The
CLAW hypothesis proposes a
feedback loopFeedback describes the situation when output from an event or phenomenon in the past will influence the same event/phenomenon in the present or future....
that operates between
oceanAn ocean is a large body of saline water, and a principal component of the hydrosphere. Approximately 75% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
ecosystemAn ecosystem is a system of interdependent organisms which share the same habitat, in an area functioning together with all of the physical factors of the environment. Ecosystems can be permanent or temporary. Ecosystems usually form a number of food webs...
s and the
EarthEarth is the third planet from the Sun. It is the fifth largest of the eight planets in the solar system, and the largest of the terrestrial planets in the Solar System in terms of diameter, mass and density...
's
climateClimate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and numerous other meteorological elements in a given region over long periods of time...
. The
hypothesisA hypothesis is a proposed explanation for an observable phenomenon. The term derives from the Greek, ὑποτιθέναι - hypotithenai meaning "to put under" or "to suppose." For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...
specifically proposes that particular
phytoplanktonPhytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτον , or "plant", and πλαγκτος , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
that produce
dimethyl sulfideDimethyl sulfide or methylthiomethane is an organosulfur compound with the formula 2S. Dimethyl sulfide is a water-insoluble flammable liquid that boils at and has a characteristic disagreeable odor. It is a component of the smell produced from cooking of certain vegetables, notably...
are responsive to variations in climate forcing, and that these responses lead to a
negative feedback loopNegative feedback occurs when the output of a system acts to oppose changes to the input of the system; with the result that the changes are attenuated. If the overall feedback of the system is negative, then the system will tend to be stable.- Overview :...
that acts to stabilise the
temperatureIn physics, temperature is a physical property of a system that underlies the common notions of hot and cold; something that feels hotter generally has the higher temperature. Temperature is one of the principal parameters of thermodynamics...
of the
Earth's atmosphereThe Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
. The CLAW hypothesis was originally proposed by Robert Charlson,
James LovelockJames Ephraim Lovelock, CH, CBE, FRS is an independent scientist, author, researcher, environmentalist, and futurist who lives in Devon, England...
, Meinrat Andreae and Stephen Warren, and takes its acronym from the first letter of their
surnameA surname is a name added to a given name and is part of a personal name. In many cases a surname is a family name; the family-name meaning first appeared in 1375. Many dictionaries define "surname" as a synonym of "family name". It is also known as a "last name". In some cultures, the surname may...
s.
The hypothesis describes a feedback loop that begins with an increase in the available
energyIn physics, energy is a scalar physical quantity that describes the amount of work that can be performed by a force, an attribute of objects and systems that is subject to a conservation law...
from the
sunThe Sun is the star at the center of the Solar System. The Earth and other matter orbit the Sun, which by itself accounts for about 99.86% of the Solar System's mass....
acting to increase the growth rates of phytoplankton by either a
physiological effectThe Q10 temperature coefficient is a measure of the rate of change of a biological or chemical system as a consequence of increasing the temperature by 10°C. There are many examples where the Q10 is used, one being the calculation of the nerve conduction velocity and another...
(due to elevated
temperatureIn physics, temperature is a physical property of a system that underlies the common notions of hot and cold; something that feels hotter generally has the higher temperature. Temperature is one of the principal parameters of thermodynamics...
) or enhanced
photosynthesisPhotosynthesis is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of Bacteria, but not in Archaea...
(due to increased
irradianceIrradiance, radiant emittance, and radiant exitance are radiometry terms for the power per unit area of electromagnetic radiation at a surface. "Irradiance" is used when the electromagnetic radiation is incident on the surface. "Radiant exitance" or "radiant emittance" is used when the radiation is...
).
The
CLAW hypothesis proposes a
feedback loopFeedback describes the situation when output from an event or phenomenon in the past will influence the same event/phenomenon in the present or future....
that operates between
oceanAn ocean is a large body of saline water, and a principal component of the hydrosphere. Approximately 75% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
ecosystemAn ecosystem is a system of interdependent organisms which share the same habitat, in an area functioning together with all of the physical factors of the environment. Ecosystems can be permanent or temporary. Ecosystems usually form a number of food webs...
s and the
EarthEarth is the third planet from the Sun. It is the fifth largest of the eight planets in the solar system, and the largest of the terrestrial planets in the Solar System in terms of diameter, mass and density...
's
climateClimate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and numerous other meteorological elements in a given region over long periods of time...
