Title: Low-Cloud Feedbacks from Cloud-Controlling Factors: A Review

Abstract

Here, the response to warming of tropical low-level clouds including both marine stratocumulus and trade cumulus is a major source of uncertainty in projections of future climate. Climate model simulations of the response vary widely, reflecting the difficulty the models have in simulating these clouds. These inadequacies have led to alternative approaches to predict low-cloud feedbacks. Here, we review an observational approach that relies on the assumption that observed relationships between low clouds and the “cloud-controlling factors” of the large-scale environment are invariant across time-scales. With this assumption, and given predictions of how the cloud-controlling factors change with climate warming, one can predict low-cloud feedbacks without using any model simulation of low clouds. We discuss both fundamental and implementation issues with this approach and suggest steps that could reduce uncertainty in the predicted low-cloud feedback. Recent studies using this approach predict that the tropical low-cloud feedback is positive mainly due to the observation that reflection of solar radiation by low clouds decreases as temperature increases, holding all other cloud-controlling factors fixed. The positive feedback from temperature is partially offset by a negative feedback from the tendency for the inversion strength to increase in a warming world, with other cloud-controlling factorsmore » playing a smaller role. A consensus estimate from these studies for the contribution of tropical low clouds to the global mean cloud feedback is 0.25 ± 0.18 W m ^–2 K ^–1 (90% confidence interval), suggesting it is very unlikely that tropical low clouds reduce total global cloud feedback. Because the prediction of positive tropical low-cloud feedback with this approach is consistent with independent evidence from low-cloud feedback studies using high-resolution cloud models, progress is being made in reducing this key climate uncertainty.« less

Authors:

Klein, Stephen A.  ^[1];

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Hall, Alex ^[2]; Norris, Joel R. ^[3]; Pincus, Robert ^[4]

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+ Show Author Affiliations

1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2. Univ. of California, Los Angeles, CA (United States)
3. Univ. of California, San Diego, La Jolla, CA (United States)
4. Univ. of Colorado, Boulder, CO (United States); NOAA Earth System Research Lab., Boulder, CO (United States)

Publication Date:

2017-10-24

Research Org.:

Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1402541

Alternate Identifier(s):

OSTI ID: 1413173

Report Number(s):

LLNL-JRNL-729783
Journal ID: ISSN 0169-3298

Grant/Contract Number:  

AC52-07NA27344

Resource Type:

Published Article

Journal Name:

Surveys in Geophysics

Additional Journal Information:

Journal Volume: 38; Journal Issue: 6; Journal ID: ISSN 0169-3298

Publisher:

Springer

Country of Publication:

United States

Language:

English

Subject:

58 GEOSCIENCES; Climate change; Cloud feedbacks; Low clouds