Arctic methane release - AbsoluteAstronomy.com

Arctic methane release is the release of methane

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 seas and soils in 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...

regions of the Arctic

Arctic

The Arctic is a region located at the northern-most part of the Earth. The Arctic consists of the Arctic Ocean and parts of Canada, Russia, Greenland, the United States, Norway, Sweden, Finland, and Iceland. The Arctic region consists of a vast, ice-covered ocean, surrounded by treeless permafrost...

, 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

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...

. This results in a weak positive feedback

Positive feedback

Positive feedback is a process in which the effects of a small disturbance on a system include an increase in the magnitude of the perturbation. That is, A produces more of B which in turn produces more of A. In contrast, a system that responds to a perturbation in a way that reduces its effect is...

effect, as methane

Methane

is itself a 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...

. The feedback is weak, however, because methane is well-mixed globally: the local release leads to a warming spread over the whole globe.

The Arctic region is one of the many minor natural sources of the greenhouse gas methane. Global warming may accelerate its release, due to both release of methane from existing stores, and from methanogenesis

Methanogenesis

Methanogenesis or biomethanation is the formation of methane by microbes known as methanogens. Organisms capable of producing methane have been identified only from the domain Archaea, a group phylogenetically distinct from both eukaryotes and bacteria, although many live in close association with...

in rotting biomass

Biomass

Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....

. Large quantities of methane are stored in the Arctic in natural gas deposits, permafrost, and as submarine clathrates

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...

. Permafrost and clathrates degrade on warming, thus large releases of methane from these sources may arise as a result of global warming. Other sources of methane include submarine 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, river transport, ice complex retreat, submarine permafrost and decaying gas hydrate deposits.

During interglacials, average atmospheric methane

Atmospheric methane

Atmospheric methane levels are of interest due to its impact on climate change. Atmospheric methane is one of the most potent and influential greenhouse gases on Earth. The 100-year global warming potential of methane is 25, i.e...

concentrations are nearly twice the lowest values in the depths of glacial. Concentrations in the Arctic atmosphere are higher by 8–10% than that in the Antarctic 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." Soil temperature and moisture levels have been found to be significant variables in soil methane fluxes in tundra

Tundra

In physical geography, tundra is a biome where the tree growth is hindered by low temperatures and short growing seasons. The term tundra comes through Russian тундра from the Kildin Sami word tūndâr "uplands," "treeless mountain tract." There are three types of tundra: Arctic tundra, alpine...

environments.

According to R. A. Kerr, while methane release is indeed likely to amplify global warming, fears that it could lead to catastrophe are likely overblown.

Contribution to climate change

The release of methane from the Arctic is in itself a contributor to global warming

Global warming

as a result of arctic shrinkage

Arctic shrinkage

Ongoing changes in the climate of the Arctic include rising temperatures, loss of sea ice, and melting of the Greenland ice sheet. Projections of sea ice loss suggest that the Arctic ocean will likely be free of summer sea ice sometime between 2060 and 2080, while another estimate puts this date at...

. Recent observations in the Siberian arctic show increased rates of methane release from the Arctic seabed. 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.

However the significant measure from the viewpoint of global warming and the radiative forcing

Radiative forcing

In climate science, radiative forcing is generally defined as the change in net irradiance between different layers of the atmosphere. Typically, radiative forcing is quantified at the tropopause in units of watts per square meter. A positive forcing tends to warm the system, while a negative...

is the global atmospheric methane concentration. As the figure shows, increases of methane have slowed significantly over the past decade, and any contribution from Arctic release is not large enough to affect this global picture.

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

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.

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

Abrupt climate change

An 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...

, 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

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. NewScientist states that "Since existing models do not include feedback effects such as the heat generated by decomposition, the permafrost could melt far faster than generally thought."

There is another possible mechanism for rapid methane release. As the Arctic ocean becomes more and more ice free, the ocean absorbs more of the incident energy from the sun. The Arctic ocean becomes warmer than the former ice cover and much more water vapour enters the air. At times when the adjacent land is colder than the sea, this causes rising air above the sea and an off-shore wind as air over the land comes in to replace the rising air over the sea. As the air rises, the dew point is reached and clouds form, releasing latent heat and further reinforcing the buoyancy of the air over the ocean. All this results in air being drawn from the south across the tundra rather than the present situation of cold air flowing toward the south from the cold sinking air over the Arctic ocean. The extra heat being drawn from the south further accelerates the warming of the permafrost and the Arctic ocean with increased release of methane.

Clathrate breakdown

Sea ice

Sea ice is largely formed from seawater that freezes. Because the oceans consist of saltwater, this occurs below the freezing point of pure water, at about -1.8 °C ....

, and the cold conditions it sustains, serves to stabilise methane

Methane

deposits on and near the shoreline, preventing the clathrate breaking down and outgassing methane

Methane

into the atmosphere, causing further warming. Melting of this ice may release large quantities of methane

Methane

, a powerful greenhouse gas

Greenhouse gas

into the atmosphere

Atmosphere

An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...

, causing further warming in a strong positive feedback

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

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

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.

Research 2008 in the Siberian Arctic has shown clathrate-derived methane being released through perforations in the seabed permafrost.

The climatic effects of a potential release of methane from ocean clathrates may be significant on timescales of 1–100 thousand years.

External links

Methane hydrates and global warming RealClimate from December 12, 2005

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Contribution to climate change

Loss of permafrost

Clathrate breakdown

See also

External links