iv) the extent of Southern Ocean mode water formation. To address these questions, we take a step back from the complex Earth system models and conduct sensitivity experiment using idealized atmosphere–ocean models so as to provide a clearer mechanistic connection between the effects of different processes contributing to ventilation and the TCRE. Since observational reconstructions reveal enhanced uptake of anthropogenic heat and carbon in the upper thermocline over the

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Thomas L. Delworth, Fanrong Zeng, Anthony Rosati, Gabriel A. Vecchi, and Andrew T. Wittenberg

and their association with decadal changes in local sea surface temperature. There are a number of factors that could have contributed to the recent observed hiatus in global warming ( Clement and DiNezio 2014 ), including natural radiative forcing, anthropogenic radiative forcing, and internal variability of the climate system. Potential natural radiative forcing factors include volcanic activity ( Santer et al. 2014 ) and a persistently low level of solar irradiance in the most recent solar

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Nicholas P. Klingaman, Jason Butke, Daniel J. Leathers, Kevin R. Brinson, and Elsa Nickl

the subsequent reduction in precipitation would, in turn, cause a decrease in evapotranspiration. If allowed to continue unabated, such a feedback could produce local-scale drought conditions. On the other hand, if the increase in moisture convergence dominated the reduction in evapotranspiration, then the resultant negative feedback on moisture availability could mitigate the effects of local deforestation. Although this issue has been examined in the tropics (e.g., Henderson-Sellers et al. 1993

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