Methanhydrat und Klimawandel

[Benjamin]

Methanhydrat (Methanklathrat, auch genannt Methaneis bzw. Gaskondensat) besteht aus Methan, das in gefrorenem Wasser eingelagert ist, wobei die Wassermoleküle das Methan vollständig umschließen.
http://de.wikipedia.org/wiki/Methanhydrat

Das Methan liegt in einer hoch verdichteten Form vor, denn ein Liter festes Methanhydrat enthält eine Methanmenge, die unter Normalbedingungen 168 Liter einnimmt.
Bei geschätzten zwölf Billionen Tonnen Methanhydrat ist dort möglicherweise mehr als doppelt so viel Kohlenstoff gebunden als in allen Erdöl-, Erdgas- und Kohlevorräten der Welt.

Methanhydrat kommt gewöhnlich in Tiefen von 500 bis 1000 Metern vor. Methanhydrat bildet sich aus Wasser und Methangas bei einem Druck ab ca. 20 bar; dieser Druck wird ab etwa 190 Meter Wassertiefe erreicht (19 bar Wasserdruck plus 1 bar Luftdruck) und bei Temperaturen von zwei bis vier Grad Celsius.

Im Hinblick auf die Vermutung, dass in den Methanhydratlagerstätten doppelt soviel Kohlenstoff enthalten sein könnte wie in allen bekannten Lagerstätten fossiler Brennstoffe (Erdgas, Erdöl, Kohle, Ölsande) zusammen, fürchten Kritiker, dass die Ausbeutung dieser Lagerstätten - entstanden vor etwa 60 Millionen Jahren im Paläozän - dessen Klima durch den Treibhauseffekt wieder zurückbringen könnte. Am Ende des Paläozän kam es zu einem weltweiten, plötzlichen Temperaturanstieg von ca. 5 bis 6 °C[4]. Das "Late Paleocene Thermal Maximum" wurde durch eine plötzliche Freisetzung von Kohlenstoff bzw. Kohlendioxid ausgelöst. Als Quelle werden instabil gewordene Methanhydratvorkommen am Meeresgrund diskutiert.

Wenn sich warme Meeresströmungen in Richtung Methanfelder verlagern und das Wasser um fünf Grad Celsius erwärmen, kann es zur Freisetzung von großen Mengen Methan kommen (sogenannter Blow-Out-Effekt). Genau dies scheint vor 55 Millionen Jahren geschehen zu sein.

[Benjamin]

25. September 2008

GEFÄHRLICHES METHANHYDRAT
Klimakiller löst sich aus den Tiefen des Eismeeres
Von Christoph Seidler

Gasblasen, die großflächig vom Meeresgrund an die Oberfläche blubbern: Eine russisch-schwedische Arktisexpedition hat ein dramatisches Phänomen im Eismeer beobachtet. Der arktische Meeresboden setzt offenbar große Mengen des Klimakillers Methan frei.

...

URL: http://www.spiegel.de/wissenschaft/n...580213,00.html

[Benjamin]

16. April 2008
AUFTAUENDES METHANEIS
Sibiriens Klimagas-Tresor öffnet sich
Von Volker Mrasek

Ein neuer Klimaschock bahnt sich an: Forscher haben alarmierende Hinweise gefunden, dass der gefrorene Boden im Schelfmeer der Arktis auftaut und eingelagertes Methan freisetzt. Die Folge wäre eine katastrophale Erderwärmung - Methan ist ein noch viel stärkeres Treibhausgas als CO2.

...

URL: http://www.spiegel.de/wissenschaft/n...547716,00.html

[Benjamin]

13. November 2008
ENERGIEQUELLE
Vor Alaska liegt der Methanhydrat-Schatz der USA

Brennbares Gas, in Eis eingeschlossen: Methanhydrat gilt als begehrter Energieträger für die Zeit nach dem Öl. Doch Methan ist gefährlich - es zählt zu den schädlichsten Klimagasen. Nun haben US-Geologen die Methanhydrat-Vorkommen der USA geschätzt.

...

