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CLAW Hypothesis - Wikipedia, the Free Encyclopedia 6/16/12 3:16 PM CLAW Hypothesis from Wikipedia, the Free Encyclopedia CLAW hypothesis - Wikipedia, the free encyclopedia 6/16/12 3:16 PM CLAW hypothesis From Wikipedia, the free encyclopedia The CLAW hypothesis proposes a feedback loop that operates between ocean ecosystems and the Earth's climate.[1] The hypothesis specifically proposes that particular phytoplankton that produce dimethyl sulfide are responsive to variations in climate forcing, and that these responses lead to a negative feedback loop that acts to stabilise the temperature of the Earth's atmosphere. The CLAW hypothesis was originally proposed by Robert Charlson, James Lovelock, Meinrat Andreae and Stephen Warren, and takes its acronym from the first letter of their surnames.[2] Contents 1 The CLAW hypothesis 2 The Anti-CLAW hypothesis 3 See also 4 References 5 External links The CLAW hypothesis The hypothesis describes a feedback loop that begins with an increase in the available energy from the sun acting to increase the growth rates of phytoplankton by either a physiological effect (due to elevated temperature) or enhanced photosynthesis (due to increased irradiance). Certain phytoplankton, such as coccolithophorids, synthesise dimethylsulfoniopropionate (DMSP), and their enhanced growth increases the production of this osmolyte. In turn, this leads to an increase in the concentration of its breakdown product, dimethyl sulfide (DMS), in first seawater, and then the atmosphere. DMS is oxidised in the atmosphere to form sulfur dioxide, and this leads to the production of sulfate aerosols. Schematic diagram of the CLAW These aerosols act as cloud condensation nuclei and increase cloud droplet hypothesis (Charlson et al., number, which in turn elevate the liquid water content of clouds and cloud 1987)[1] area. This acts to increase cloud albedo, leading to greater reflection of incident sunlight, and a decrease in the forcing that initiated this chain of events. The figure to the right shows a summarising schematic diagram. Note that the feedback loop can operate in the reverse direction, such that a decline in solar energy leads to reduced cloud cover and thus to an increase in the amount of solar energy reaching the Earth's surface. A significant feature of the chain of interactions described above is that it creates a negative feedback loop, whereby a change to the climate system (increased/decreased solar input) is ultimately counteracted and damped by the loop. As such, the CLAW hypothesis posits an example of planetary-scale homeostasis or complex adaptive system, consistent with the Gaia hypothesis framed by one of the original authors of the CLAW hypothesis, James Lovelock.[3] Some subsequent studies of the CLAW hypothesis have uncovered evidence to support its mechanism,[2][4] http://en.wikipedia.org/wiki/CLAW_hypothesis Page 1 of 3 CLAW hypothesis - Wikipedia, the free encyclopedia 6/16/12 3:16 PM although this is not unequivocal.[5] Other researchers have suggested that a CLAW-like mechanism may operate in the Earth's sulfur cycle without the requirement of an active biological component.[6] The Anti-CLAW hypothesis In his 2006 book, The Revenge of Gaia, Lovelock proposed that instead of providing negative feedback in the climate system, the components of the CLAW hypothesis may act to create a positive feedback loop.[7] Under future global warming, increasing temperature may stratify the world ocean, decreasing the supply of nutrients from the deep ocean to its productive euphotic zone. Consequently, phytoplankton activity will decline with a concommitant fall in the production of DMS. In a reverse of the CLAW hypothesis, this decline in DMS production will lead to a decrease in cloud condensation nuclei and a fall in cloud albedo. The Schematic diagram of the anti- consequence of this will be further climate warming which may lead to CLAW hypothesis (Lovelock, even less DMS production (and further climate warming ...). The figure to 2006)[7] the right shows a summarising schematic diagram. Evidence for the anti-CLAW hypothesis is constrained by similar uncertainties as those of the sulfur cycle feedback loop of the CLAW hypothesis. However, researchers simulating future oceanic primary production have found evidence of declining production with increasing ocean stratification.