. The
hypothesisA hypothesis is a proposed explanation for an observable phenomenon. The term derives from the Greek, ὑποτιθέναι - hypotithenai meaning "to put under" or "to suppose." For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...
specifically proposes that particular
phytoplanktonPhytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτον , or "plant", and πλαγκτος , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
that produce
dimethyl sulfideDimethyl sulfide or methylthiomethane is an organosulfur compound with the formula 2S. Dimethyl sulfide is a water-insoluble flammable liquid that boils at and has a characteristic disagreeable odor. It is a component of the smell produced from cooking of certain vegetables, notably...
are responsive to variations in climate forcing, and that these responses lead to a
negative feedback loopNegative feedback occurs when the output of a system acts to oppose changes to the input of the system; with the result that the changes are attenuated. If the overall feedback of the system is negative, then the system will tend to be stable.- Overview :...
that acts to stabilise the
temperatureIn physics, temperature is a physical property of a system that underlies the common notions of hot and cold; something that feels hotter generally has the higher temperature. Temperature is one of the principal parameters of thermodynamics...
of the
Earth's atmosphereThe Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
. The CLAW hypothesis was originally proposed by Robert Charlson,
James LovelockJames Ephraim Lovelock, CH, CBE, FRS is an independent scientist, author, researcher, environmentalist, and futurist who lives in Devon, England...
, Meinrat Andreae and Stephen Warren, and takes its acronym from the first letter of their
surnameA surname is a name added to a given name and is part of a personal name. In many cases a surname is a family name; the family-name meaning first appeared in 1375. Many dictionaries define "surname" as a synonym of "family name". It is also known as a "last name". In some cultures, the surname may...
s.
The CLAW hypothesis
The hypothesis describes a feedback loop that begins with an increase in the available
energyIn physics, energy is a scalar physical quantity that describes the amount of work that can be performed by a force, an attribute of objects and systems that is subject to a conservation law...
from the
sunThe Sun is the star at the center of the Solar System. The Earth and other matter orbit the Sun, which by itself accounts for about 99.86% of the Solar System's mass....
acting to increase the growth rates of phytoplankton by either a
physiological effectThe Q10 temperature coefficient is a measure of the rate of change of a biological or chemical system as a consequence of increasing the temperature by 10°C. There are many examples where the Q10 is used, one being the calculation of the nerve conduction velocity and another...
(due to elevated
temperatureIn physics, temperature is a physical property of a system that underlies the common notions of hot and cold; something that feels hotter generally has the higher temperature. Temperature is one of the principal parameters of thermodynamics...
) or enhanced
photosynthesisPhotosynthesis is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of Bacteria, but not in Archaea...
(due to increased
irradianceIrradiance, radiant emittance, and radiant exitance are radiometry terms for the power per unit area of electromagnetic radiation at a surface. "Irradiance" is used when the electromagnetic radiation is incident on the surface. "Radiant exitance" or "radiant emittance" is used when the radiation is...
). Certain phytoplankton, such as
coccolithophoridsCoccolithophores are single-celled algae, protists and phytoplankton belonging to the division haptophytes. They are distinguished by special calcium carbonate plates of uncertain function called coccoliths , which are important microfossils...
, synthesise
dimethylsulfoniopropionateDimethylsulfoniopropionate , is a metabolite found in marine phytoplankton, seaweeds and some species of terrestrial and aquatic vascular plants. Older scientific literature refers to it as dimethyl-β-propiothetin...
(DMSP), and their enhanced growth increases the production of this
osmolyteOsmolytes are organic compounds affecting osmosis. They are soluble in the solution within a cell, or in the surrounding fluid, e.g. as plasma osmolytes. They play a role in maintaining cell volume and fluid balance...
. In turn, this leads to an increase in the concentration of its breakdown product,
dimethyl sulfideDimethyl sulfide or methylthiomethane is an organosulfur compound with the formula 2S. Dimethyl sulfide is a water-insoluble flammable liquid that boils at and has a characteristic disagreeable odor. It is a component of the smell produced from cooking of certain vegetables, notably...
(DMS), in first
seawaterSeawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5%. This means that every of seawater has approximately of dissolved salts...
, and then the atmosphere. DMS is oxidised in the atmosphere to form
sulfur dioxideSulfur dioxide is the chemical compound with the formula SO
2. It is produced by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide...
, and this leads to the production of
sulfate aerosolsSulfate aerosols are produced by chemical reactions in the atmosphere from gaseous precursors . The two main sulfate precursors are sulfur dioxide from anthropogenic sources and volcanoes, and dimethyl sulfide from biogenic sources, especially marine plankton...
. These aerosols act as
cloud condensation nucleiCloud condensation nuclei or CCNs are small particles about which cloud droplets coalesce. Water requires a non-gaseous surface to make the transition from a vapour to a liquid. In the atmosphere, this surface presents itself as tiny solid or liquid particles called CCNs...
and increase
cloudA cloud is a visible mass of droplets or frozen crystals suspended in the atmosphere above the surface of the Earth or another planetary body. A cloud is also a visible mass attracted by gravity, such as masses of material in space called interstellar clouds and nebulae...
droplet number, which in turn elevate the liquid water content of clouds and cloud area. This acts to increase
cloud albedoCloud albedo is a measure of the albedo of a cloud - higher values mean that the cloud reflects more solar radiation, or more radiation is transmitted....