URL: http://www.spiegel.de/wissenschaft/n...590225,00.html

[Benjamin]

Methane clathrates and climate change
http://en.wikipedia.org/wiki/Methane...climate_change

Main article: Clathrate Gun Hypothesis
Methane is a powerful greenhouse gas. Despite its short atmospheric half life of 7 years, methane has a global warming potential of 62 over 20 years and 21 over 100 years (IPCC, 1996; Berner and Berner, 1996; vanLoon and Duffy, 2000). The sudden release of large amounts of natural gas from methane clathrate deposits has been hypothesized as a cause of past and possibly future climate changes. Events possibly linked in this way are the Permian-Triassic extinction event, the Paleocene-Eocene Thermal Maximum.

Climate scientists such as James Hansen expect that methane clathrates in the permafrost regions will be released as a result of global warming, unleashing powerful feedback forces which may cause runaway climate change that cannot be controlled.

Recent research carried out in 2008 in the Siberian Arctic has shown millions of tons of methane being released[23][24][25][26][27] with concentrations in some regions reaching up to 100 times above normal[28][29].

^ Compare: Methane bubbling through seafloor creates undersea hills, Monterey Bay Aquarium Research Institute, 5 February 2007

^ Translation of a blog entry by Örjan Gustafsson, expedition research leader, 2 September 2008

^ N. Shakhova, I. Semiletov, A. Salyuk, D. Kosmach, and N. Bel’cheva (2007), Methane release on the Arctic East Siberian shelf, Geophysical Research Abstracts, 9, 01071

^ N. Shakhova, I. Semiletov, A. Salyuk, D. Kosmach (2008), Anomalies of methane in the atmosphere over the East Siberian shelf: Is there any sign of methane leakage from shallow shelf hydrates?, EGU General Assembly 2008, Geophysical Research Abstracts, 10, EGU2008-A-01526

^ Volker Mrasek, A Storehouse of Greenhouse Gases Is Opening in Siberia, Spiegel International Online, 17 April 2008

5 February 2007 For Immediate Release
Print-friendly PDF version
Methane bubbling through seafloor creates undersea hills
....
According to Paull, "We don't know if this gas and sediment was burped up in a single year, or moved slowly like a glacier." In either case, Paull's data suggest that pingo-like features are growing in response to warming that started thousands of years ago. Thus, their growth is not a result of human-induced global warming. However, Paull's research does show that pingo-like features are still growing and releasing methane today.

Because methane is a potent greenhouse gas, climate scientists would like to know how much is bubbling up from the seafloor worldwide. Future research on methane hydrates and pingo-like features may help address this question. As Paull phrased it, "Pingo-like features are one of the places where we see methane coming up through the seafloor. As yet we don't know how important they are, since we don't know how much gas is coming up in the Arctic as a whole or in other seafloor areas."
....
http://www.mbari.org/news/news_relea...aull-plfs.html

[Benjamin]

Exclusive: The methane time bomb

Arctic scientists discover new global warming threat as melting permafrost releases millions of tons of a gas 20 times more damaging than carbon dioxide

By Steve Connor, Science Editor
Tuesday, 23 September 2008

http://www.independent.co.uk/environ...mb-938932.html


Preliminary findings suggest that massive deposits of subsea methane are bubbling to the surface as the Arctic region becomes warmer and its ice retreats

The first evidence that millions of tons of a greenhouse gas 20 times more potent than carbon dioxide is being released into the atmosphere from beneath the Arctic seabed has been discovered by scientists.

The Independent has been passed details of preliminary findings suggesting that massive deposits of sub-sea methane are bubbling to the surface as the Arctic region becomes warmer and its ice retreats.

Underground stores of methane are important because scientists believe their sudden release has in the past been responsible for rapid increases in global temperatures, dramatic changes to the climate, and even the mass extinction of species. Scientists aboard a research ship that has sailed the entire length of Russia's northern coast have discovered intense concentrations of methane – sometimes at up to 100 times background levels – over several areas covering thousands of square miles of the Siberian continental shelf.

In the past few days, the researchers have seen areas of sea foaming with gas bubbling up through "methane chimneys" rising from the sea floor. They believe that the sub-sea layer of permafrost, which has acted like a "lid" to prevent the gas from escaping, has melted away to allow methane to rise from underground deposits formed before the last ice age.

They have warned that this is likely to be linked with the rapid warming that the region has experienced in recent years.

