|
|
|
|
Arctic methane release
|
| |
|
| |
Methane is a powerful greenhouse gas. It has many natural sources, of which the Arctic is a currently minor one, although global warming may accelerate its release from the Arctic region dramatically. Although the Arctic release rate has increased recently, atmospheric methane levels have been stable over the past decade, as the lack of increase from other sources dominates.
Large quantities of methane are stored in the Arctic in natural gas deposits, permafrost, and as submarine clathrates.
Discussion
Ask a question about 'Arctic methane release' Start a new discussion about 'Arctic methane release' Answer questions from other users |
Encyclopedia
Methane is a powerful greenhouse gas. It has many natural sources, of which the Arctic is a currently minor one, although global warming may accelerate its release from the Arctic region dramatically. Although the Arctic release rate has increased recently, atmospheric methane levels have been stable over the past decade, as the lack of increase from other sources dominates.
Large quantities of methane are stored in the Arctic in natural gas deposits, permafrost, and as submarine clathrates. Methane is also transported to the region in rivers. Permafrost and clathrates degrade on warming, thus large releases of methane from these sources are expected as a result of global warming. Any methane released from the Arctic as a result of global warming will tend to cause additional global warming. This is known as positive feedback. If the gain in this feedback loop is sufficient, this may cause a runaway warming event. Buffett and Archer suggest that such an event is currently possible, although it will take place over millennia.
During interglacials, average atmospheric methane concentrations are nearly twice the lowest values in the depths of glacial. During interglacials, there is an interhemispheric asymmetry in methane concentration; concentrations in the Arctic atmosphere are higher by 8–10% than that in the Antarctica atmosphere. During cold glacier epochs, this gradient decreases to practically insignificant levels. Land ecosystems are considered the main sources of this asymmetry, although it has been suggested that 'the role of the Arctic Ocean is significantly underestimated'.
Methane released from seas and oceans in this region come from sources including submarine taliks, river transport, ice complex retreat, submarine permafrost and decaying gas hydrate deposits (clathrate). Natural gas leakage has also been suggested as a methane source.
Risk of abrupt climate change
The release of methane from the Arctic is in itself a contributor to global warming. It is induced by Arctic shrinkage and the recent thawing of seabed permafrost. Recent observations of accelerated release in arctic ocean regions of may indicate a worsening positive feedback loop, with the increased atmospheric methane causing additional warming, which turn will cause further methane releases. Land-based permafrost, also in the Siberian Arctic, was also recently observed to be releasing large amounts of methane, estimated at over 4 million tons - significantly above previous estimates.
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 taliks. 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..
In 2008 the United States Department of Energy National Laboratory system identified potential clathrate destabilization in the Arctic as one the most serious scenarios for abrupt climate change, which have been singled out for priority research. The U.S. Climate Change Science Program released a report in late December 2008 estimating the gravity of the risk of clathrate destabilization, alongside three other credible abrupt climate change scenarios.
Loss of permafrost
Sea ice loss is correlated with warming of Northern latitudes. This has melting effects on permafrost, both in the sea, and on land. Lawrence et al suggest that current rapid melting of the sea ice may induce a rapid melting of arctic permafrost. This has consequential effects on methane release, and wildlife. Some studies imply a direct link, as they predict cold air passing over ice is replaced by warm air passing over the sea. This warm air carries heat to the permafrost around the Arctic, and melts it. This permafrost then releases huge quantities of methane. Methane release can be gaseous, but is can also be transported in solution by rivers..
Clathrate breakdown
Sea ice, and the cold conditions it sustains, serves to stabilise methane deposits on and near the shoreline, preventing the clathrate breaking down and outgassing methane into the atmosphere, causing further warming. Melting of this ice may release large quantities of methane, a powerful greenhouse gas into the atmosphere, causing further warming in a dangerous positive feedback cycle.
Even with existing levels of warming and melting of the Arctic region, submarine methane releases linked to clathrate breakdown have been discovered, and demonstrated to be leaking into the atmosphere.
According to monitoring carried out in 2003/2004 by Shakhova et al, the surface layer of shelf water in the East-Siberian Sea and Laptev Sea was supersaturated up to 2500% relative to then present average atmospheric methane content of 1.85 ppm. Anomalously high concentrations (up to 154 nM or 4400% supersaturation) of dissolved methane in the bottom layer of shelf water suggest that the bottom layer is somehow affected by near-bottom sources. Considering the possible formation mechanisms of such plumes, their studies indicated thermoabrasion and the effects of shallow gas or gas hydrates release.
Estimates of the size of the total carbon reservoir in Arctic permafrost and clathrates vary widely. There are believed to be around 400 gigatonnes of carbon in methane clathrates in permafrost regions alone.. However, Buffett and Archer predict a much higher release of between 2,000 and 4,000 gigatonnes as a result of expected human-induced warming, as they include some deep-ocean clathrate stores in the expected release.
Research 2008 in the Siberian Arctic has shown clathrate-derived methane being released through perforations in the seabed permafrost.
|
| |
|
|
