Wednesday, February 01, 2012

Methane Gas Hydrates - Vast Energy Resource or Ecological Disaster Awaiting?

A vast and untapped resource of fuel? A contributor to global climate change? A submarine hazard and potential trigger of tsunami's? A cause of catastrophic species extinction? An ELE - Extinction of Life Event? All of these are postulated scenarios for methane gas hydrates. Methane hydrate is formed when methane gas and water are brought together under suitable conditions of low temperature and elevated pressure, such that an "ice" type structure is formed containing methane molecules in considerable quantity. It is thought that vast quantities of methane hydrate exist on the ocean beds and in the sediments of the sea floors and in permafrost, and some speculate that it might be possible to harvest the material to provide a massive reserve of methane as a fuel. Gas hydrates are among the class of materials known as "clathrates", in which guest molecules occupy cavities (pores) within a host structure. The whole field is part of what is known as "guest-host" chemistry. In a fully saturated methane-hydrate, the material holds 164 times its own volume of methane gas, but packed tightly within its confines. The hydrate provides, therefore, an effective storage unit for methane.

The temperature at which methane-hydrate is stable depends on the prevailing pressure. For example, at zero degrees C, it is stable under a pressure of about 30 atmospheres, whereas at 25 deg. C, nearer 500 atmospheres is needed to maintain its integrity. The occlusion of additional gases within the ice structure tends to add stability, whereas the presence of salts (e.g. NaCl, as from sea water) requires higher stabilising pressures. Appropriate conditions of temperature/ pressure exist on Earth in the upper 2000 metres of sediments in two regions: (i) in permafrost at high latitudes in polar regions where the surface temperatures are very low (below freezing), and (ii) submarine continental slopes and rises, where not only is the water cold (around freezing), but the pressures are high (greater than 30 atmospheres). Thus, in polar regions, methane-hydrate is found where temperatures are cold enough for onshore and offshore permafrost to be present. In offshore sediments, methane-hydrate is found at water depths of 300 - 500m, according to the prevailing bottom-water temperature. There are reported cases where "chunks" of methane-hydrate break-loose from the sea bottom and rise to the surface, depressurizing and warming, where they "fizz" from the release of methane as they decompose to the gas/water state.

There are manifold and widely disputed estimates of exactly how much methane-hydrate there is. However, a figure of 10^16 cubic metres (m^3) of methane gas occluded within the entire global deposits of this material is probably a reasonable estimate. One estimate (Dobrynin et al., in "Long-Term Energy Resources," Pitman, Boston, 1981, pp. 727-729) puts the total at nearly 10^19 m^3, but this is the only one of such magnitude. Notwithstanding, the quantities of methane-hydrate are vast, and in view of this, it is thought that it might provide a potentially significant energy source, probably at least four times the entire reserve of fossil fuels (gas, oil, coal) known (estimated). As "Peak Oil" bares its teeth, the possibility appears increasingly attractive. However, the actual extraction of methane from this source is beset by a number of difficulties: e.g. low permeability of sediments, which restrict the actual flow of methane; lack of sustained interest from the oil/gas industry (though this may well change, vide supra, according to rising pressures of demand upon the existing limited resource); current limited gas-industry infrastructure at methane-hydrate locations; and the fact that no good field example has yet been demonstrated of the successful production of methane from its gas-hydrate. All these considerations score on the negative side as far as methane-hydrate becoming a serious fuel source is concerned.

Methane is a greenhouse gas and is often cited as having a global warming potential around 20 times that of an equivalent quantity of CO2, released into the atmosphere. I am slightly at odds with this argument which seems to downplay the effect of methane, since the model assumes the release of equal volumes of methane and CO2 simultaneously, and then integrates the influence over twenty years, by which time about four-fifths of the methane will have been removed by oxidation in the Troposphere. Over the longer term, since the methane is oxidised to form carbon dioxide, the global warming effect is that of an increased burden of CO2. In my view, a more realistic model is one of "steady release" of both methane and CO2, in which case the global warming potential is equal to the "instantaneous radiative forcing constant", which is nearer 110, not 20; i.e. the global warming potential of methane is a lot worse than it is given credit for!