Methane is about 20 times more powerful as a greenhouse gas than carbon dioxide and many scientists fear that its release could accelerate global warming in a giant positive feedback where more atmospheric methane causes higher temperatures, leading to further permafrost melting and the release of yet more methane.

The amount of methane stored beneath the Arctic is calculated to be greater than the total amount of carbon locked up in global coal reserves so there is intense interest in the stability of these deposits as the region warms at a faster rate than other places on earth.

Orjan Gustafsson of Stockholm University in Sweden, one of the leaders of the expedition, described the scale of the methane emissions in an email exchange sent from the Russian research ship Jacob Smirnitskyi.

"We had a hectic finishing of the sampling programme yesterday and this past night," said Dr Gustafsson. "An extensive area of intense methane release was found. At earlier sites we had found elevated levels of dissolved methane. Yesterday, for the first time, we documented a field where the release was so intense that the methane did not have time to dissolve into the seawater but was rising as methane bubbles to the sea surface. These 'methane chimneys' were documented on echo sounder and with seismic [instruments]."

At some locations, methane concentrations reached 100 times background levels. These anomalies have been seen in the East Siberian Sea and the Laptev Sea, covering several tens of thousands of square kilometres, amounting to millions of tons of methane, said Dr Gustafsson. "This may be of the same magnitude as presently estimated from the global ocean," he said. "Nobody knows how many more such areas exist on the extensive East Siberian continental shelves.

"The conventional thought has been that the permafrost 'lid' on the sub-sea sediments on the Siberian shelf should cap and hold the massive reservoirs of shallow methane deposits in place. The growing evidence for release of methane in this inaccessible region may suggest that the permafrost lid is starting to get perforated and thus leak methane... The permafrost now has small holes. We have found elevated levels of methane above the water surface and even more in the water just below. It is obvious that the source is the seabed."

The preliminary findings of the International Siberian Shelf Study 2008, being prepared for publication by the American Geophysical Union, are being overseen by Igor Semiletov of the Far-Eastern branch of the Russian Academy of Sciences. Since 1994, he has led about 10 expeditions in the Laptev Sea but during the 1990s he did not detect any elevated levels of methane. However, since 2003 he reported a rising number of methane "hotspots", which have now been confirmed using more sensitive instruments on board the Jacob Smirnitskyi.

Dr Semiletov has suggested several possible reasons why methane is now being released from the Arctic, including the rising volume of relatively warmer water being discharged from Siberia's rivers due to the melting of the permafrost on the land.

The Arctic region as a whole has seen a 4C rise in average temperatures over recent decades and a dramatic decline in the area of the Arctic Ocean covered by summer sea ice. Many scientists fear that the loss of sea ice could accelerate the warming trend because open ocean soaks up more heat from the sun than the reflective surface of an ice-covered sea.

[Benjamin]

Methane study reveals serious new climate threat

Renfrey Clarke
10 October 2008
From: Comment & Analysis, Green Left Weekly issue #770 15 October 2008.

Millions of tonnes of the potent greenhouse gas methane have apparently begun leaking from the seabed beneath wide areas of the Arctic Ocean, the British Independent reported on September 23.

Scientists on board the research ship Yakov Smirnitsky recently finished taking precise measurements of methane along Russia’s entire northern coastline. Conducted under the International Siberian Shelf Study 2008, the research revealed methane concentrations as much as 100 times background levels, with the largest anomalies tens of thousands of square kilometers in extent.

“We have found elevated levels of methane above the water surface and even more in the water just below”, researcher Dr Orjan Gustafsson of Stockholm University told the British Independent in an email. “It is obvious that the source is the seabed.”

In some places, the gas was evidently bubbling from the sea floor in volumes too great to be dissolved by the surrounding water. Echo-soundings detected “methane chimneys” reaching all the way to the surface.

Methane, which has the chemical formula CH4, is produced when organic matter decays in an environment poor in oxygen. Vast quantities of methane are locked in the permafrost — frozen earth and swamps — of Arctic landmasses.

Increases in average Arctic temperatures, of some 4°C over recent decades, are now causing the permafrost to melt in summer across wide areas. As a result, growing amounts of Arctic methane are reaching the atmosphere.

