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Cloud-Radiative Forcing and Climate: Results from The Earth Radiation Budget Experiment

Authors:
Veerabhadran Ramanathan at University of California, San Diego
Veerabhadran Ramanathan
Robert D. Cess at Stony Brook University
Robert D. Cess
E F Harrison
E F Harrison
E F Harrison
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Patrick Minnis at Analytical Mechanics Associates, Inc.
Patrick Minnis
  • Analytical Mechanics Associates, Inc.
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The study of climate and climate change is hindered by a lack of information on the effect of clouds on the radiation balance of the earth, referred to as the cloud-radiative forcing. Quantitative estimates of the global distributions of cloud-radiative forcing have been obtained from the spaceborne Earth Radiation Budget Experiment (ERBE) launched in 1984. For the April 1985 period, the global shortwave cloud forcing [-44.5 watts per square meter (W/m2)] due to the enhancement of planetary albedo, exceeded in magnitude the longwave cloud forcing (31.3 W/m2) resulting from the greenhouse effect of clouds. Thus, clouds had a net cooling effect on the earth. This cooling effect is large over the mid-and high-latitude oceans, with values reaching -100 W/m2. The monthly averaged longwave cloud forcing reached maximum values of 50 to 100 W/m2 over the convectively disturbed regions of the tropics. However, this heating effect is nearly canceled by a correspondingly large negative shortwave cloud forcing, which indicates the delicately balanced state of the tropics. The size of the observed net cloud forcing is about four times as large as the expected value of radiative forcing from a doubling of CO2. The shortwave and longwave components of cloud forcing are about ten times as large as those for a CO2 doubling. Hence, small changes in the cloud-radiative forcing fields can play a significant role as a climate feedback mechanism. For example, during past glaciations a migration toward the equator of the field of strong, negative cloud-radiative forcing, in response to a similar migration of cooler waters, could have significantly amplified oceanic cooling and continental glaciation.
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... Single-layer, low marine warm clouds cover 25 % of the ocean surface (Charlson et al., 1987) and exert a strong cooling effect on climate due to their reflectivity (Hartmann et al., 1992;Hartmann and Short, 1980;Ramanathan et al., 1989). Aerosols modulate multiple radiative properties of low-level warm clouds, including droplet number concentration (N d ), liquid water path (LWP), geometric, cloud fraction, and lifetime, and their net impact on the cloud radiative forcing is the most uncertain component of the climate system (e.g., Stevens and Feingold, 2009;Christensen et al., 2020;Glass-meier et al., 2021). ...
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... operated under contract no. DE-AC02-05CH11231, using NERSC awards ALCC-ERCAP0025938 and BER-ERCAP0024471. Review statement. This paper was edited by Graham Feingold and reviewed by two anonymous referees. Albrecht, B. A.: Aerosols, Cloud Microphysics, and Fractional Cloudiness, Science, 245, 1227-1230, https://doi.org/10.1126/science.245.4923.1227, 1989 ...
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  • May 2024
  • ATMOS CHEM PHYS
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Article
Full-text available
  • May 2024
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Article
Full-text available
  • Apr 2024
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Preprint
Full-text available
  • Apr 2024
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Article
Full-text available
  • Apr 2024
  • NAT GEOSCI
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Full-text available
  • Apr 2024
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Full-text available
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  • ATMOS CHEM PHYS
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Article
Full-text available
  • Apr 2024
  • GMD
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Article
Full-text available
  • Apr 1987
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Article
Full-text available
  • Apr 1988
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Article
  • Oct 1987
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Article
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Article
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  • J GEOPHYS RES
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A Doubled CO2 Climate Sensitivity Experiment With a Global Model Including a Simple Ocean
Article
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Article
  • Jan 1986
An overview is presented of the uses of top of the atmosphere radiation budget measurements in studies of climate. The net radiative energy flux at the top of the atmosphere must be balanced by local heat storage in the earth-atmosphere column or by horizontal transport in the atmosphere and ocean. Regional variations in the components of the radiation balance are significant and place important constraints on regional and global climate. If suitable time averaging is applied, regional net radiation can be used to infer horizontal transport of energy in the atmosphere and ocean. Estimates of equator-to-pole transport in the atmosphere and ocean based upon currently available top-of-atmosphere radiation budget measurements contain unacceptably large uncertainties associated with uncertainties in the radiation budget measurements themselves. Diurnal and interannual variations in regional radiation balances are large and important but have not yet been properly sampled with broadband instruments. Both have the potential for providing important insights into climate. The role of cloudiness in climate sensitivity remains one of the major uncertainties in quantitative estimates of climate changes associated with particular perturbing