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 in themore » 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:

Ahlm, Lars ^[1]; Jones, Andy ^[2]; Stjern, Camilla W.  ^[3];

• Search DOE PAGES for author "Stjern, Camilla W."
• Search DOE PAGES for ORCID "0000-0003-3608-9468"

Muri, Helene  ^[4];

• Search DOE PAGES for author "Muri, Helene"
• Search DOE PAGES for ORCID "0000-0003-4738-493X"

Kravitz, Ben  ^[5];

• Search DOE PAGES for author "Kravitz, Ben"
• Search DOE PAGES for ORCID "0000-0001-6318-1150"

Kristjansson, Jon Egill ^[4]

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+ Show Author Affiliations

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:

Mon Nov 06 00:00:00 EST 2017

Research Org.:

Pacific Northwest National Laboratory (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:

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