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Vanda Salgueiro, Maria João Costa, Ana Maria Silva, and Daniele Bortoli

and at the top of the atmosphere (TOA) ( Dong et al. 2006 ). A way of quantifying the cloud radiation effects at the surface and at the TOA is the cloud radiative forcing (CRF), which is defined as an instantaneous change in net total radiation (SW plus LW; in W m −2 ) obtained under cloudy conditions and its clear-sky counterpart; CRF can produce a cooling (negative CRF) or a warming (positive CRF) effect on the earth–atmosphere system. CRF has been a research topic over the last decades because

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Minghong Zhang and Yi Huang

1. Introduction In the analysis of climate sensitivity, it is a convention to consider radiative forcing to comprise both instantaneous forcing that is due to perturbation in radiative gases (e.g., CO 2 ) and contributions by rapid adjustments of other atmospheric components that are not related to surface temperature change ( Ramaswamy et al. 2001 ). For instance, stratospheric temperature adjustment resulting from the radiative cooling effect of CO 2 is usually considered part of the CO 2

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Bjorn Stevens

Following the notation introduced by Stevens (2015 , hereafter S15) I denote the anthropogenic aerosol forcing by and globally averaged SO 2 emissions by where t denotes time, measured in years. For the sake of argument, assume that both aerosol–cloud and aerosol–radiation interactions contribute to forcings that scale linearly with , as advocated by Kretzschmar et al. (2017) , and also Booth et al. (2018) . In this case, By requiring the forced (globally averaged) temperature

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Nicholas Lewis and Judith Curry

1. Introduction There has been considerable scientific investigation of the magnitude of the warming of Earth’s climate from changes in atmospheric carbon dioxide (CO 2 ) concentration. Two standard metrics summarize the sensitivity of global surface temperature to an externally imposed radiative forcing. Equilibrium climate sensitivity (ECS) represents the equilibrium change in surface temperature to a doubling of atmospheric CO 2 concentration. Transient climate response (TCR), a shorter

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K. E. Taylor, M. Crucifix, P. Braconnot, C. D. Hewitt, C. Doutriaux, A. J. Broccoli, J. F. B. Mitchell, and M. J. Webb

temperature change. The radiative “forcing” of the system is commonly quantified in terms of the immediate impact of any imposed change on the TOA fluxes. 1 An imposed increase in CO 2 concentration, for example, promptly reduces, by a small amount, the longwave radiation emanating to space and is therefore considered a radiative forcing. The radiative imbalance caused by this forcing tends to warm the system and, in any given model, the global mean temperature response is roughly proportional to the

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Ben Kravitz, Douglas G. MacMartin, Philip J. Rasch, and Andrew J. Jarvis

1. Introduction One of the cornerstone problems in climate science is understanding the climate system’s response to changes in climate forcing agents, such as the concentration of CO 2 and other greenhouse gases, total solar irradiance, and different types of aerosols. For example, formulating any climate target or emissions path requires knowledge of how to compare the effects of different greenhouse gases with different radiative properties and atmospheric lifetimes ( Fuglestvedt et al

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Eui-Seok Chung and Brian J. Soden

1. Introduction Climate feedbacks amplify or dampen the initial radiative perturbation induced by a forcing agent through changes in climate variables in response to global-mean surface temperature change. Intermodel differences in climate feedbacks are widely accepted as the primary cause for intermodel spread in the projected future climate changes in response to imposed radiative forcings (e.g., Cess et al. 1990 ; Zhang et al. 1994 ; Colman 2003 ; Bony et al. 2006 ). However, model

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Maria A. A. Rugenstein, Jonathan M. Gregory, Nathalie Schaller, Jan Sedláček, and Reto Knutti

1. Introduction and tropospheric adjustment The response of the global energy budget to an external perturbation of the energy content can be described by the heat uptake of ocean, ice, and land ( N ), the perturbation or radiative forcing ( F ), and the feedback response ( λT ), with the climate feedback parameter λ and temperature anomaly T : with the heat capacity of the climate system, C . Changes that are mediated by the climate system’s response to the perturbation are called feedback

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Christopher M. Aiken and Matthew H. England

ice shields the air–sea exchange of gases, including carbon dioxide, so it fundamentally controls the rate of CO 2 uptake by the world’s oceans. The effects upon climate of freshwater forcing due to ice melt have been discussed in a number of previous studies. A decay in the AABW and Antarctic Intermediate Water (AAIW) production rates due to melting of Antarctic land ice has been suggested as a possible trigger for the Bolling–Allerod warming ( Weaver et al. 2003 ). Saenko et al. (2003

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Nadir Jeevanjee, Jacob T. Seeley, David Paynter, and Stephan Fueglistaler

1. Introduction Changes in Earth’s CO 2 greenhouse effect (i.e., CO 2 radiative forcing) have been a primary driver of past and present climate changes, and are well simulated by state-of-the-art radiation codes (e.g., Mlynczak et al. 2016 ; Pincus et al. 2015 ; Oreopoulos et al. 2012 ; Forster et al. 2011 ). While this accuracy is critical for credible climate simulation and has thus been a priority for radiation research, less emphasis has been placed on an intuitive understanding of CO

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