Permafrost also extends far onto the shallow seabed of the Arctic continental shelf, where it was flooded as sea levels rose at the end of the last ice age. Until recently, scientists thought the permafrost would form a secure “lid”, keeping the methane in undersea sediments from being released.

As related by the Independent, studies in the 1990s by Dr Igor Semiletov of the Far Eastern Branch of the Russian Academy of Sciences showed no elevated methane levels.
By 2003, the picture had changed. In expeditions to the Laptev Sea off Siberia, Semiletov began finding methane “hot spots” in increasing numbers. Now, the voyage of the Yakov Smirnitsky has yielded evidence that the “lid” is leaking methane across broad regions of the continental shelf.

Semiletov, who is helping prepare the findings of the Siberian Shelf Study for publication, suggests that as permafrost melts on land, rivers are discharging warmer water in growing volumes into the Arctic Ocean. Together with increased warming of ocean waters by the sun as the area of sea ice shrinks, this may be responsible for piercing the undersea permafrost and allowing methane to escape.

The thought of massive additional quantities of methane entering the atmosphere from Arctic sediments is one to ruin the sleep of climate change scientists.

Methane is often described as a greenhouse gas “twenty-five times more powerful” than carbon dioxide (CO2). But this calculation, which averages greenhouse impacts over 100 years, largely misses the point.

Unlike CO2, which once released remains in the atmosphere for centuries, methane is mostly broken down after 10 years and almost completely gone after 20. But so powerful are the greenhouse effects of methane over these 20 years — 72 times the impact of CO2 over the same period — that a large “burst” of methane into the atmosphere could cause rapid warming.

This, in turn, would melt more permafrost and release more methane. And plenty would still remain to be released — as noted by the Independent, the amount of carbon present in Arctic methane is believed to exceed that in the earth’s coal deposits.

Methane in the atmosphere has more than doubled since pre-industrial times. At its present level, of about 2 parts per million, it is the second most powerful greenhouse gas after CO2, accounting for around 20% of the global warming effect. Between 1999 and 2007, atmospheric methane was roughly static, probably as a result of improved industrial and landfill practices and the decline of natural wetlands, an important methane source. But, for the last 18 months or so, the level has again been rising.

The sudden welling up of methane from the Arctic seabed is an ominous sign. Climate scientists will now be watching intently as the researchers involved in the Siberian Shelf Study try to work out how many millions of tonnes of the gas are being released.

Ending the danger from Arctic methane will require lowering temperatures across the region, and restoring sea ice in the Arctic Ocean to something like its earlier extent. For this to happen, big cuts in the atmospheric concentrations of major greenhouse gases will be essential.

[Benjamin]

21.12.2007
Methanhydrat: Aufsteigende Blasen schaden dem Klima nicht

Wissenschaftler vermuten gigantische Mengen an Methanhydrat auf dem Boden der Ozeane. Sein natürlicher Abbau scheint für das Klima einen geringeren Effekt als bisher vermutet darzustellen.

...

http://www.weltderphysik.de/gebiet/p...m-klima-nicht/

[Benjamin]

Beiträge im Deepwave-Blog zu den Themen Methanhydrat und Klimawandel:

http://deepwave.blog.de/?tag=klimawandel
http://deepwave.blog.de/?tag=methanhydrat
##########################################

Erhitzte Meere können Massensterben auslösen
[science.ORF.at, 6.03.07]

In der Erdgeschichte ist es mehrmals zu bisher ungeklärten Massensterben gekommen, in Analogie zu den Dinosauriern haben Geologen einen Meteoriteneinschlag als Grund vermutet. Der US-Geologe Peter D. Ward vertritt eine andere Theorie: Durch die Erhitzung der Atmosphäre kippten die Meere und vergifteten die Atmosphäre. Wenn der aktuellen Klimaerwärmung nicht gegengesteuert wird, könnte der Menschheit ein ähnlich stinkendes Ende bevorstehen.

Zuerst auf Vulkane als Auslöser getippt ...

Im Laufe der Erdgeschichte ereigneten sich immer wieder Massensterben, bei denen ein großer Teil der Lebewesen auf der Erde ausstarb. Prominenteste Opfer der vorerst letzten solchen Katastrophe waren vor 65 Millionen Jahren - am Übergang zwischen Kreidezeit und Tertiär - die Dinosaurier.