influences. Radiation budget data can be used to estimate the effects of actual cloudiness on the top-of-atmosphere heat balance and the dependence of these effects on location and season. The observational studies of the effect of cloudiness on the radiation balance at the top of the atmosphere that have been completed to date all suffer from one or more of three fundamental problems. These are that the parameters of the cloudiness are not accurately known, the radiation budget data are not based on measurements whose frequency response is unbiased in relation to the emissions of the sun and the earth, and the diurnal sampling of the measurements is not complete. The uncertainties associated with each of these problems are expected to be reduced as a result of analyses based on data from the Earth Radiation Budget Experiment. In order that quantitative estimates of climate change be as accurate as possible the general circulation models (GCMs) which produce these forecasts must be critically evaluated with observed data. Many of the most important mechanisms for perturbing climate (e.g., CO2, volcanic aerosols, surface albedo changes) and many of the most important feedback processes (e.g., relative humidity feedback, cloud feedback, ice-albedo feedback) directly involve the radiation balance at the top of the atmosphere and its relation to surface climate. Since the radiation balance at the top of the atmosphere can, in principle, be measured very accurately from space, it is natural that the simulation of top-of-atmosphere energy fluxes by GCMs should be carefully validated against observations. Because of the complexities introduced by clouds, a complete validation of the radiation budget of a GCM is a long and difficult task. A strategy is suggested here in which the clear-sky fluxes of the model are first compared with a clear-sky radiation budget climatology derived from observations. The radiation budgets with clouds included can then also be compared. This procedure should isolate problems not associated with cloudiness and indicate whether, in the grossest sense, the model clouds are correctly influencing the radiation balance. Comparisons between instantaneous synoptic maps of the radiation budget components and numerical forecasts can also be used to diagnose the performance of models.
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The role of Earth Radiation Budget studies in climate and general circulation research
Article
  • Jan 1987
Two decades or near-continuous measurements of earth radiation budget data from satellites have made significant contributions to our understanding of the global mean climate, the greenhouse effect, the meridional radiative heating that drives the general circulation, the influence of radiative heating on regional climate, and climate feedback processes. The remaining outstanding problems largely concern the role of clouds in governing climate, in influencing the general circulation, and in determining the sensitivity of climate to external perturbations, i.e., the so-called cloud feedback problem. In this paper a remarkably simple and effective approach is proposed to address these problems, with the aid of the comprehensive radiation budget data collected by the Earth Radiation Budget Experiment (ERBE). ERBE is a multisatellite experiment which began collecting data in November 1984. The simple approach calls for the estimation of clear-sky fluxes from the high spatial resolution scanner measurements. A cloud-radiative forcing (or simply cloud forcing) is defined which is the difference between clear-sky and cloudy-sky (clear plus overcast skies) fiuxes.The global average of the sum of the solar and long-wave cloud forcing yields directly the net radiative effect (i.e., cooling or warming) of clouds on climate. Furthermore, analyses of variations in clear-sky fluxes and the cloud forcing in terms of temperature variations would yield the radiation-temperature feedbacks, including the mysterious cloud feedback, that are needed to verify present theories of climate. Finally, general circulation model results are used to discuss the nature of the cloud radiative forcing. It is shown that the long-wave effect of clouds is to enhance the meridional heating gradient in the troposphere, while the albedo or solar effect of clouds is largely to reduce the available solar energy at the surface. The long-wave cloud-induced drive for the circulation is particularly large in the monsoon regions. Thus it is concluded that analyses of ERBE data in terms of cloud forcing would add much needed insights into the role of clouds in the general circulation.With respect to the future, the scientific need is discussed for continuing broadband measurements of earth radiation budget data into the next century in order to understand the processes that govern interannual and decadal climate trends. Finally, the spectral variations in clear-sky fluxes and cloud forcing and the need for broadband data to obtain the desired accuracies are described.
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Seasonal Cycle Experiment on the Climate Sensitivity Due to a Doubling of CO2 With an Atmospheric General Circulation Model Coupled to a Simple Mixed-Layer Ocean Model (Paper 4D0745)
Article
  • Oct 1984
A simple slab ocean of 50 m depth, which allows for seasonal ocean heat storage but no ocean heat transport, is coupled to a global spectral general circulation model with global domain, realistic geography, and computed clouds. The paper first describes the atmospheric and oceanic aspects of the model. Following that there is a general discussion of the model control experiment and comparison with observed data. The next two sections describe the zonal mean and geographical responses to a doubling of CO//2 concentration. Following those there is a section with a discussion of the swamp model results compared to the present mixed-layer model results. Finally, the last section draws conclusions from the experiments.
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