Clathrate gun hypothesis
Encyclopedia
The clathrate gun hypothesis is the popular name given to the hypothesis that rises in sea temperatures (and/or falls in sea level) can trigger the sudden release of methane
from methane clathrate
compounds buried in seabed
s and permafrost
which, because the methane itself is a powerful greenhouse gas
, leads to further temperature rise and further methane clathrate destabilization – in effect initiating a runaway process as irreversible, once started, as the firing of a gun.
In its original form, the hypothesis proposed that the "clathrate gun" could cause abrupt runaway warming in a timescale less than a human lifetime, and might be responsible for warming events in and at the end of the last ice age. This is now thought unlikely.
However, there is stronger evidence that runaway methane clathrate breakdown may have caused drastic alteration of the ocean environment and the atmosphere of earth on a number of occasions in the past, over timescales of tens of thousands of years; most notably in connection with the Permian extinction event
, when 96% of all marine species became extinct 251 million years ago.
, is a form of water ice that contains a large amount of methane within its crystal structure. Potentially large deposits of methane clathrate have been found under sediments on the ocean floors of the Earth, although there are many orders of magnitudes in between the estimates of various experts. In fact, the existence of vast oceanic methane clathrate formation is uncertain and usually only based on reflective seismology and pieces larger than 10 cm have only been recovered from three sites.
The sudden release of large amounts of natural gas from methane clathrate deposits in runaway climate change
could be a cause of past, future, and present climate changes. The release of this trapped methane is a potential major outcome of a rise in temperature; it is thought that this is a main factor in the global warming of 6°C that happened during the end-Permian extinction, as methane is much more powerful as a greenhouse gas than carbon dioxide (despite its atmospheric lifetime of around 12 years, it has a global warming potential
of 72 over 20 years and 25 over 100 years). The theory also predicts this will greatly affect available oxygen content of the atmosphere.
and the Paleocene-Eocene Thermal Maximum
. It may also have had a role in the sudden warm-up of "Snowball Earth
", 630 million years ago. However, warming at the end of the last ice age is not thought to be due to methane release.
) that accumulated in the oceanic water masses prone to stagnation and anoxia (e.g., in silled basins).
. Clathrate deposits destabilize from the deepest part of their stability zone, which is typically hundreds of metres below the seabed. A sustained increase in sea temperature will warm its way through the sediment eventually, and cause the deepest, most marginal clathrate to start to break down; but it will typically take of the order of a thousand years or more for the temperature signal to get through.
One exception, however, may be in clathrates associated with the Arctic ocean
, where clathrates can exist in shallower water stabilized by lower temperatures rather than higher pressures; these may potentially be marginally stable much closer to the surface of the sea-bed, stabilized by a frozen 'lid' of permafrost
preventing methane escape. Recent research carried out in 2008 in the Siberian Arctic has shown millions of tons of methane being released, apparently through perforations in the seabed permafrost, with concentrations in some regions reaching up to 100 times normal. The excess methane has been detected in localized hotspots in the outfall of the Lena River
and the border between the Laptev Sea
and the East Siberian Sea
. Some melting may be the result of geological heating, but more thawing is believed to be due to the greatly increased volumes of meltwater being discharged from the Siberian rivers flowing north. Current methane release has previously been estimated at 0.5 Mt per year. Shakhova et al. (2008) estimate that not less than 1,400 Gt of carbon is presently locked up as methane and methane hydrates under the Arctic submarine permafrost, and 5–10% of that area is subject to puncturing by open talik
s. They conclude that "release of up to 50 Gt of predicted amount of hydrate storage [is] highly
possible for abrupt release at any time". That would increase the methane content of the planet's atmosphere by a factor of twelve, equivalent in greenhouse effect
to a doubling in the current level of CO2.
In 2008 the United States Department of Energy National Laboratory system and the United States Geological Survey's Climate Change Science Program both identified potential clathrate destabilization in the Arctic as one of four most serious scenarios for abrupt climate change, which have been singled out for priority research. The USCCSP released a report in late December 2008 estimating the gravity of this risk.
or global warming
. The explosions and burning of methane would produce lots of smoke and dust, which would lead to global cooling. The methane and carbon dioxide would "create the greenhouse effect, which may lead to global warming". Professor Ryskin writes that it is "difficult to predict" whether global cooling or warming would result.
