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Title: Response to marine cloud brightening in a multi-model ensemble

In this paper 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 Wm –2, with a substantial inter-model spread of –0.6 to –2.5 Wm –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 2020–2069) –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-atmospheremore » (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.« less
ORCiD logo [1] ; ORCiD logo [2] ;  [3] ; ORCiD logo [4] ;  [5] ;  [6] ;  [7] ;  [7] ; ORCiD logo [8] ;  [9] ;  [10] ;  [11] ; ORCiD logo [12] ;  [11] ;  [13] ;  [2]
  1. CICERO Center for International Climate and Environmental Research Oslo, Oslo (Norway); Univ. of Oslo, Oslo (Norway)
  2. Univ. of Oslo, Oslo (Norway)
  3. Univ. of Oslo, Oslo (Norway); Stockholm Univ., Stockholm (Sweden)
  4. Stockholm Univ., Stockholm (Sweden)
  5. Canadian Centre for Climate Modelling and Analysis, Victoria (Canada)
  6. Beijing Normal University, Beijing (China)
  7. Met Office Hadley Centre, Exeter (United Kingdom)
  8. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  9. CSIRO Oceans and Atmosphere, Hobart (Australia)
  10. Beijing Normal University, Beijing (China); Joint Center for Global Change Studies, Beijing (China); Univ. of Lapland, Rovaniemi (Finland)
  11. Max Planck Institute for Meteorology, Hamburg (Germany)
  12. Univ. of Tasmania, Hobart (Australia)
  13. Japan Agency for Marine-Earth Science and Technology, Yokohama (Japan)
Publication Date:
Report Number(s):
Journal ID: ISSN 1680-7324
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Atmospheric Chemistry and Physics (Online)
Additional Journal Information:
Journal Name: Atmospheric Chemistry and Physics (Online); Journal Volume: 18; Journal Issue: 2; Journal ID: ISSN 1680-7324
European Geosciences Union
Research Org:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org:
Country of Publication:
United States
OSTI Identifier: