Paper: sea spray geoengineering (Partanen et al., 2012)

[Sam Carana]

Direct and indirect effects of sea spray geoengineering and the role
of injected particle size
Partanen et al., 2012
http://www.agu.org/pubs/crossref/2012/2011JD016428.shtml

Climate-aerosol model ECHAM5.5-HAM2 was used to investigate how
geoengineering with artificial sea salt emissions would affect marine
clouds and the Earth's radiative balance. Prognostic cloud droplet
number concentration and interaction of aerosol particles with clouds
and radiation were calculated explicitly, thus making this the first
time that aerosol direct effects of sea spray geoengineering are
considered.

When a wind speed dependent baseline geoengineering flux was applied
over all oceans (total annual emissions 443.9 Tg), we predicted a
radiative flux perturbation (RFP) of -5.1 W m-2, which is enough to
counteract warming from doubled CO2 concentration.

When the baseline flux was limited to three persistent stratocumulus
regions (3.3% of Earth's surface, total annual emissions 20.6 Tg), the
RFP was -0.8 Wm-2 resulting mainly from a 74-80% increase in cloud
droplet number concentration and a 2.5-4.4 percentage point increase
in cloud cover.

Multiplying the baseline mass flux by 5 or reducing the injected
particle size from 250 to 100 nm had comparable effects on the
geoengineering efficiency with RFPs -2.2 and -2.1 Wm-2, respectively.

Within regions characterized with persistent stratocumulus decks,
practically all of the radiative effect originated from aerosol
indirect effects. However, when all oceanic regions were seeded, the
direct effect with the baseline flux was globally about 29% of the
total radiative effect.

Together with previous studies, our results indicate that there are
still large uncertainties associated with the sea spray geoengineering
efficiency due to variations in e.g., background aerosol
concentration, updraft velocity, cloud altitude and onset of
precipitation.

[Sam Carana]

Peter Blossey, Cloud Modeling scientist at University of Washington,
has compiled a good list with related papers, at:
http://www.atmos.washington.edu/~bloss/cloud_climate_list.html