The evolution of dust and smoke, if it caused global cooling, would likely only last a short time before the particulates washed out of the atmosphere. Then the raised levels of methane and the derivative carbon dioxide would take over. The likely result would be an alternating series of extra cold and extra warm years, arguably more devastating to crop production than a trend in one direction or the other.
It may be possible to explain past marine extinctions by the scrubbing effect. If an inert gas is bubbled through water, the surface of each bubble acts as a semi permeable membrane. Gases diffuse across this membrane according to their concentration inside and outside the bubble. The result of bubbling methane through the ocean is to deplete the oxygen dissolved in the water, leading to ocean anoxia.
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
from methane clathrate
Methane clathrate
Methane clathrate, also called methane hydrate, hydromethane, methane ice, "fire ice", natural gas hydrate or just gas hydrate, is a solid clathrate compound in which a large amount of methane is trapped within a crystal structure of water, forming a solid similar to ice...
compounds buried in seabed
Seabed
The seabed is the bottom of the ocean.- Ocean structure :Most of the oceans have a common structure, created by common physical phenomena, mainly from tectonic movement, and sediment from various sources...
s and permafrost
Permafrost
In geology, permafrost, cryotic soil or permafrost soil is soil at or below the freezing point of water for two or more years. Ice is not always present, as may be in the case of nonporous bedrock, but it frequently occurs and it may be in amounts exceeding the potential hydraulic saturation of...
which, because the methane itself is a powerful greenhouse gas
Greenhouse gas
A greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...
, leads to further temperature rise and further methane clathrate destabilization – in effect initiating a runaway process as irreversible, once started, as the firing of a gun.
In its original form, the hypothesis proposed that the "clathrate gun" could cause abrupt runaway warming in a timescale less than a human lifetime, and might be responsible for warming events in and at the end of the last ice age. This is now thought unlikely.
However, there is stronger evidence that runaway methane clathrate breakdown may have caused drastic alteration of the ocean environment and the atmosphere of earth on a number of occasions in the past, over timescales of tens of thousands of years; most notably in connection with the Permian extinction event
Permian-Triassic extinction event
The Permian–Triassic extinction event, informally known as the Great Dying, was an extinction event that occurred 252.28 Ma ago, forming the boundary between the Permian and Triassic geologic periods, as well as the Paleozoic and Mesozoic eras...
, when 96% of all marine species became extinct 251 million years ago.
Mechanism
Methane clathrate, also known commonly as methane hydrateHydrate
Hydrate is a term used in inorganic chemistry and organic chemistry to indicate that a substance contains water. The chemical state of the water varies widely between hydrates, some of which were so labeled before their chemical structure was understood....
, is a form of water ice that contains a large amount of methane within its crystal structure. Potentially large deposits of methane clathrate have been found under sediments on the ocean floors of the Earth, although there are many orders of magnitudes in between the estimates of various experts. In fact, the existence of vast oceanic methane clathrate formation is uncertain and usually only based on reflective seismology and pieces larger than 10 cm have only been recovered from three sites.
The sudden release of large amounts of natural gas from methane clathrate deposits in runaway climate change
Runaway climate change
Runaway climate change describes a theoretical scenario in which the climate system passes a threshold or tipping point, after which internal positive feedback effects cause the climate to continue changing without further external forcings...
could be a cause of past, future, and present climate changes. The release of this trapped methane is a potential major outcome of a rise in temperature; it is thought that this is a main factor in the global warming of 6°C that happened during the end-Permian extinction, as methane is much more powerful as a greenhouse gas than carbon dioxide (despite its atmospheric lifetime of around 12 years, it has a global warming potential
Global warming potential
Global-warming potential is a relative measure of how much heat a greenhouse gas traps in the atmosphere. It compares the amount of heat trapped by a certain mass of the gas in question to the amount of heat trapped by a similar mass of carbon dioxide. A GWP is calculated over a specific time...
of 72 over 20 years and 25 over 100 years). The theory also predicts this will greatly affect available oxygen content of the atmosphere.
