Phytoplankton Role
Sulfate aerosol (SO42- and methanesulfonic acid droplets) act as CCNs. These sulfate aerosols form partly from the dimethyl sulfide (DMS) produced by phytoplankton in the open ocean. Large algal blooms in ocean surface waters occur in a wide range of latitudes and contribute considerable DMS into the atmosphere to act as nuclei. The idea that an increase in global temperature would also increase phytoplankton activity and therefore CCN numbers was seen as a possible natural phenomenon that would counteract climate change. An increase of phytoplankton has been observed by scientists in certain areas but the causes are unclear.
A counter-hypothesis is advanced in The Revenge of Gaia, the book by James Lovelock. Warming oceans are likely to become stratified, with most ocean nutrients trapped in the cold bottom layers while most of the light needed for photosynthesis in the warm top layer. Under this scenario, deprived of nutrients, marine phytoplankton would decline, as would sulfate cloud condensation nuclei, and the high albedo associated with low clouds. This is known as the CLAW hypothesis (named after the authors' initials of a 1987 Nature paper) but no conclusive evidence to support this has yet been reported.
Read more about this topic: Cloud Condensation Nuclei
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