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Geoengineering: Whiter skies?

Kravitz, Ben and MacMartin, Douglas G. and Caldeira, Ken (2012) Geoengineering: Whiter skies? Geophysical Research Letters, 39 (11). Art. No. L11801. ISSN 0094-8276. doi:10.1029/2012GL051652.

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One proposed side effect of geoengineering with stratospheric sulfate aerosols is sky whitening during the day and afterglows near sunset, as is seen after large volcanic eruptions. Sulfate aerosols in the stratosphere would increase diffuse light received at the surface, but with a non-uniform spectral distribution. We use a radiative transfer model to calculate spectral irradiance for idealized size distributions of sulfate aerosols. A 2% reduction in total irradiance, approximately enough to offset anthropogenic warming for a doubling of CO_2 concentrations, brightens the sky (increase in diffuse light) by 3 to 5 times, depending on the aerosol size distribution. The relative increase is less when optically thin cirrus clouds are included in our simulations. Particles with small radii have little influence on the shape of the spectra. Particles of radius ∼0.5 μm preferentially increase diffuse irradiance in red wavelengths, whereas large particles (∼0.9 μm) preferentially increase diffuse irradiance in blue wavelengths. Spectra show little change in dominant wavelength, indicating little change in sky hue, but all particle size distributions produce an increase in white light relative to clear sky conditions. Diffuse sky spectra in our simulations of geoengineering with stratospheric aerosols are similar to those of average conditions in urban areas today.

Item Type:Article
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URLURL TypeDescription
Kravitz, Ben0000-0001-6318-1150
MacMartin, Douglas G.0000-0003-1987-9417
Additional Information:© 2012 American Geophysical Union. Received 9 March 2012; accepted 2 May 2012; published 1 June 2012. We thank Alan Robock for suggesting this topic and for helpful comments throughout the process of drafting this paper, as well as the reviewers for their comments. The Editor thanks the anonymous reviewers for assisting with the evaluation of this paper.
Subject Keywords:aerosols; geoengineering
Issue or Number:11
Record Number:CaltechAUTHORS:20120622-094742783
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Official Citation:Kravitz, B., D. G. MacMartin, and K. Caldeira (2012), Geoengineering: Whiter skies?, Geophys. Res. Lett., 39, L11801, doi:10.1029/2012GL051652.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:32031
Deposited By: Jason Perez
Deposited On:22 Jun 2012 18:34
Last Modified:09 Nov 2021 20:03

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