Questions and Answers on Potentially Large Methane Releases From Arctic, and Climate Change
Sub-sea permafrost is losing its ability to be an impermeable cap
March 4, 2010
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For more information, see the press release: Methane Releases From Arctic Shelf May Be Much Larger and Faster Than Anticipated.
What is methane?
Methane is a naturally-occurring compound that is created when organic material, such as the remains of plants and animals, rot or otherwise break down. Bacteria and other microbes play a large role in processes that produce methane. These methane-producing processes may, for example, occur in landfills as their contents age. And some animals release methane as their bodies digest their food.
Vast stores of methane are trapped in the permafrost of the Arctic--large swaths of land where the ground stays frozen. Because of climate change, some Arctic permafrost is showing signs of thawing. This thawed Arctic permafrost may release methane into the atmosphere.
Why does methane cause so much concern?
Like carbon dioxide, methane is a greenhouse gas. The presence of greenhouse gases in the atmosphere inhibits the Earth's heat from being released into space. Therefore, increased levels of greenhouse gases in the atmosphere may cause the Earth's temperature to increase over time.
Methane may be "stored" underground or under the seafloor as methane gas or methane hydrate; methane hydrate is a crystalline solid combining methane and water, which is stable at low temperatures and high pressure--conditions commonly found in marine sediments. When methane stores are released relatively quickly into the atmosphere, levels of atmospheric methane may rapidly spike.
As a greenhouse gas, methane is 30 times more potent (gram for gram) than carbon dioxide. This means that adding relatively modest amounts of methane to the atmosphere may yield relatively large impacts on climate.
THE NEW Science STUDY
Who conducted the study?
The study was conducted by an international team of researchers led by Natalia Shakhova and Igor Semiletov--both from the University of Alaska Fairbanks. The study was partially funded by the National Science Foundation.
Where is the Shakhova and Semiletov study published?
The study appears in the March 5, 2010 issue of Science.
How much methane does it take to increase warming?
There's no clear answer to that question. However, the Earth's geologic record indicates that atmospheric concentrations of methane have varied from about 0.3 to 0.4 parts per million during cold periods to about 0.6 to 0.7 parts per million during warm periods.
The Shakhova and Semiletov study indicates that methane levels in the Arctic now average about 1.85 parts per million, the highest level in 400,000 years.
How much methane is currently being released from the East Siberian Arctic Shelf?
The Shakhova and Semiletov study suggests that 7 teragrams of methane are currently being released annually from the East Siberian Arctic Shelf. That's about equal to the amount of methane that is annually released from the rest of the world's oceans combined, and much more than was previously believed to be released from that part of the Arctic. What's more, the study raises the possibility that methane releases from the East Siberian Arctic Shelf could rise dramatically as its permafrost cover is thawed by warming temperatures.
What are the mechanisms that release methane in the East Siberian Arctic?
Methane may be released in two ways:
- Organic material is contained in soil that is frozen into permafrost. This permafrost thaws as the Earth warms. When the organic matter in this thawing permafrost begins to decompose under anaerobic conditions, it gradually releases methane.
- A subsea layer of permafrost covers a layer of seabed methane--stored as methane gas or methane hydrates. The subsea permafrost layer has long served as a barrier to the methane, sealing it in the seabed. But warming waters have begun to melt this subsea permafrost. The result: destabilization and perforations in the permafrost that create pathways for releases of underlying methane. Such releases may be larger and more abrupt than those that result from decomposition.
Why wasn't this phenomenon predicted before? Why is it a surprise?
The East Siberian Arctic shelf is a relatively new frontier in methane studies. Earlier studies in Siberia focused on methane seeping from thawing terrestrial permafrost.
Nevertheless, the existence of methane releases from the East Siberian Arctic Shelf itself isn't a surprise; in fact, the Shakhova and Semiletov study was conducted precisely because this phenomenon was, in some ways, predicted. What is a surprise about the study results is the magnitude of methane releases and the fact that they already happening on such a scale.
Does methane released in the Arctic only warm the Arctic?
No. Once subsurface methane is released and enters the atmosphere, it may circulate all over the Earth. Also, because the Arctic has a special influence on global climate, increasing Arctic temperatures contribute to global climate change and global rises in sea level.
Henrietta Edmonds, National Science Foundation, (703) 292-8029, email: email@example.com
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