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Response to marine cloud brightening in a multi-model ensemble


Stjern, CW and Muri, H and Ahlm, L and Boucher, O and Cole, JNS and Ji, D and Jones, A and Haywood, J and Kravitz, B and Lenton, A and Moore, JC and Niemeier, U and Phipps, SJ and Schmidt, H and Watanabe, S and Kristjansson, JE, Response to marine cloud brightening in a multi-model ensemble, Atmospheric Chemistry and Physics, 18 pp. 621-634. ISSN 1680-7316 (2018) [Refereed Article]


Copyright Statement

Copyright 2018 Author(s). Licensed under Creative Commons Attribution 4.0 International (CC BY 4.0)

DOI: doi:10.5194/acp-18-621-2018


Here we show results from Earth system model simulations from the marine cloud brightening experiment G4cdnc of the Geoengineering Model Intercomparison Project (GeoMIP). The nine contributing models prescribe a 50 % increase in the cloud droplet number concentration (CDNC) of low clouds over the global oceans in an experiment dubbed G4cdnc, with the purpose of counteracting the radiative forcing due to anthropogenic greenhouse gases under the RCP4.5 scenario. The model ensemble median effective radiative forcing (ERF) amounts to −1.9 W m−2, with a substantial inter-model spread of −0.6 to −2.5 W m−2. The large spread is partly related to the considerable differences in clouds and their representation between the models, with an underestimation of low clouds in several of the models. All models predict a statistically significant temperature decrease with a median of (for years 20202069) −0.96 [−0.17 to −1.21] K relative to the RCP4.5 scenario, with particularly strong cooling over low-latitude continents. Globally averaged there is a weak but significant precipitation decrease of −2.35 [−0.57 to −2.96] % due to a colder climate, but at low latitudes there is a 1.19 % increase over land. This increase is part of a circulation change where a strong negative top-of-atmosphere (TOA) shortwave forcing over subtropical oceans, caused by increased albedo associated with the increasing CDNC, is compensated for by rising motion and positive TOA longwave signals over adjacent land regions.

Item Details

Item Type:Refereed Article
Keywords:geoengineering, earth system models, GeoMIP, clouds, climate change, greenhouse gases
Research Division:Earth Sciences
Research Group:Climate change science
Research Field:Climate change processes
Objective Division:Environmental Policy, Climate Change and Natural Hazards
Objective Group:Understanding climate change
Objective Field:Climate change models
UTAS Author:Phipps, SJ (Dr Steven Phipps)
ID Code:123726
Year Published:2018
Web of Science® Times Cited:18
Deposited By:Oceans and Cryosphere
Deposited On:2018-01-22
Last Modified:2018-11-26
Downloads:66 View Download Statistics

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