Methane
Posts Tagged ‘Methane’
If you read Frank Schätzing’s “Der Schwarm” you will have an idea about the potential catastrophic effects of the melting of methane hydrates. So what are methane hydrates and why is their melting so worrisome?
Methane hydrates are compounds that trap large amounts of methane inside the crystal structure of frozen water. These compounds are commonly found in shallow areas of the ocean within the sediments as well as right on the ocean floor all over the world’s continental shelves (see figure above). They are stable at 0°C, but under pressure (such as underneath the ocean surface) they can be stable at higher temperatures. Methane hydrates used to be stable at a depth of about 100 to 400 m, in a zone called “gas hydrate stability zone”. However, this stability zone is shifting downwards as ocean temperatures are increasing from anthropogenic global warming. Consequently, methane hydrates that are deposited at relatively low water depths start to become unstable.
A recent article in Geophysical Research Letters by Westbrook et al. describes this worrisome behavior: more than 250 gas bubbles, predominantly containing methane, have emanated from the seabed of the West Spitzbergen continental margin, from depths between 150 to 400 m.
The reason for the destabilization of methane hydrates in this area is probably the great increase in ocean temperature in this region: the northward flowing West Spitzbergen current has warmed by 1°C just during the last 30 years . This increase is huge compared to the global increase in ocean temperature which is less than half of the air temperature, thus less than 0.5°C.
As water temperatures increase, methane hydrates become unstable and break down into water and methane. The methane gas then bubbles up towards the surface of the ocean. Currently, the bubble dissolves before it reaches the air, thus not yet directly contributing to an addition of greenhouse gases to the atmosphere. However, the dissolving of methane in water further decreases its acidity which can severely affect ocean life (see previous article).
If the bubble would reach the ocean surface, then it would release methane into the atmosphere. Because methane is a greenhouse gas 20 times more potent than carbon dioxide, the release of vast amounts of methane can significantly contribute to the acceleration of global warming. Methane has a relatively short half-life in the atmosphere of seven years (compared to several 100 or even 1000 years for CO2). However, methane is oxidized to CO2 and water, thus further contributing to global warming even after it is broken down. A release of methane from methane hydrates is therefore, like the release of methane from permafrost, a very serious threat to our current global climate. In fact, sudden releases of large amounts of methane are associated with significant changes in the earth’s climate at former periods, such as the Permian-Triassic extinction.
As described in ScienceDaily, Graham Westbrook Professor of Geophysics at the University of Birmingham, warns: “If this process becomes widespread along Arctic continental margins, tens of megatonnes of methane per year – equivalent to 5-10% of the total amount released globally by natural sources, could be released into the ocean.”
Maiken Winter
Beitrag Bookmarken:
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Northern peatlands – waterlogged areas that accumulate large amounts of organic materials in its soils – cover only 2% of the [mehr...]
Fig. 1. Thawing permafrost. Image credit – Edward A.G.Schuur, University of Florida
Permafrost is a subject in the climate change debate I have tried to not think about too much. It is just too scary to think about the vast amounts of carbon stored in frozen soils, ready to be released if global temperatures keep rising. But it seems to be [mehr...]
But why is the decomposition of organic material so worrisome? Decomposition means that an object is falling into its parts. And a large part of the decomposing organic material stems from plants. To really understand what is happening in the Arctic we therefore need to shortly take a look at photosynthesis (Fig. 2):
Plants take up water and carbon dioxide, add a bit of sunlight and nutrients, and assemble all this during the absolutely amazing process of photosynthesis into a completely new structure: sugar, with the “waste product” of oxygen.
Fig. 2. Photosynthesis and decomposition. Picture from Wikipedia
In reverse, during decomposition sugar molecules and oxygen react with enzymes that decompose sugar to water and CO2; or, under unaerobic circumstances (i.e., without oxygen, such as in soils underneath lakes), the sugar molecules decompose into other molecules, including methane (CH4). Both CO2 and methane are very potent greenhouse gases. The thawing of permafrost thus releases vast amounts of greenhouse gases.
Fig. 3. Measured (1995-2003) and calculated (1930-1995) averaged over the year soil temperatures in Fairbanks, Alaska area
But is permafrost thawing already? You bet it does. Indeed, in some areas permafrost has warmed by up to 3ºC within the last decades (Fig. 3). In some areas, temperatures of the permafrost are getting dangerously close to above freezing. In fact, in some areas, soil temperature has already passed the thawing point (see references at NOAA) .
Just how much organic material is stored in the permafrost has so far been “hugely under-estimated.” A new report indicates that the amount of carbon stored in permafrost around the North-Pole might bee twice as high as previously thought (CSIRO).
Executive Director of the Global Carbon Project at CSIRO, Dr Pep Canadell, mentioned that
“Projections show that almost all near-surface permafrost will disappear by the end of this century exposing large carbon stores to decomposition and release of greenhouse gases.”
According to these new estimates, a thawing of about 10% of the Arctic soil would release about 80 ppm CO2. Global temperature would then increase on abverage by about o.7ºC.
Considering
- that we are already above the CO2 concentration that is considered relatively safe for the future of human civilization (350 ppm CO2)
- that in June 2009 we reached 390 ppm CO2
- that a global increase in temperature above 2ºC will likely cause the passing of irreversible tipping points, and
- that we are already almost committed to a global increase in temperature to 2ºC,
this estimate is extremely worrisom – to say the least.
Even though it is important to clearly understand what will happen if we do not act in time, let’s not worry too much about what could happen in case of inaction. Instead, let’s focus on what we need to work towards:
We need a carbon free energy future which is exclusively supported by truly renewable energies like the sun, wind, water, and geothermy within the coming decades. Such a “Great Transformation” will only be possible with vast energy savings through energy efficiency and through a change in our behavior, wasting much less energy than we do now. We must not be satisfied with half measures. Without effective fast action, all our efforts will likely be to no prevail.
Maiken Winter
More information:
http://www.csiro.au/news/Permafrost-climate-change-threat.html
http://www.reuters.com/article/africaCrisis/idUSSP458218
http://www.arctic.noaa.gov/essay_romanovsky.html