Zunächst konnten sich die Paläontologen nur gewaltige Vulkanausbrüche als Auslöser der simultanen Vernichtung vieler biologischer Arten weltweit vorstellen. Tatsächlich herrschte in Zeiten einer Massenextinktion meist auch starke vulkanische Aktivität, von der etwa die riesigen Plateaubasalte in Indien und Sibirien zeugen.

... dann aber auf Meteoriten festgelegt

Doch 1980 entdeckten Forscher um Walter Alvarez große Mengen Iridium in Ablagerungen an der Grenze zwischen den Formationen der Kreidezeit und des Tertiärs. Da dieses Element auf der Erde sehr selten ist, aber häufig in Meteoriten vorkommt, schlossen die Wissenschaftler aus seiner Anreicherung und anderen Indizien, dass damals ein gewaltiger Himmelskörper auf der Erde eingeschlagen sein muss.

An den klimatischen Folgen dieses verheerenden Aufpralls sei ein Großteil des irdischen Lebens zu Grunde gegangen.

Fieberhafte Suche nach Meteoritenspuren

Wenn eine Bombe aus dem All die Dinosaurier ausgelöscht hatte, könnte ähnliches auch schon früher geschehen sein. Forscher in aller Welt suchten deshalb in den vergangenen 25 Jahren nach Indizien für einen Meteoriteneinschlag im Zusammenhang mit den anderen bekannten Massenextinktionen.

Die Ergebnisse waren zwar längst nicht so überzeugend wie an der Grenze zwischen Kreidezeit und Tertiär. Dennoch sah ein Großteil der Paläontologen die Ursache für die Episoden globalen Artensterbens seither im Weltall.

Alternativszenario: Umweltkatastrophe

Der US-Geologe Peter D. Ward erschüttert diese Ansicht nun mit neuen Befunden und präsentiert einen alternativen Extinktionsmechanismus: eine Umweltkatastrophe, bei der in einer Treibhauswelt umkippende Ozeane zu stinkenden Kloaken wurden und Meerwasser wie Atmosphäre mit giftigem Schwefelwasserstoff verpesteten.

Biosphäre über lange Zeit verödet

Zunächst einmal stellt Ward fest, dass im Unterschied zum Untergang der Dinosaurier bei früheren Massensterben die Biosphäre viele Millionen Jahre lang verödet war. Das ergaben neue Untersuchungen über das Mengenverhältnis zweier unterschiedlich schwerer Formen von Kohlenstoff im Gestein.

Kohlenstoff wurde mehr, Pflanzen weniger
Pflanzen bevorzugen bei der Photosynthese Kohlendioxid mit dem leichteren Kohlenstoffatom der Masse 12. Dadurch reichert sich in der Lufthülle die schwerere Form mit der Masse 13 an. Sie wird dann in Kalkgestein eingebaut, das bei Verwitterungsprozessen entsteht.

Steigt in diesem Gestein also der Anteil an leichtem Kohlenstoff sprunghaft an, müssen die Pflanzen dezimiert worden sein. Wirklich findet sich ein solcher Anstieg zeitgleich mit den meisten Massenextinktionen. Zugleich dauert es sehr lange, bis wieder normale Verhältnisse herrschen und die Vegetation sich erholt hat.

Mit neuem Biomarker ...

Diese lange Dauer spricht laut Ward klar gegen einen Meteoriteneinschlag, der nur einen kurzzeitigen Niedergang des Lebens bewirken sollte. Die Ursache des Artensterbens muss vielmehr ein langwieriger Prozess gewesen sein. Auf seine Spur kam der US-Forscher durch einen gleichfalls neu entdeckten Biomarker im Gestein.

Es handelt sich um die Reste von fettähnlichen Stoffen in den Membranen von Mikroorganismen. Sie sind so stabil, dass sie sich bis heute erhalten haben und mit Verfahren wie der Massenspektrometrie nachweisbar sind.

