Schematic diagram of the CLAW hypothesis (Charlson et al., 1987)[1]
Schematic diagram of the anti-CLAW hypothesis (Lovelock, 2006)[3]
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), first in seawater, and then in the atmosphere. DMS is oxidised in the atmosphere to form sulfur dioxide, and this leads to the production of sulfate aerosols. These aerosols act as cloud condensation nuclei and increase cloud droplet number, which in turn elevate the liquid water content of clouds and cloud 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.[4]
Some subsequent studies of the CLAW hypothesis have uncovered evidence to support its mechanism,[2][5] although this is not unequivocal.[6] 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.[7] A 2014 review article criticised the model for being an oversimplification and that the effect might be much weaker than proposed.[8]
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.[3]
Under future global warming, increasing temperature may stratify the world ocean, decreasing the supply of nutrients from the deep ocean to its productiveeuphotic zone. Consequently, phytoplankton activity will decline with a concomitant 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 consequence of this will be further climate warming which may lead to even less DMS production (and further climate warming). The figure to 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,[9][10] leaving open the possibility that such a mechanism may exist.
^ abCharlson, R. J., Lovelock, J. E., Andreae, M. O. and Warren, S. G. (1987). "Oceanic phytoplankton, atmospheric sulphur, cloud albedo and climate". Nature. 326 (6114): 655–661. Bibcode:1987Natur.326..655C. doi:10.1038/326655a0.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ abAndreae, 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". J. Geophys. Res. 100 (D6): 11335–56. Bibcode:1995JGR...10011335A. doi:10.1029/94JD02828.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^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?". Global Biogeochemical Cycles. 19 (4): GB4002. Bibcode:2005GBioC..19.4002C. doi:10.1029/2004GB002436. hdl:10072/4405.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^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". Global Biogeochemical Cycles. 21 (2): GB2004. Bibcode:2007GBioC..21.2004V. doi:10.1029/2006GB002787. hdl:10261/11184.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^Shaw, G.E.; Benner, R.L.; Cantrell, W.; Clarke, A.D. (1998). "The regulation of climate: A sulfate particle feedback loop involving deep convection — An editorial essay". Climate Change. 39: 23–33. doi:10.1023/A:1005341506115.
^Green, Tamara; Hatton, Angela (1 September 2014). "The CLAW hypothesis: a new perspective on the role of biogenic sulphur in the regulation of global climate". Oceanography and Marine Biology. 52: 315–336.
^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". Nature. 408 (6809): 184–7. Bibcode:2000Natur.408..184C. doi:10.1038/35041539. PMID 11089968.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^Steinacher, M.; Joos, F.; Fr ¨ olicher, T. L.; Bopp, L.; Cadule, P.; Cocco, V.; Doney, S. C.; Gehlen, M.; Lindsay, K.; Moore, J. K.; Schneider, B. & Segschneider, J. (2010). "Projected 21st century decrease in marine productivity: a multi-model analysis". Biogeosciences. 7 (3): 979–1005. doi:10.5194/bg-7-979-2010.
claw, hypothesis, claw, redirects, here, trade, union, zealand, clothing, laundry, allied, workers, union, aotearoa, proposes, negative, feedback, loop, that, operates, between, ocean, ecosystems, earth, climate, hypothesis, specifically, proposes, that, parti. CLAW redirects here For the trade union in New Zealand see Clothing Laundry and Allied Workers Union of Aotearoa The CLAW hypothesis proposes a negative 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 act to stabilise the temperature of the Earth s atmosphere The CLAW hypothesis was originally proposed by Robert Jay Charlson James Lovelock Meinrat Andreae and Stephen G Warren and takes its acronym from the first letter of their surnames 2 Contents 1 CLAW hypothesis 2 Anti CLAW hypothesis 3 See also 4 References 5 External linksCLAW hypothesis Edit Schematic diagram of the CLAW hypothesis Charlson et al 1987 1 Schematic diagram of the anti CLAW hypothesis Lovelock 2006 3 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 first in seawater and then in the atmosphere DMS is oxidised in the atmosphere to form sulfur dioxide and this leads to the production of sulfate aerosols These aerosols act as cloud condensation nuclei and increase cloud droplet number which in turn elevate the liquid water content of clouds and cloud 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 4 Some subsequent studies of the CLAW hypothesis have uncovered evidence to support its mechanism 2 5 although this is not unequivocal 6 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 7 A 2014 review article criticised the model for being an oversimplification and that the effect might be much weaker than proposed 8 Anti CLAW hypothesis EditIn 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 3 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 concomitant 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 consequence of this will be further climate warming which may lead to even less DMS production and further climate warming The figure to 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 9 10 leaving open the possibility that such a mechanism may exist See also EditEarth science Geophysiology Iron fertilizationReferences Edit a b Charlson R J Lovelock J E Andreae M O and Warren S G 1987 Oceanic phytoplankton atmospheric sulphur cloud albedo and climate Nature 326 6114 655 661 Bibcode 1987Natur 326 655C doi 10 1038 326655a0 a href Template Cite journal html title Template Cite journal cite journal a CS1 maint multiple names authors list link 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 J Geophys Res 100 D6 11335 56 Bibcode 1995JGR 10011335A doi 10 1029 94JD02828 a href Template Cite journal html title Template Cite journal cite journal a CS1 maint multiple names authors list link a b Lovelock James 2007 The Revenge of Gaia Penguin ISBN 978 0 14 102597 1 Lovelock J E 2000 1979 Gaia A New Look at Life on Earth 3rd ed Oxford University Press ISBN 0 19 286218 9 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 Global Biogeochemical Cycles 19 4 GB4002 Bibcode 2005GBioC 19 4002C doi 10 1029 2004GB002436 hdl 10072 4405 a href Template Cite journal html title Template Cite journal cite journal a CS1 maint multiple names authors list link 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 Global Biogeochemical Cycles 21 2 GB2004 Bibcode 2007GBioC 21 2004V doi 10 1029 2006GB002787 hdl 10261 11184 a href Template Cite journal html title Template Cite journal cite journal a CS1 maint multiple names authors list link Shaw G E Benner R L Cantrell W Clarke A D 1998 The regulation of climate A sulfate particle feedback loop involving deep convection An editorial essay Climate Change 39 23 33 doi 10 1023 A 1005341506115 Green Tamara Hatton Angela 1 September 2014 The CLAW hypothesis a new perspective on the role of biogenic sulphur in the regulation of global climate Oceanography and Marine Biology 52 315 336 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 Nature 408 6809 184 7 Bibcode 2000Natur 408 184C doi 10 1038 35041539 PMID 11089968 a href Template Cite journal html title Template Cite journal cite journal a CS1 maint multiple names authors list link Steinacher M Joos F Fr olicher T L Bopp L Cadule P Cocco V Doney S C Gehlen M Lindsay K Moore J K Schneider B amp Segschneider J 2010 Projected 21st century decrease in marine productivity a multi model analysis Biogeosciences 7 3 979 1005 doi 10 5194 bg 7 979 2010 External links EditGaia and CLAW Max Planck Institute for Chemistry Mainz DMS and climate Pacific Marine Environmental Laboratory Seattle Retrieved from https en wikipedia org w index php title CLAW hypothesis amp oldid 1118678582, wikipedia, wiki, book, books, library,
