THE RELATIONSHIPS BETWEEN MARINE PHYTOPLANKTON, DIMETHYLSULPHIDE AND THE GLOBAL CLIMATE: THE CLAW HYPOTHESIS AS A LAKATOSIAN PROGRESSIVE PROBLEMSHIFT
Authors: Nei Freitas Nunes-Neto, Ricardo Santos do Carmo and Charbel Niño El-Hani
Abstract: In this chapter, we address the origin and development of a scientific hypothesis about the connection between some species of marine phytoplankton, sulphur compounds, and clouds over the oceans. This hypothesis is very relevant to the understanding of the climate system. Investigations carried out by Lovelock and colleagues in the beginnings of the 1970s were important to the construction of this hypothesis. Those studies searched for a stable intermediary in the sulphur cycle, which would be responsible for transferring this element from the oceans to the land surface. Based on studies about the release of dimethylsulphide (DMS, a volatile sulphur compound) by marine phytoplankton species, as well as the process of cloud formation and its relationship with planetary albedo, Charlson, Lovelock, Andreae and Warren proposed in 1987 what became known as the CLAW hypothesis. This hypothesis proposes that the rapid oxidation of DMS in the atmosphere leads to the formation of a non-sea-salt aerosol (NSS–SO4 2-), which, when oxidized, constitutes nuclei required for the condensation of water vapor, and, thus, to cloud formation over the oceans.