Possible release events
Two events possibly linked in this way are the Permian-Triassic extinction eventPermian-Triassic extinction event
The Permian–Triassic extinction event, informally known as the Great Dying, was an extinction event that occurred 252.28 Ma ago, forming the boundary between the Permian and Triassic geologic periods, as well as the Paleozoic and Mesozoic eras...
and the Paleocene-Eocene Thermal Maximum
Paleocene-Eocene Thermal Maximum
The most extreme change in Earth surface conditions during the Cenozoic Era began at the temporal boundary between the Paleocene and Eocene epochs . This event, the Paleocene–Eocene Thermal Maximum , was associated with rapid global...
. It may also have had a role in the sudden warm-up of "Snowball Earth
Snowball Earth
The Snowball Earth hypothesis posits that the Earth's surface became entirely or nearly entirely frozen at least once, some time earlier than 650 Ma . Proponents of the hypothesis argue that it best explains sedimentary deposits generally regarded as of glacial origin at tropical...
", 630 million years ago. However, warming at the end of the last ice age is not thought to be due to methane release.
Related mechanism: dissolved methane release
Focusing on the Permian-Triassic boundary, Gregory Ryskin http://pangea.stanford.edu/Oceans/GES205/methaneGeology.pdf explores the possibility that mass extinction can be caused by an extremely fast, explosive release of dissolved methane (and other dissolved gases such as carbon dioxide and hydrogen sulfideHydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
) that accumulated in the oceanic water masses prone to stagnation and anoxia (e.g., in silled basins).
Current outlook
Most deposits of methane clathrate are in sediments too deep to respond rapidly, and modelling by Archer (2007) suggests the methane forcing should remain a minor component of the overall greenhouse effectGreenhouse effect
The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface, energy is transferred to the surface and the lower atmosphere...
. Clathrate deposits destabilize from the deepest part of their stability zone, which is typically hundreds of metres below the seabed. A sustained increase in sea temperature will warm its way through the sediment eventually, and cause the deepest, most marginal clathrate to start to break down; but it will typically take of the order of a thousand years or more for the temperature signal to get through.
One exception, however, may be in clathrates associated with the Arctic ocean
Arctic Ocean
The Arctic Ocean, located in the Northern Hemisphere and mostly in the Arctic north polar region, is the smallest and shallowest of the world's five major oceanic divisions...
, where clathrates can exist in shallower water stabilized by lower temperatures rather than higher pressures; these may potentially be marginally stable much closer to the surface of the sea-bed, stabilized by a frozen 'lid' of permafrost
Permafrost
In geology, permafrost, cryotic soil or permafrost soil is soil at or below the freezing point of water for two or more years. Ice is not always present, as may be in the case of nonporous bedrock, but it frequently occurs and it may be in amounts exceeding the potential hydraulic saturation of...
preventing methane escape. Recent research carried out in 2008 in the Siberian Arctic has shown millions of tons of methane being released, apparently through perforations in the seabed permafrost, with concentrations in some regions reaching up to 100 times normal. The excess methane has been detected in localized hotspots in the outfall of the Lena River
Lena River
The Lena is the easternmost of the three great Siberian rivers that flow into the Arctic Ocean . It is the 11th longest river in the world and has the 9th largest watershed...
and the border between the Laptev Sea
Laptev Sea
The Laptev Sea is a marginal sea of the Arctic Ocean. It is located between the northern coast of Siberia, the Taimyr Peninsula, Severnaya Zemlya and the New Siberian Islands. Its northern boundary passes from the Arctic Cape to a point with co-ordinates of 79°N and 139°E, and ends at the Anisiy...
and the East Siberian Sea
East Siberian Sea
The East Siberian Sea is a marginal sea in the Arctic Ocean. It is located between the Arctic Cape to the north, the coast of Siberia to the south, the New Siberian Islands to the west and Cape Billings, close to Chukotka, and Wrangel Island to the east...
. Some melting may be the result of geological heating, but more thawing is believed to be due to the greatly increased volumes of meltwater being discharged from the Siberian rivers flowing north. Current methane release has previously been estimated at 0.5 Mt per year. Shakhova et al. (2008) estimate that not less than 1,400 Gt of carbon is presently locked up as methane and methane hydrates under the Arctic submarine permafrost, and 5–10% of that area is subject to puncturing by open talik
Talik
A talik is a layer of year-round unfrozen ground that lies in permafrost areas. In regions of continuous permafrost, taliks often occur underneath shallow thermokarst lakes and rivers, where the deep water does not freeze in winter, and thus the soil underneath will not freeze either...
s. They conclude that "release of up to 50 Gt of predicted amount of hydrate storage [is] highly
possible for abrupt release at any time". That would increase the methane content of the planet's atmosphere by a factor of twelve, equivalent in greenhouse effect
Greenhouse effect
The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface, energy is transferred to the surface and the lower atmosphere...
to a doubling in the current level of CO2.
In 2008 the United States Department of Energy National Laboratory system and the United States Geological Survey's Climate Change Science Program both identified potential clathrate destabilization in the Arctic as one of four most serious scenarios for abrupt climate change, which have been singled out for priority research. The USCCSP released a report in late December 2008 estimating the gravity of this risk.
Possible outcomes
According to Gregory Ryskin, a sudden release of methane from the ocean may lead to either global coolingGlobal cooling
Global cooling was a conjecture during the 1970s of imminent cooling of the Earth's surface and atmosphere along with a posited commencement of glaciation...
or global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...
. The explosions and burning of methane would produce lots of smoke and dust, which would lead to global cooling. The methane and carbon dioxide would "create the greenhouse effect, which may lead to global warming". Professor Ryskin writes that it is "difficult to predict" whether global cooling or warming would result.
The evolution of dust and smoke, if it caused global cooling, would likely only last a short time before the particulates washed out of the atmosphere. Then the raised levels of methane and the derivative carbon dioxide would take over. The likely result would be an alternating series of extra cold and extra warm years, arguably more devastating to crop production than a trend in one direction or the other.
It may be possible to explain past marine extinctions by the scrubbing effect. If an inert gas is bubbled through water, the surface of each bubble acts as a semi permeable membrane. Gases diffuse across this membrane according to their concentration inside and outside the bubble. The result of bubbling methane through the ocean is to deplete the oxygen dissolved in the water, leading to ocean anoxia.
The consequences of a methane-driven oceanic eruption for marine and
terrestrial life are likely to be catastrophic. Figuratively speaking,
the erupting region "boils over," ejecting a large amount of methane
and other gases (e.g., CO2, H2S) into the atmosphere, and flooding
large areas of land. Whereas pure methane is lighter than air, methane
loaded with water droplets is much heavier, and thus spreads over the
land, mixing with air in the process (and losing water as rain). The
air-methane mixture is explosive at methane concentrations between 5%
and 15%; as such mixtures form in different locations near the ground
and are ignited by lightning, explosions and conflagrations destroy
most of the terrestrial life, and also produce great amounts of smoke
and of carbon dioxide. Firestorms carry smoke and dust into the upper
atmosphere, where they may remain for several years; the resulting
darkness and global cooling may provide an additional kill
mechanism. Conversely, carbon dioxide and the remaining methane create
the greenhouse effect, which may lead to global warming. The outcome
of the competition between the cooling and the warming tendencies is
difficult to predict.http://pangea.stanford.edu/Oceans/GES205/methaneGeology.pdf
In fiction
- The science fiction novel Mother of StormsMother of StormsMother of Storms is a 1994 science fiction novel by John Barnes. It was nominated for three major science fiction awards.-Plot summary:In the early 21st century, the earth suffers from a giant hurricane spawned by the release of clathrate compounds, as the result of a nuclear explosion...
by John BarnesJohn Barnes (author)-Writing:Two of his novels, The Sky So Big and Black and The Duke of Uranium have been reviewed as having content appropriate for a young adult readership, comparing favorably to Robert A. Heinlein's "juvenile" novels...
offers a fictional example of catastrophic climate change caused by methane clathrate release. - In The Life LotteryThe Life LotteryThe Life Lottery, a futuristic eco-thriller, is the final book in Ian Irvine's Human Rites Sequence, set after the events in Terminator Gene, it is also only published in Australia and currently out of print, but will be re-released as a revised edition in March 2010.- Titles of the Human Rites...
by Ian IrvineIan IrvineIan Irvine is an Australian fantasy and eco-thriller author and marine scientist. To date Irvine has written 27 novels, including fantasy, eco-thrillers and books for children. He has had books published in at least 12 countries and continues to write full-time.- Career :Irvine was born in...
unprecedented seismic activity triggers a release of methane hydrate, reversing global cooling. - The hypothesis is the basis of an experiment in the PlayStation 2PlayStation 2The PlayStation 2 is a sixth-generation video game console manufactured by Sony as part of the PlayStation series. Its development was announced in March 1999 and it was first released on March 4, 2000, in Japan...
game Death By DegreesDeath by DegreesDeath by Degrees is an action-adventure video game, developed by Namco. It is initially a spin-off from the Tekken series of fighting games...
. - In TranscendentTranscendent (novel)Transcendent is the third novel in the Destiny's Children series by Stephen Baxter, and a 2006 Campbell Award nominee.-Plot summary:The story alternates between two timelines: the world of Michael Poole in the year 2047, and that of Alia, a posthuman girl who lives approximately half a million...
by Stephen BaxterStephen BaxterStephen Baxter is a prolific British hard science fiction author. He has degrees in mathematics and engineering.- Writing style :...
, averting such a crisis is a major plotline. - The novel The Black Silent by author David DunDavid DunDavid Dun is a thriller writer.David Dun was born and grew up in western Washington but moved to northern California to begin his legal career. He holds a B.A. in psychology from the University of Washington and earned his law degree at Seattle University...
features this idea as a key scientific point. - In the anime Ergo ProxyErgo Proxyis a science fiction suspense anime television series, produced by Manglobe, which premiered across Japan on 25 February 2006 on the WOWOW satellite network. It is directed by Shukō Murase, with screenplay by Dai Satō et al.. Ergo Proxy has been described as dark science fiction mystery with...
, a string of explosions in the methane hydrate reserves wipes out 85% of human life on Earth. - The novel The Far Shore of TimeThe Far Shore of TimeThe Far Shore of Time is a science fiction novel by Frederik Pohl which concludes The Eschaton Sequence and the adventures of Dan Dannerman, an American government agent of the near future who becomes involved with the discovery of advanced and warring aliens.-Plot introduction:Dan Dannerman has...
by Frederik PohlFrederik PohlFrederik George Pohl, Jr. is an American science fiction writer, editor and fan, with a career spanning over seventy years — from his first published work, "Elegy to a Dead Planet: Luna" , to his most recent novel, All the Lives He Led .He won the National Book Award in 1980 for his novel Jem...
features an alien race attempting to destroy humanity by bombing the methane clathrate reserves, thus releasing the gas into the atmosphere. - The novel The SwarmThe Swarm (novel)The Swarm is a science fiction novel by German author Frank Schätzing. It was first published in Germany and Austria in 2004 and soon became a bestseller.-Plot:...
by Frank SchätzingFrank Schätzing' , is a German writer, mostly known for his best-selling science fiction novel The Swarm .- Life :Schätzing was born in Cologne and studied communication studies; he later ran his own company, an advertising agency named INTEVI, in Cologne. Schätzing became a writer in 1990, and penned several...
features what first appear to be freak events related to the world's oceans.
See also
- Abiogenic petroleum originAbiogenic petroleum originAbiogenic petroleum origin is a largely abandoned hypothesis that was proposed as an alternative to theory of biological petroleum origin. It was relatively popular in the past, but it went largely forgotten at the end of the 20th century after it failed to predict the location of new wells.The...
- Abrupt climate changeAbrupt climate changeAn abrupt climate change occurs when the climate system is forced to transition to a new state at a rate that is determined by the climate system itself, and which is more rapid than the rate of change of the external forcing...
