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Should We Fear the Methane Time Bomb (Part Deux)?
Climate alarmists have long warned that warming of the Arctic could melt frozen marine and permafrost sediments, releasing methane trapped in peat bogs and ice crystals (clathrate hydrates, see photo above). Methane is a potent greenhouse gas that packs 21 times the global warming punch as CO2 over a 100-year time span and more than 100 times the CO2-warming effect over a 20-year period.
So the fear is that methane emissions from the thawing Arctic will accelerate global warming, which in turn will melt more calthrates and methane-bearing sediments, which will produce still more warming, in a vicious circle of climate destabilization. In a previous post, I offered a skeptical perspective on this doomsday scenario.
This week the journal Nature published a study raising similar concerns about the potential for significant releases of methane from the Antarctic ice sheets. The study’s 14 authors, led by Jemma Wadham of the University of Bristol in the UK, estimate that about 21,000 petagrams (gigatons) of organic carbon (OC) are buried in sedimentary basins buried under the East and West Antarctic ice sheets – more than 10 times the estimated magnitude of OC stocks in northern permafrost regions. Microbial production of methane from OC (a process known as methanogenesis) is common across many cold subsurface environments, and may have been at work for millions of years beneath the Antarctic Ice Sheets.
Although “No data exist for rates of methanogenesis in sub-Antarctic marine and terrestrial sediments,” the model used by the Wadham team indicates the potential hydrate reserve could be 70–390 petagrams of carbon (PgC) beneath the East Antarctic Ice Sheet (EAIS) and tens of PgC beneath the West Antarctic Ice Sheet (WAIS). ”This represents a sizeable reservoir of methane hydrate, of a similar order of magnitude to more recent estimates of Arctic permafrost and Arctic ocean hydrate reserves,” the authors state. They contend that subglacial hydrate deposits are likely to be located at shallow depths, “highlighting the strong potential for deglaciation to trigger hydrate destabilization.”
The researchers conclude that “the Antarctic Ice Sheet may be a neglected but important component of the global methane budget, with the potential to act as a positive feedback on climate warming during ice-sheet wastage.”
Well, kudos to Wadham and her colleagues for not injecting apocalyptic rhetoric into a scientific paper. Nonetheless, the paper is attracting media coverage (e.g. here and here) because it raises the possibility of a significant new ‘positive feedback’ that dramatically accelerates global warming.
I wouldn’t lose any sleep about this even if ”deep drilling” later validates the researchers’ estimates of the quantity of hydrates lying beneath the Antarctic Ice Sheets.
Ice core data obtained from the Russian Vostok station in East Antarctica do show a strong correlation over the past 420,000 years between changes in global temperature and atmospheric levels of both CO2 and methane. The data, however, also indicate that two previous interglacial periods were warmer than the Holocene.
Clearly, warming periods release large quantities of methane trapped in frozen marine and terrestrial sediments. Yet in none of the previous interglacials — including the two that were warmer than the present — did warming produce a self-perpetuating, climate de-stabilizing spike in atmospheric methane levels.
The greenhouse effect did not gallop away. Global temperatures largely determined methane levels, not the other way around. Even greater-than-present warmth did not turn Antarctica’s OC deposits into a climate-disrupting methane bomb.
2012-08-31 14:54:38
Source: http://www.globalwarming.org/2012/08/31/should-we-fear-the-methane-time-bomb-part-deux/
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