[8] See also Cloud Coccolithophorid Dimethyl sulfide Dimethylsulfoniopropionate Earth science Geophysiology Phytoplankton References 1. ^ a b Charlson, R. J., Lovelock, J. E., Andreae, M. O. and Warren, S. G. (1987). "Oceanic phytoplankton, atmospheric sulphur, cloud albedo and climate" (http://www.nature.com/nature/journal/v326/n6114/abs/326655a0.html) . Nature 326 (6114): 655–661. Bibcode 1987Natur.326..655C (http://adsabs.harvard.edu/abs/1987Natur.326..655C) . DOI:10.1038/326655a0 (http://dx.doi.org/10.1038%2F326655a0) . http://www.nature.com/nature/journal/v326/n6114/abs/326655a0.html. 2. ^ a b Andreae, M. O., Elbert, W. and Demora, S. J. (1995). "Biogenic sulfur emissions and aerosols over the tropical South Atlantic, 3. Atmospheric dimethylsulfide, aerosols and cloud condensation nuclei" (http://www.agu.org/pubs/crossref/1995/94JD02828.shtml) . J. Geophys. Res. 100: 11335–56. Bibcode 1995JGR...10011335A (http://adsabs.harvard.edu/abs/1995JGR...10011335A) . DOI:10.1029/94JD02828 (http://dx.doi.org/10.1029%2F94JD02828) . http://www.agu.org/pubs/crossref/1995/94JD02828.shtml. 3. ^ Lovelock, J.E. (2000) [1979]. Gaia: A New Look at Life on Earth (3rd ed.). Oxford University Press. ISBN 0-19- 286218-9. 4. ^ Cropp, R.A., Gabric, A.J., McTainsh, G.H., Braddock, R.D. and Tindale, N. (2005). "Coupling between ocean biota and atmospheric aerosols: Dust, dimethylsulphide, or artifact?" http://en.wikipedia.org/wiki/CLAW_hypothesis Page 2 of 3 CLAW hypothesis - Wikipedia, the free encyclopedia 6/16/12 3:16 PM (http://www.agu.org/pubs/crossref/2005/2004GB002436.shtml) . Global Biogeochemical Cycles 19 (4): GB4002. Bibcode 2005GBioC..19.4002C (http://adsabs.harvard.edu/abs/2005GBioC..19.4002C) . DOI:10.1029/2004GB002436 (http://dx.doi.org/10.1029%2F2004GB002436) . http://www.agu.org/pubs/crossref/2005/2004GB002436.shtml. 5. ^ Vallina, S. M., Simo, R., Gasso, S., De Boyer-Montegut, C., del Rio, E., Jurado, E. and Dachs, J. (2007). "Analysis of a potential "solar radiation dose-dimethylsulfide-cloud condensation nuclei" link from globally mapped seasonal correlations" (http://www.agu.org/pubs/crossref/2007/2006GB002787.shtml) . Global Biogeochemical Cycles 21 (2): GB2004. Bibcode 2007GBioC..21.2004V (http://adsabs.harvard.edu/abs/2007GBioC..21.2004V) . DOI:10.1029/2006GB002787 (http://dx.doi.org/10.1029%2F2006GB002787) . http://www.agu.org/pubs/crossref/2007/2006GB002787.shtml. 6. ^ Shaw, G.E., Benner, R.L., Cantrell, W. and Clarke, A.D. (1998). "The regulation of climate: A sulfate particle feedback loop involving deep convection — An editorial essay" (http://www.ingentaconnect.com/content/klu/clim/1998/00000039/00000001/00164320) . Climate Change 39: 23–33. DOI:10.1023/A:1005341506115 (http://dx.doi.org/10.1023%2FA%3A1005341506115) . http://www.ingentaconnect.com/content/klu/clim/1998/00000039/00000001/00164320. 7. ^ a b Lovelock, James (2007). The Revenge of Gaia. Penguin. ISBN 0-14-102597-2. 8. ^ Cox, P. M., Betts, R. A., Jones, C. D., Spall, S. A. and Totterdell, I. J. (2000). "Acceleration of global warming due to carbon-cycle feedbacks in a coupled climate model" (http://www.nature.com/nature/journal/v408/n6809/abs/408184a0.html) . Nature 408 (6809): 184–7. DOI:10.1038/35041539 (http://dx.doi.org/10.1038%2F35041539) . PMID 11089968 (//www.ncbi.nlm.nih.gov/pubmed/11089968) . http://www.nature.com/nature/journal/v408/n6809/abs/408184a0.html. External links Gaia and CLAW (http://www.atmosphere.mpg.de/enid/1w1.html) , Max Planck Institute for Chemistry, Mainz DMS and climate (http://saga.pmel.noaa.gov/review/dms_climate.html) , Pacific Marine Environmental Laboratory, Seattle Retrieved from "http://en.wikipedia.org/w/index.php?title=CLAW_hypothesis&oldid=495799085" Categories: Atmospheric radiation Climate feedbacks Particulates Satellite meteorology and remote sensing This page was last modified on 3 June 2012 at 17:16. Text is available under the Creative Commons Attribution-ShareAlike License; additional terms may apply. See Terms of use for details. Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. http://en.wikipedia.org/wiki/CLAW_hypothesis Page 3 of 3.
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