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The case against climate regulation via oceanic phytoplankton sulphur emissions


More than twenty years ago, a biological regulation of climate was proposed whereby emissions of dimethyl sulphide from oceanic phytoplankton resulted in the formation of aerosol particles that acted as cloud condensation nuclei in the marine boundary layer. In this hypothesis—referred to as CLAW—the increase in cloud condensation nuclei led to an increase in cloud albedo with the resulting changes in temperature and radiation initiating a climate feedback altering dimethyl sulphide emissions from phytoplankton. Over the past two decades, observations in the marine boundary layer, laboratory studies and modelling efforts have been conducted seeking evidence for the CLAW hypothesis. The results indicate that a dimethyl sulphide biological control over cloud condensation nuclei probably does not exist and that sources of these nuclei to the marine boundary layer and the response of clouds to changes in aerosol are much more complex than was recognized twenty years ago. These results indicate that it is time to retire the CLAW hypothesis.

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Figure 1: Modified diagram of the climate feedback loop proposed by ref. 7.
Figure 2: Ocean-derived source of organics to the MBL CCN population.
Figure 3: Major sources and production mechanisms for CCN in the remote MBL.


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We thank our PhD adviser R. J. Charlson for guidance early in our scientific careers. This review should be seen as ‘coming both to praise and bury Caesar’ in that the good that the CLAW hypothesis has done will far outlive its use. We also thank W. E. Asher for comments on this manuscript. This is PMEL contribution number 3697.

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The ideas presented here were developed jointly by P.K.Q. and T.S.B. and both authors participated actively in the writing of the manuscript and the drafting of the figures.

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Correspondence to P. K. Quinn.

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Quinn, P., Bates, T. The case against climate regulation via oceanic phytoplankton sulphur emissions. Nature 480, 51–56 (2011).

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