Natalia Shakhova, Igor Semiletov, and collaborators (of University of Alaska’s International Arctic Research Centre and Russian Academy of Sciences in Vladivostok) published a paper last week in Science, titled ‘Extensive Methane Venting to the Atmosphere from Sediments of the East Siberian Arctic Shelf’. They declared that the methane-rich, shallow East Siberian Arctic Shelf (ESAS), with a seafloor area of more than 772,200 square miles (three times the area of the Siberian wetlands, which are considered to be a chief source of atmospheric methane), is venting methane (the greenhouse gas) into the air and might trigger abrupt global warming.
After collecting over 5000 samples of seawater, the scientists measured the levels of dissolved methane at varying depths. High methane concentrations were observed in more than 80% of deep water and more than 50% of surface water samples, with most having concentrations more than eight times the normal amount in the Arctic Ocean. Analysing the air directly above the water surface and at higher elevations confirmed their findings. The team calculated that the region is releasing about 7 teragrams per annum (1 teragram is approximately 1.1 million tonnes), which is equal to the amount of methane emitted from the oceans (about 2% of the overall methane emissions to the atmosphere). As a result, more than 100 hotspots were located where methane is leaking from the sub-sea permafrost, which is believed to generally act as a lid to contain the methane reservoir.
When the earth becomes warm, warmer seawater enters the area. If and when the permafrost thaws, the stored frozen methane is released in two ways: Firstly, the stored organic material (ESAS, being shallow and averaging around 50 meters in depth, would have been submerged or terrestrial over the millennia) decomposes and gradually releases methane. Secondly, methane gas or methane hydrates could be released. Although methane usually oxidises into carbon dioxide before reaching the surface of deeper waters, it escapes to the atmosphere in the shallow ESAS.
The current average methane concentrations in the Arctic is around 1.85 ppm (which is the highest in 40,000 years), with much higher concentrations in ESAS- very alarming when considering that the Earth’s geological record indicates that atmospheric methane concentrations are between 0.3 to 0.4 ppm (during cold periods) and 0.6 to 0.7 ppm (during warm periods). As pointed out by Martin Heimann in his perspective in ‘Climate Change: How Stable Is the Methane Cycle?’ (in the same edition of Science), more warming in the Arctic, implies more destablisation of the permafrost, which implies more release of methane and the creation of ‘a positive feedback loop that amplifies global warming’.
Despite the current controversies in the field and the increased scepticisim about the effects of climate change, these findings might have heavy implications. A caveat is the vagueness over whether this is a new phenomenon or whether it is a constant natural phenomenon. What are the precise factors behind this? Will there be further larger release of methane? Will global warming accelerate this release? What would happen in such a scenario? Would it result in a rapid and devastating climate change, as predicted?
Additional reference:
http://www.uaf.edu/news/news/20100303192545.html
That is an enormous amount of methane, I hope it is being monitored closely! Imagine the devastating local effects of a sudden release of so much methane, even before the global atmosphere is affected.
ReplyDeleteLowering the tone slightly, It is calculated that each cow in Brazil produces about 250g of methane per day. There are an awful lot of cows and this works out (I think!) at about 14 teragrams per year!
An exceptionally valid point!
ReplyDeleteBrazil apparently has 187087000 cattle, which implies 17.19 teragrams, which is over twice the ESAS contribution!
Re: ESAS, I reckon the gravity lies in whether these emissions have been ongoing or whether it has been effected by the recent changes, and whether there is a likelihood of more release, in larger amounts.