Cloud optical thickness feedbacks in the CO2 climate problem

Somerville, Richard C. J.

doi:10.1016/0273-1177(85)90323-0

Cited by 72 publications

(101 citation statements)

References 24 publications

(18 reference statements)

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“…Large changes in cloud radiative effect on the surface energy budget occur in coupled climate models due to cloud phase and microphysics changes (34), temperature effects on adiabatic water content (35)(36)(37), and changes in large-scale moisture convergence and evaporation (29). Furthermore, observations of internal variability and trends indicate that a warmer Arctic will also likely be cloudier in winter (38,39).…”

Section: Discussionmentioning

confidence: 99%

Low clouds suppress Arctic air formation and amplify high-latitude continental winter warming

Cronin

Tziperman

2015

Proc. Natl. Acad. Sci. U.S.A.

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High-latitude continents have warmed much more rapidly in recent decades than the rest of the globe, especially in winter, and the maintenance of warm, frost-free conditions in continental interiors in winter has been a long-standing problem of past equable climates. We use an idealized single-column atmospheric model across a range of conditions to study the polar night process of air mass transformation from high-latitude maritime air, with a prescribed initial temperature profile, to much colder high-latitude continental air. We find that a low-cloud feedback-consisting of a robust increase in the duration of optically thick liquid clouds with warming of the initial state-slows radiative cooling of the surface and amplifies continental warming. This low-cloud feedback increases the continental surface air temperature by roughly two degrees for each degree increase of the initial maritime surface air temperature, effectively suppressing Arctic air formation. The time it takes for the surface air temperature to drop below freezing increases nonlinearly to ∼10 d for initial maritime surface air temperatures of 20°C. These results, supplemented by an analysis of Coupled Model Intercomparison Project phase 5 climate model runs that shows large increases in cloud water path and surface cloud longwave forcing in warmer climates, suggest that the "lapse rate feedback" in simulations of anthropogenic climate change may be related to the influence of low clouds on the stratification of the lower troposphere. The results also indicate that optically thick stratus cloud decks could help to maintain frost-free winter continental interiors in equable climates.global warming | polar amplification | cloud feedbacks | paleoclimate O ne of the persistent mysteries of the "equable climates" of the Eocene and Cretaceous, ∼ 143-33 million years ago, is the warmth of midlatitude and high-latitude continental interiors during winter and, in particular, the frost-intolerant flora and fauna in parts of what is now Wyoming and southern Canada (1). Climate models can simulate warm conditions over the ocean, but they have difficulty simulating continental warmth away from the moderating effects of the ocean, especially if tropical warming is constrained to be K10°C. Although recent work suggests a relaxation of such tropical constraints (2), model−data agreement has been found only for model CO 2 concentrations that seem unrealistically high, and the mechanisms that maintain high-latitude warmth over land remain poorly understood (2, 3). Previous proposed mechanisms to explain the overall reduction of the equator−pole temperature contrast in equable climates include polar stratospheric clouds (4, 5), dramatic expansion of the Hadley circulation (6), increased poleward ocean heat transport due to ocean mixing by stronger tropical cyclones (7,8), and a convective cloud feedback (9). The convective cloud feedback has now appeared in multiple simulations of past and future climates at high CO 2 (10, 11) but is not effective at explaining wa...

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Section: Discussionmentioning

confidence: 99%

Low clouds suppress Arctic air formation and amplify high-latitude continental winter warming

Cronin

Tziperman

2015

Proc. Natl. Acad. Sci. U.S.A.

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“…Even if the planetary radiation balance simulated with microphysics is no more accurate than that simulated without microphysics, the treatment of cloud microphysics in the GCM is still preferred, because the additional feedback mechanisms represented with microphysics make the microphysics version more versatile for climate sensitivity studies. The sensitivity of cloud water to temperature [Somerville and Remer, 1984] can be treated in a physically based manner. By distinguishing cloud water and cloud ice, cloud radiative properties are more realistic than those in the NCAR version, so that the sensitivity of cloud particle phase (and hence cloud reflectivity and settling velocity) to temperature can be treated [Smith, 1990].…”

Section: Discussionmentioning

confidence: 99%

Application of cloud microphysics to NCAR community climate model

Ghan¹,

Leung²,

Hu³

1997

J. Geophys. Res.

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Abstract. The Colorado State University Regional Atmospheric Modeling System bulk cloud microphysics parameterization has been applied to the treatment of stratiform clouds in the National Center for Atmospheric Research community climate model. Predicted cloud properties are mass concentrations of cloud water, cloud ice, rain, and snow and number concentration of ice. Microphysical processes treated include condensation of water vapor and evaporation of cloud water and rain, nucleation of ice crystals, vapor deposition and sublimation of cloud ice and snow, autoconversion and accretion of cloud water, aggregation and collection of cloud ice, melting of ice and snow, timing on ice and snow, and gravitational settling of ice, rain, and snow. Although the parameterization is more detailed and hence more computationally demanding than other cloud microphysics parameterizations in climate models, it treats the Bergeron-Findeisen process explicitly and hence does not require an ad hoc parameterization to distinguish liquid water and ice. A variety of simulations were performed, testing sensitivity to horizontal and vertical resolution, the treatment of ice number, droplet number, and parameterization of cumulus convection. The simulated planetary radiation balance is found to be particularly sensitive to the treatment of ice number and cumulus convection.

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“…The cloud-scale average condensate mixing ratio within individual cloud elements has been shown, in both observational and theoretical studies (e.g., Feigelson, 1978;Somerville and Remer, 1984;Betts and Harshvardhan, 1987;Platt and Harshvardhan, 1988), to vary systematically with temperature; these cloud-scale average mixing ratios are controlled by microphysical and small-scale cloud-dynamical processes, and so should be amenable to semi-empirical parameterization.…”

Section: Fractional Cloudinessmentioning

confidence: 99%

“…In addition, the variability of cloud optical properties with temperature and other atmospheric state variables is now being recognized as a potentially important aspect of cloudclimate feedback (e.g., Somerville and Remer, 1984;Platt and Harshvardhan, 1988). New, physically based fractional cloudiness schemes (e.g., Randall, 1987) are linking cloud amount with turbulence variables.…”

Section: Introductionmentioning

confidence: 99%

Cloud parameterization for climate modeling: Status and prospects

Randall

1989

Atmospheric Research

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Cloud optical thickness feedbacks in the CO2 climate problem

Cited by 72 publications

References 24 publications

Low clouds suppress Arctic air formation and amplify high-latitude continental winter warming

Low clouds suppress Arctic air formation and amplify high-latitude continental winter warming

Application of cloud microphysics to NCAR community climate model

Cloud parameterization for climate modeling: Status and prospects

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