It seems clear that in a warming world (for whatever reason), methane will be released in increasing quantities, e.g. from warming permafrost, thus augmenting global warming. Disturbances on the sea bed may also cause the decomposition of methane-hydrate. It is known that drilling into methane hydrate poses a hazard to oil prospecting operations, and it is also thought that decomposition of methane hydrate with an eruption of methane could trigger a tsunami. More catastrophically, it is believed by some that world-scale eruptions of methane from these "ice" deposits can have triggered climate-change (global warming) on a cataclysmic level, most notably the Permian-Triassic (P-T or PT) extinction event, sometimes informally called the Great Dying, which was an extinction event that occurred approximately 252 million years ago, forming the boundary between the Permian and Triassic geologic periods. It was the Earth's most severe extinction event, which extinguished the life of up to 96% of all marine species and 70% of terrestrial vertebrae species. Because so much biodiversity was lost, the recovery of life on Earth took significantly longer than after any other extinction event, and hence it has been dubbed as the "mother of all mass extinctions."

For some time after the event, fungal species were the dominant form of terrestrial life, and perhaps this is where the planet is ultimately heading once more...


Justin said...

Chris. David Archer has published a couple of good summaries of the current literature on methane on Archer is a computational ocean chemist, a leading figure in the IPCC and one of the most respected scientists working in this field. His wiki entry is here:

The more general summary 'much ado about methane' is here:

Usually, with climate change most of the news is invariably bleak but after following the methane debate my sense is that is will not be a major player just because of the time scales involved. In Archer's words:

"In short, if there was ever a good time to provoke a hydrate meltdown it would be now. But “now” in a geological sense, over thousands of years in the future, not really “now” in a human sense. The methane hydrates in the ocean, in cahoots with permafrost peats (which never get enough respect), could be a significant multiplier of the long tail of the CO2, but will probably not be a huge player in climate change in the coming century."

Archer has also put up a simple online methane model for people to play around with here:

Explanation here:

And a worst case scenario here:

Justin said...

Methane is getting an awful lot of media attention recently, partly due to the work of Natalia Shakhova at the University of Alaska at Fairbanks. For the first time, we are starting to get some hard data on releases. A good summary is here:

Shakhova was interviewed by Skeptical Science a couple of weeks ago, so your can get her current view:

She appears a little more cautious than Archer, but also stressing that we are at the very early stages of understanding what is going on. Here is the key exchange:

"SkS: The recent reports of substantial releases of methane on the ESAS prompt us to ask how these observed emissions could detectably change global atmospheric methane concentrations and in what timeframe?

NS: To date, we have only taken the very first steps down the long path of learning enough to answer this question. We officially reported only 8 Tg of methane was being released from the ESAS per year. This reported amount is <2% of the total annual global methane release and would not detectably change global atmospheric methane concentrations. However, we did not incorporate a few emission components – probably the most important ones - because of some uncertainties still remaining concerning their constraints. Newly obtained data, without question, indicate that annual methane emissions from the ESAS have been underestimated. To say how significant the underestimated components are, and to identify the mechanisms responsible for such substantial releases, we need to carefully analyze obtained data and, very likely, conduct further investigations on a broader scale. To be able to answer your question, which is a core question of our study as well, we need to establish at least a few observatory sites to trace dynamic atmospheric concentrations of methane; we need to develop a monitoring net to detect changes occurring in known plume areas; we also need to continue all-season observations in this region to study temporal and spatial variability in methane releases and the factors that determine this variability. We undoubtedly need to learn much more than we currently know. We call for the involvement of serious funding organizations to give this study the level of support that is consistent with the importance of this topic."

Justin said...

Skeptical Science also did a great methane background covering her work before the interview here:

Chris Rhodes said...

The danger with media promulgation of stories with the messages of "we can't do anything about peak oil/carbon emissions etc., and there's no point anyway because all this methane is being released and so we are doomed" is that this will become a self-propelled legacy. The forces of apathy are overwhelming!

But whatever actions we need to take as a human society we need to begin them now.