Open AccessDirect and indirect effects of sea spray geoengineering and the role of injected particle size
Author(s) -
Partanen AnttiIlari,
Kokkola Harri,
Romakkaniemi Sami,
Kerminen VeliMatti,
Lehtinen Kari E. J.,
Bergman Tommi,
Arola Antti,
Korhonen Hannele
Publication year - 2012
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2011jd016428
Subject(s) - aerosol , atmospheric sciences , environmental science , radiative flux , radiative transfer , flux (metallurgy) , sea spray , cloud cover , sea salt , radiative forcing , climatology , climate model , climate change , meteorology , physics , chemistry , oceanography , cloud computing , geology , organic chemistry , quantum mechanics , computer science , operating system
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 CO 2 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.