Tuesday, September 23, 2008

Global Warming from Melting Permafrost?

It was reported this morning in the Independent newspaper that massive amounts of methane are bubbling up from the Arctic depths as sub-sea permafrost in sediments melts. The essential principle is methane hydrate, a compound of methane and ice which only exists under particular conditions of cold and pressure. As the Arctic warms the waters are no longer sufficiently cold to preserve the material which thus decomposes into methane gas and water.

It has been speculated on that some abrupt and profound changes in the past climate, including the wholesale extinction of species, are down to the sudden collapse of methane hydrate and extreme greenhouse-warming from methane gas in the atmosphere. It is often quoted, as in the Independent today, that methane is "a greenhouse gas 20 times more potent than carbon dioxide ", but this is the case averaged over a 100 year period. Over 20 years, it is 60 times more potent, and if say one kilogramme each of methane and carbon dioxide were released simultaneously into the atmosphere, the global warming potential of methane is nearer 100 times that of CO2.

The latter figure may be deduced as follows from the definition for Global warming potential in: http://en.wikipedia.org/wiki/Global_warming_potential - along with some factors for atmospheric lifetimes for CH4 and CO2 (the latter is quite variable, between 50 and 200 years). From the data in that link, if the warming potential (relative to CO2) for methane is 7 (over 500 years), 23 (100 years), 62 (20 years) - (or the other set of data given) a value of 100 (as deduced below) is reasonable for zero-years, i.e. instantaneous radiative forcing by a given mass of each gas.

Taking the equation that defines GWP (x) in the above link, and then reducing it for t=o (TH=0), you get:

GWP(CH4) = aCH4/aCO2 x MWCO2/MWCH4 = .53W/m^2 ppmv/.015W/m^2 ppmv x 44/16 = 97.2. i.e. about 100. The point is that it's one kg of each gas (i.e. mass not volume) that is assumed to be added to the atmosphere. Since the volume of a kg of a gas depends on the MW of its molecules you need the correction factor as shown, i.e the volume of a kg of CO2 is less than that of a kg of CH4 by the factor of 16/44.

Both gases will over time be removed from the atmosphere, with lifetimes of about 12 years for methane and about 100 years for CO2 (depending on where it is), but I am assuming a kind of steady-state situation where both gases are continually contributed, as seems to be the case, although the amounts of each may vary over time. However, the latter case is complex and goes beyond this simple definition of GWP.

The point is that in terms of assessing the relative GWP of gases relative to CO2, it is important to note the time interval that is being quoted.

Furthermore, if methane is being emitted at up to 100 times background levels in hot-spot regions of the Siberian continental shelf, and the GWP is 100 that of CO2, the effect of this could be catastrophic and climate models will need to be amended to include its influence.

This may well be a striking example of a feedback mechanism in the earth system, where more warming releases more methane and the system runs-away, leading to unexpectedly high, at least local, temperatures with profound influences on the climate of particular regions as the earth heat-machine is tuned in the way it redistributes heat from the equatorial and tropical regions toward and around the poles.

One explanation for the release of methane from the Arctic is that there is an increasing volume of relatively warm water being disgorged from Siberia's rivers as the land-based permafrost melts there. Overall, the Arctic region has felt a rise in temperature of 4 degrees C during the past few decades, with a concomitant decrease in the area of sea-ice there. A significant body of scientists anticipate that the loss of sea-ice which normally reflects sunlight, will result in yet warmer temperatures as the energy is instead absorbed by the open sea.

"Exclusive: The methane time bomb." By Steve Connor. http://www.independent.co.uk/news/science/exclusive-the-methane-time-bomb-938932.html

dobermanmacleod said...

I predict that natural methane emissions from melting methane hydrate will overwhelm any cuts we make to our emissions:

A frozen peat bog in western Siberia the size of France and Germany put together contains about 500 billion tons of carbon. Western Siberia has warmed faster than almost anywhere else on the Earth, with an increase in average temperature of about 3C in the last 40 years.

Even more Siberian permafrost is under the ocean, an area six times the size of Germany containing about 540 billion tons of carbon. That submarine permafrost is perilously close to thawing. Three to 12 kilometers from the coast the sea sediment is just below freezing. The permafrost has grown porous, there is a loss of rigor in the frozen sea floor, and the surrounding seawater is highly oversaturated with solute methane.

“If the Siberian (submarine) permafrost-seal thaws completely and all the stored gas escapes, the methane content of the planet's atmosphere would increase twelve fold. The result would be catastrophic global warming.” --"A Storehouse of Greenhouse Gases Is Opening in Siberia," Spiegel, 17 April '08

Professor Chris Rhodes said...

You make a compelling case, Brad!

So, what do you propose we should do? If we can't do much about the overall global warming influence of CO2 because it will in nay case be out-stripped by methane release from a warming world, do we just give up and accept our fate?

I recall that Lovelock concluded a while ago to the effect that we should just enjoy life while we can and accept the tough environmental consequences to come!

If humanity really is terminally sick, maybe we should just enjoy the day!

Regards,

Chris.

Anonymous said...

Astonishing really that no-one in the world of politics seems to be paying attention to this issue.

Governments and corporations seem to delight in finding phony solutions to the global warming issue that offer either political Kudos or prospects for profit, but ignore almost entirely any low tech solutions that offers some practical prospect of working.

The only proposal i see that addresses the issue of permafrost is from the left-field ecologist in Eastern Siberia who proposes the re-introduction of mega fauna to the steppe. His argument, though unproven, is that in the holocene northern Russia supported grassland which was eliminated as a result of the disappearance of mega-fauna. His details can be found at http://www.faculty.uaf.edu/fffsc/park.html.

Unfortunately such low-tech solutions with quite plausible outcomes are almost entirely ignored, while simplistic but superficially attractive notions incapable of scaling to the impact required to make a sizeable difference are given great attention - low energy light bulbs, wind-farms - attract generous financial and political support.

Perhaps the European nations should suggest to the Russians that we will only continue to import Russian gas if they urgently fund such creative approaches to the Siberian permafrost problem.

Professor Chris Rhodes said...

Hi Steve,

maybe there is less political mileage in looking at such "natural" solutions to carbon emissions when the real reason for low-carbon strategies is to use less of the carbon-fuels, especially oil, that we are likely to run short of in the near future?

The approach by this Russian fellow seems to be something like regenerative agriculture which it is thought could reduce the atmospheric burden of carbon by up to 4 Gt (billion tonnes) per year.

I have a later posting called "Thinking Positive - carbon capture" (I also put it on scitizen.com)which refers to various "natural carbon capture schemes, but I concede that to bring them all on the grand-scale will take colossal amounts of engineering.

The possible exception to that is biochar (to make terra pretta) which if made on the scale of millions of small communities could wrap-up maybe one Gt annually in total.

Best regards,

Chris.

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