- Arctic methane releaseArctic methane releaseArctic methane release is the release of methane from seas and soils in permafrost regions of the Arctic, as part of a more general release of carbon from these soils and seas. Whilst a long-term natural process, it may be exacerbated by global warming. This results in a weak positive feedback...
- Clathrate compoundClathrate compoundA clathrate, clathrate compound or cage compound is a chemical substance consisting of a lattice of one type of molecule trapping and containing a second type of molecule...
- Climate sensitivityClimate sensitivityClimate sensitivity is a measure of how responsive the temperature of the climate system is to a change in the radiative forcing. It is usually expressed as the temperature change associated with a doubling of the concentration of carbon dioxide in Earth's atmosphere.The equilibrium climate...
- Long-term effects of global warmingLong-term effects of global warmingThere are expected to be various long-term effects of global warming. Most discussion and research, including that by the Intergovernmental Panel on Climate Change reports, concentrates on the effects of global warming up to 2100, with only an outline of the effects beyond this...
- Limnic eruptionLimnic eruptionA limnic eruption, also referred to as a lake overturn, is a rare type of natural disaster in which carbon dioxide suddenly erupts from deep lake water, suffocating wildlife, livestock and humans. Such an eruption may also cause tsunamis in the lake as the rising CO2 displaces water. Scientists...
- Mass extinction
- Ocean acidificationOcean acidificationOcean acidification is the name given to the ongoing decrease in the pH and increase in acidity of the Earth's oceans, caused by the uptake of anthropogenic carbon dioxide from the atmosphere....
- Ocean anoxia
- Paleocene-Eocene Thermal MaximumPaleocene-Eocene Thermal MaximumThe most extreme change in Earth surface conditions during the Cenozoic Era began at the temporal boundary between the Paleocene and Eocene epochs . This event, the Paleocene–Eocene Thermal Maximum , was associated with rapid global...
- Permian-Triassic extinction eventPermian-Triassic extinction eventThe Permian–Triassic extinction event, informally known as the Great Dying, was an extinction event that occurred 252.28 Ma ago, forming the boundary between the Permian and Triassic geologic periods, as well as the Paleozoic and Mesozoic eras...
- Physical impacts of climate changePhysical impacts of climate changeThis article is about the physical impacts of climate change. For some of these physical impacts, their effect on social and economic systems are also described.-Definition of climate change:This article refers to reports produced by the IPCC...
- Runaway climate changeRunaway climate changeRunaway climate change describes a theoretical scenario in which the climate system passes a threshold or tipping point, after which internal positive feedback effects cause the climate to continue changing without further external forcings...
- Shutdown of thermohaline circulationShutdown of thermohaline circulationShutdown or slowdown of the thermohaline circulation is a postulated effect of global warming.There is some speculation that global warming could, via a shutdown or slowdown of the thermohaline circulation, trigger localised cooling in the North Atlantic and lead to cooling, or lesser warming, in...
- Storegga SlideStoregga SlideThe three Storegga Slides are considered to be amongst the largest known landslides. They occurred under water, at the edge of Norway's continental shelf , in the Norwegian Sea, 100 km north-west of the Møre coast, causing a very large tsunami in the North Atlantic Ocean...
External links
- Homepage of Dr. Paul Wignal, Reader in Palaeoenvironments, University of Leeds.
- (Abstract) Methane Hydrates in Quaternary Climate Change: The Clathrate Gun Hypothesis
- Ockham's Razor Australian Broadcasting Corporation May 24th, 2009. Melbourne computer specialist Geoff Hudson explains what clathrates are and the danger they pose to climate change.
- Preface to the Clathrate Hydrates special issue
- CCSP, 2008: Abrupt Climate Change. A report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research (Clark, P.U., A.J. Weaver (coordinating lead authors), E. Brook, E.R. Cook, T.L. Delworth, and K. Steffen (chapter lead authors)). U.S. Geological Survey, Reston, VA, 459 pp.
- Arctic permafrost leaking methane at record levels
- Methane Causes Vicious Cycle In Global Warming
- Methane: A Scientific Journey from Obscurity to Climate Super-Stardom Good Sept. 2004 background report from NASA GISS