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Title: Marine cloud brightening – as effective without clouds

Abstract

Marine cloud brightening through sea spray injection has been proposed as a climate engineering method for avoiding the most severe consequences of global warming. A limitation of most of the previous modelling studies on marine cloud brightening is that they have either considered individual models or only investigated the effects of a specific increase in the number of cloud droplets. Here we present results from coordinated simulations with three Earth system models (ESMs) participating in the Geoengineering Model Intercomparison Project (GeoMIP) G4sea-salt experiment. Injection rates of accumulation-mode sea spray aerosol particles over ocean between 30°N and 30°S are set in each model to generate a global-mean effective radiative forcing (ERF) of –2.0 W m –2 at the top of the atmosphere. We find that the injection increases the cloud droplet number concentration in lower layers, reduces the cloud-top effective droplet radius, and increases the cloud optical depth over the injection area. We also find, however, that the global-mean clear-sky ERF by the injected particles is as large as the corresponding total ERF in all three ESMs, indicating a large potential of the aerosol direct effect in regions of low cloudiness. The largest enhancement in ERF due to the presence of clouds occur as expected inmore » the subtropical stratocumulus regions off the west coasts of the American and African continents. However, outside these regions, the ERF is in general equally large in cloudy and clear-sky conditions. Lastly, these findings suggest a more important role of the aerosol direct effect in sea spray climate engineering than previously thought.« less

Authors:
 [1];  [2]; ORCiD logo [3]; ORCiD logo [4]; ORCiD logo [5];  [4]
  1. Stockholm Univ., Stockholm (Sweden); Univ. of Oslo, Oslo (Norway)
  2. Met Office Hadley Centre, Exeter (United Kingdom)
  3. Univ. of Oslo, Oslo (Norway); Center for International Climate and Environmental Research - Oslo (CICERO), Oslo (Norway)
  4. Univ. of Oslo, Oslo (Norway)
  5. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1416676
Report Number(s):
PNNL-SA-126314
Journal ID: ISSN 1680-7324; 453040135; TRN: US1800958
Grant/Contract Number:
AC05-76RL01830
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Atmospheric Chemistry and Physics (Online)
Additional Journal Information:
Journal Name: Atmospheric Chemistry and Physics (Online); Journal Volume: 17; Journal Issue: 21; Journal ID: ISSN 1680-7324
Publisher:
European Geosciences Union
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES

Citation Formats

Ahlm, Lars, Jones, Andy, Stjern, Camilla W., Muri, Helene, Kravitz, Ben, and Kristjansson, Jon Egill. Marine cloud brightening – as effective without clouds. United States: N. p., 2017. Web. doi:10.5194/acp-17-13071-2017.
Ahlm, Lars, Jones, Andy, Stjern, Camilla W., Muri, Helene, Kravitz, Ben, & Kristjansson, Jon Egill. Marine cloud brightening – as effective without clouds. United States. doi:10.5194/acp-17-13071-2017.
Ahlm, Lars, Jones, Andy, Stjern, Camilla W., Muri, Helene, Kravitz, Ben, and Kristjansson, Jon Egill. Mon . "Marine cloud brightening – as effective without clouds". United States. doi:10.5194/acp-17-13071-2017. https://www.osti.gov/servlets/purl/1416676.
@article{osti_1416676,
title = {Marine cloud brightening – as effective without clouds},
author = {Ahlm, Lars and Jones, Andy and Stjern, Camilla W. and Muri, Helene and Kravitz, Ben and Kristjansson, Jon Egill},
abstractNote = {Marine cloud brightening through sea spray injection has been proposed as a climate engineering method for avoiding the most severe consequences of global warming. A limitation of most of the previous modelling studies on marine cloud brightening is that they have either considered individual models or only investigated the effects of a specific increase in the number of cloud droplets. Here we present results from coordinated simulations with three Earth system models (ESMs) participating in the Geoengineering Model Intercomparison Project (GeoMIP) G4sea-salt experiment. Injection rates of accumulation-mode sea spray aerosol particles over ocean between 30°N and 30°S are set in each model to generate a global-mean effective radiative forcing (ERF) of –2.0 W m–2 at the top of the atmosphere. We find that the injection increases the cloud droplet number concentration in lower layers, reduces the cloud-top effective droplet radius, and increases the cloud optical depth over the injection area. We also find, however, that the global-mean clear-sky ERF by the injected particles is as large as the corresponding total ERF in all three ESMs, indicating a large potential of the aerosol direct effect in regions of low cloudiness. The largest enhancement in ERF due to the presence of clouds occur as expected in the subtropical stratocumulus regions off the west coasts of the American and African continents. However, outside these regions, the ERF is in general equally large in cloudy and clear-sky conditions. Lastly, these findings suggest a more important role of the aerosol direct effect in sea spray climate engineering than previously thought.},
doi = {10.5194/acp-17-13071-2017},
journal = {Atmospheric Chemistry and Physics (Online)},
number = 21,
volume = 17,
place = {United States},
year = {Mon Nov 06 00:00:00 EST 2017},
month = {Mon Nov 06 00:00:00 EST 2017}
}

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