, leading to greater
reflectionReflection is the change in direction of a wavefront at an interface between two differentmedia so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves...
of incident
sunlightSunlight, in the broad sense, is the total spectrum of the electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the atmosphere, and the solar radiation is obvious as daylight when the Sun is above the horizon. Near the poles in summer, the days are longer and the...
, and a decrease in the forcing that initiated this chain of events. The figure to the right shows a summarising
schematic diagramright|thumb|300px|A schematic of the [[Washington Metro]]. The schematic is not drawn to scale; distances between stations are fixed and lines are drawn at 45 and 90-degree angles....
. Note that the feedback loop can operate in reverse, 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
dampedIn physics, damping is any effect that tends to reduce the amplitude of oscillations in an oscillatory system, particularly the harmonic oscillator.In mechanics, friction is one such damping effect...
by the loop. As such, the CLAW hypothesis posits an example of
planetary-scaleA planet , is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
homeostasisHomeostasis is the property of a system, either open or closed, that regulates its internal environment and tends to maintain a stable, constant condition...
or
complex adaptive systemComplex adaptive systems are special cases of complex systems. They are complex in that they are diverse and made up of multiple interconnected elements and adaptive in that they have the capacity to change and learn from experience...
, consistent with the
Gaia hypothesisThe Gaia hypothesis is an ecological hypothesis proposing that the biosphere and the physical components of the Earth are closely integrated to form a complex interacting system that maintains the climatic and biogeochemical conditions on Earth in a preferred homeostasis...
framed by one of the original authors of the CLAW hypothesis, James Lovelock.
Some subsequent studies of the CLAW hypothesis have uncovered some evidence to support its mechanism, although this is not unequivocal. Other researchers have suggested that a CLAW-like mechanism may operate in the Earth's
sulfur cycleSulfur is one of the constituents of many proteins, vitamins and hormones. It recycles as in other biogeochemical cycles.The essential steps of the sulfur cycle are:...
without the requirement of an active biological component.
The Anti-CLAW hypothesis
In a recent book,
The Revenge of GaiaThe Revenge of Gaia: Why the Earth is Fighting Back - and How we Can Still Save Humanity is a book by James Lovelock.- Thesis :Lovelock believes that it is too late to avoid significant global heating and significant climate change which will make large parts of the Earth's surface much less...
, Lovelock has proposed that instead of providing negative feedback in the climate system, the components of the CLAW hypothesis may act to create a
positive feedback loopPositive feedback, sometimes referred to as "cumulative causation", refers to a situation where some effect causes more of itself. A system undergoing positive feedback is unstable, that is, it will tend to spiral out of control as the effect amplifies itself....
.
Under future
global warmingGlobal warming is the increase in the average temperature of the Earth's near-surface air and oceans since the mid-20th century and its projected continuation. Global surface temperature increased 0.74 ± 0.18 °C during the last century...
, increasing temperature may
stratifyWater stratification occurs when water of high and low salinity , as well as cold and warm water , forms layers that act as barriers to water mixing....
the
world oceanThe World Ocean, world ocean, or global ocean is the interconnected system of the earth's oceanic waters, and comprises the bulk of the hydrosphere....
, decreasing the supply of
nutrientA nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. Nutrients are the substances that enrich the body. They build and repair tissues, give heat and energy, and regulate body processes...
s from the deep ocean to its
productive400px|thumb|Global oceanic and terrestrial photoautotroph abundance, from September [[1997]] to August 2000. As an estimate of autotroph biomass, it is only a rough indicator of primary production potential, and not an actual estimate of it...
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 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
simulatingA computer simulation, a computer model, or a computational model is a computer program, or network of computers, that attempts to simulate an abstract model of a particular system...
future oceanic primary production have found evidence of declining production with increasing ocean stratification.
See also
- Cloud
A cloud is a visible mass of droplets or frozen crystals suspended in the atmosphere above the surface of the Earth or another planetary body. A cloud is also a visible mass attracted by gravity, such as masses of material in space called interstellar clouds and nebulae...
- Dimethyl sulfide
Dimethyl sulfide or methylthiomethane is an organosulfur compound with the formula 2S. Dimethyl sulfide is a water-insoluble flammable liquid that boils at and has a characteristic disagreeable odor. It is a component of the smell produced from cooking of certain vegetables, notably...
- Earth science
Earth science , is an all-embracing term for the sciences related to the planet Earth. It is arguably a special case in planetary science, the Earth being the only known life-bearing planet...
- Geophysiology
Geophysiology is the study of interaction among living organisms on the Earth operating under the hypothesis that the Earth itself acts as a single living organism ....
- Phytoplankton
Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτον , or "plant", and πλαγκτος , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
External links
- Gaia and CLAW, Max Planck Institute for Chemistry, Mainz
The Max-Planck-Gesellschaft zur Förderung der Wissenschaften Eingetragener Verein is an independent non-profit association of German research institutes funded by the federal and state governments.The nearly 80 research institutes of the Max Planck Society conduct basic research in the interest...