... Schwefelbakterien im Meer entdeckt

Entsprechende Untersuchungen ergaben, dass in Zeiten weltweiten Artensterbens die Weltmeere von Mikroben wimmelten, die Photosynthese treiben und dafür Schwefelwasserstoff benötigen. Es handelt sich um grüne Schwefelbakterien und Schwefelpurpurbakterien. Heute leben sie nur in flachen stehenden Gewässern, die umgekippt und biologisch weitgehend tot sind.

Ihr früheres massenhaftes Vorkommen in den tiefen Ozeanen bedeutet, dass damals dort die gleichen lebensfeindlichen Bedingungen geherrscht haben müssen wie heute in stagnierenden, fauligen Tümpeln. Als Ursache vermutet Ward ein extremes Treibhausklima, ausgelöst durch gewaltige Emissionen an Kohlendioxid und Methan - vermutlich infolge großräumiger vulkanischer Aktivität.

Tiere erstickten in aufgeheizten Meeren ...

Die aufgeheizten Ozeane konnten demnach kaum noch Sauerstoff aufnehmen. Allmählich erstickten dadurch die Meerestiere und sanken auf den Grund, wo sie von anaeroben Bakterien zersetzt wurden, die dabei Schwefelwasserstoff erzeugten. Das giftige Gas stieg empor, reagierte mit dem verbliebenen Sauerstoff und ließ weitere Meeresbewohner verenden. So wurde nach einiger Zeit der gesamte Ozean sauerstofffrei. An seiner Oberfläche breiteten sich die grünen und purpurnen Schwefelbakterien aus.

... und verendeten in verpesteter Luft

Der Schwefelwasserstoff gaste schließlich aus dem Meer aus und verpestete die Luft, so dass er auch vielen Landlebewesen zum Verhängnis wurde. Dabei drang er sogar bis in die Stratosphäre vor, wo er nach den Ergebnissen neuester Untersuchungen die schützende Ozonschicht der Erde angriff.

Somit konnte die schädliche Ultraviolettstrahlung der Sonne bis zum Boden vordringen und auch noch einen Großteil der Lebewesen vernichten, die das Giftgas vertrugen.

Ozeane könnten wieder kippen



Wenn dieses Szenario stimmt, ergeben sich auch bedrohliche Folgerungen für die heutige Zeit. Zum Umkippen der Meere kam es, sobald der Kohlendioxidanteil der Atmosphäre ein Promille überstieg. Nach 0,28 Promille (280 ppm) in vorindustrieller Zeit ist dieser Wert durch anthropogene Emissionen heute bereits auf 0,38 Promille gestiegen.

Sollte sich an der momentanen Emissionsrate nichts ändern, wäre kurz nach dem Ende des nächsten Jahrhunderts die Promillegrenze erreicht und es könnte wieder dazu kommen, dass die Ozeane umkippen. "Wie viel Zeit bliebe dann noch bis zu einem erneuten, durch den Treibhauseffekt verursachten Massensterben", fragt Ward in seinem Artikel und mahnt: "Wir sollten es nicht dazu kommen lassen, das herausfinden zu müssen."

[Benjamin]

Ganz vergessen, hier hatte ich schon etwas zu Methanhydrat gepostet:
http://www.traderboersenboard.de/sho...639#post280639

[Benjamin]

Rising methane levels are cause for concern
Unexplained methane rises raise concerns that our understanding of its role in the global carbon cycle is inadequate, writes Chris Goodall.
10 Nov 2008


Methane concentrations at the Mauna Loa observatory in Hawaii. The grey data points are preliminary. Graphic: NOAA.

We seem to know less about methane emissions than we thought. After a decade of stability, methane concentrations in the atmosphere have been rising strongly in the last 18 months.

Early research work suggested that this rise was concentrated in the northern latitudes of the northern hemisphere and was consistent with greater emissions from decaying organic matter in melting permafrost or from the melting of Arctic sea ice.

Now this result has been called into question by the publication of a new study showing the concentrations of methane are rising almost everywhere. Since methane takes some time to diffuse around the globe, the later work suggests that the rise in methane may not be directly due to enhanced emissions from biological sources.

Methane is the second most important greenhouse gas, producing about 20% of the radiative forcing of all the main gases. Its concentration in the atmosphere has risen about two and half times since the industrial revolution to about 1750 parts per billion.

