Twomey effect

Twomey effect

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Twomey effect — describes how cloud condensation nuclei
Cloud condensation nuclei
Cloud condensation nuclei or CCNs are small particles typically 0.2 µm, or 1/100 th the size of a cloud droplet ) about which cloud droplets coalesce. Water requires a non-gaseous surface to make the transition from a vapour to a liquid. In the atmosphere, this surface presents itself as tiny...

 (CCN), possibly from anthropogenic pollution, may increase the amount of solar radiation reflected by clouds. This is an indirect effect.

Aerosol particles can act as CCN's creating more droplets which have a smaller size distribution. This increases the cloud albedo
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

as clouds appear whiter and larger, leading to a cooling of between -0.3 and -1.8 Wm−2. For example we observe trails of white clouds from ships crossing the oceans due to this effect.