AA Blog5: YouTube
Geoengineering Marine Stratocumulus to Increase Cloud Albedo:
Where, When and Whether to Inject Aerosols
Hailong Wang, Philip Rasch
Pacific Northwest National Laboratory, Richland, WA
Graham Feingold
NOAA Earth Systems Reasearch Laboratory, Boulder, CO
13th Conference on Cloud Physics, 2 July 2010
Hailong Wang and Philip Rasch from the Pacific Northwest National Laboratory teamed up with Graham Feingold from NOAA Earth Systems Reasearch Laboratory to present to us their research in geoengineering marine stratocumulus to increase cloud albedo.
As we may already know, the Stratocumulus (SC) clouds cover vast regions over oceans and reduce solar heating to these areas. Additional research shows that if cloud albedo is increased by 4%, the warming by atmospheric CO2 can be offset by a factor of 2 according to some arguments.
The presented topic is on the deliberate manipulation of Earth’s climate to counteract the effect of global warming by greenhouse gases (GHGs). These methods of manipulation include solar radiation management through the study of marine cloud albedo enhancement by seawater spray and ocean sulfur cycle enhancement.
Regarding seawater spray method, there has been research done by Latham and Smith (1990) that demonstrated a negative feedback process in which an increase in wind speed, as possible result of atmospheric warming, produces more sea-salt particles to increase cloud albedo and cool the Earth. Latham (1990, 2002) proposed adding submicron sea-salt particles from the ocean surface in a controlled manner to increase marine low-level cloud albedo to offset the forcings.
Wind speed dependence of simulated geoengineering fluxes (red lines) and natural flux of sea spray particles larger than 70 nm (blue lines). Black dotted lines how the Latham (2002) estimate range for a flux needed to produce 400 additional cloud droplets per cubic centimeter.
Salter et al. (2008) demonstrated a wind-driven spray vessel that can produce sea-salt particles to increase CDNC by about 200 cm-3. Process modeling is still needed to understand the transport of injected particles and interactions with clouds.
A number of experiments were designed and executed to produce the following results. In summary, they found that aerosol injection is effective in enhancing cloud albedo in weakly precipitating regimes where an influx of aerosols can prevent the formation of precipitation. This is because the cloud albedo is reduced as cloud formations are reduced after precipitating. Another key area for injection is the post-precipitation regime when CCN are high depleted but the environment is still conducive to cloud formation. The opposite is true for ineffective methods and locations of strongly precipitating regimes and very dry regimes where aerosols cannot form.