Although it is present in very much smaller concentrations than CO2, each molecule has a more powerful global warming effect. It also lasts much less long in the atmosphere, typically reacting with the hydroxyl radical (*OH) to form carbon dioxide and water. The average life of a molecule of methane in the atmosphere is about 8 years compared to about a century for carbon dioxide.

The growth rate of methane concentrations in the atmosphere slowed in the second half of the last century. The period between 1999 and early 2007 showed virtually no increase, leading to optimism that methane emissions were under control.

Deep coal mines were an important source and much of the industry was closed down in the northern hemisphere in the 1980s and 1990s. Rice farming practices, which floods vegetated areas, allowing plant matter to rot anaerobically and produce methane, were changed in some parts of Asia to reduce emissions. Natural gas is largely methane and pipeline leaks were also reduced.

The recent rise surprised many researchers. In the past, methane concentrations have tended to increase in periods of marked El Niño (high sea temperatures in the eastern Pacific), resulting in greater dieback of vegetation and more methane production from the rotting plant matter.

But the last year or so has been a period of lower than average temperatures in the Pacific (La Niña rather than El Niño). So this isn't a good explanation for the sudden jump of about 10 parts per billion, or about 0.5% increase in the average concentrations.

Dr Rebecca Fisher of Royal Holloway College, University of London, published work with colleagues early this year showing that the rise in methane was particularly great in the Arctic. Some measuring stations saw increases of twice the average global rise. Since methane takes time to diffuse around the world, this suggested a regionally specific source. It could be from the sea or from rotting vegetation exposed by melting.

Dr Fisher's work was, in a sense, comforting. It suggested we might have an explanation for why methane concentrations were rising. In particular, she showed that increased methane concentrations were associated with rises in the percentage of gas containing the lighter carbon isotope, C12, which is associated with emissions from methane-producing bacteria. It looked as though we could be reasonably confident that at least part of the source of increased emissions was rotting plant matter.

More recent work has dented this belief. MIT scientists have just published work with scientists from Australia and elsewhere that shows that the rise in methane levels has been quite uniform across the globe. This shouldn't happen if methane was produced by plant sources, since there is far more organic matter in the northern hemisphere. Concentrations should be temporarily higher in the north in the months and years it takes methane to spread uniformly across the globe.

The MIT team speculate that the rise in methane may be a function of decreasing concentrations of hydroxyl, the scavenger radical that mops up methane, perhaps as well as increasing emissions. But we don't yet have good monitoring of *OH concentrations and it will be some time before we are able to tell if this hypothesis is correct or, indeed, what is causing this change.

The scientific debate about the cause of increased methane is important because it suggests that we do not yet have a good model for what determines changes in concentrations.

One of the primary worries about global warming is that it will eventually trigger the eruption of untold millions of tonnes of methane from deep sea water. (This is usually known as the 'clathrate gun' hypothesis.) The gas is currently locked into a stable bond with the extremely cold waters in the deep oceans.

Continued world temperature increases will eventually cause the methane to burst from its chemical locks within the cold liquid and rise to the surface. This probably happened at times of rapid warming in the far-distant past.

The fact that we cannot immediately know today why the methane rise is occurring, and whether it is likely to continue, raises worries that our understanding of methane's role in the global carbon cycle is simply not very good.

• This article was shared by our content partner Carbon Commentary, a member of the Guardian Environment Network.

[Benjamin]

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 the seabeds and their permafrost, which because the methane itself is a powerful greenhouse gas, in turn causes further temperature rise and further methane clathrate destabilization – in effect initiating a runaway process, as irreversible once started as the firing of a gun.[1]

http://en.wikipedia.org/wiki/Clathrate_gun_hypothesis

[Benjamin]

18.12.2008
Methan aus dem Meeresboden
Vor Sibiriens Küste entweicht Treibhausgas
von Tinka Wolf

Im eiskalten Sibirien lauert möglicherweise ein tödlicher Klima-Killer. Wissenschaftler haben herausgefunden: Vor der Küste des Landes entweicht Methan aus dem Meeresboden. Das Gas fördert den Treibhauseffekt - und zwar um ein Vielfaches stärker als CO2.

...

Link zum Artikel: http://www.handelsblatt.com/technolo...ausgas;2112193