Cloud reflectivity enhancement

Cloud reflectivity enhancement is also known as 'marine cloud brightening' or 'cloud whitening'. It is a geoengineering technique that works by solar radiation management. By modifying the reflectivity of clouds, the albedo of the Earth is altered. The intention is that this technique, in combination with greenhouse gas emissions reduction (and possibly other geoengineering techniques) will be sufficient to control global warming. This technique is relatively simple and benign, being based as it is on natural processes of 'ocean spray'. It can therefore be deployed quickly for further research, and can then be rolled out on an effective scale relatively cheaply after that. The effect is fully reversible, as the cloud condensation nuclei particles precipitate naturally.

Basic principles

By creating cloud condensation nuclei, geoengineers can change the albedo of clouds to make them appear whiter. This can be done using a variety of chemicals and techniques, with seawater sprays from ships being a simple example. Broadly speaking, the marine environment has a deficit of cloud condensation nuclei due to lower levels of dust and pollution at sea, so this technique is more effective over the ocean than over land.

Proposed schemes

Seawater spray

Various schemes have been suggested, such as that proposed by John Latham and Stephen Salter, which works by spraying seawater in the atmosphere to increase the reflectiveness of clouds. The extra condensation nuclei created by the spray will change the size distribution of the drops in existing clouds to make them whiter. The sprayers would use a fleet of around 1500 unmanned Rotor ships known as Flettner vessels to spray mist created from seawater into the air to thicken clouds and thus reflect more radiation from the Earth. The whitening is achieved as a result of the Twomey effect.

This technique can give >3.7W/m2 of globally-averaged negative forcing, which is sufficient to reverse the warming effect of a doubling of CO2.

Ocean Sulfur Cycle Enhancement

Enhancing the natural sulfur cycle in the Southern Ocean ocean by fertilizing a small portion with iron in order to enhance dimethyl sulfide production and cloud reflectivity. The goal is to slow Antarctic ice from melting and raising sea leve Such techniques also tend to sequester carbon, but in this specific project the enhancement of cloud albedo was both the desired outcome and measured result.

This technique can give only 0.016W/m2 of globally-averaged negative forcing, which is practically insignificant as a contribution to reducing global warming. However, as it is a regionally-acting technique its effects are concentrated in an influence on the climate of Antarctica.

From http://en.wikipedia.org/