Note that Archer describes ocean clathrate degeneration as predominantly 'Chronic not catastrophic', although individual slumping/destabilisation events are locally catastrophic, leading to the sudden releases described. The main influence on global climate from decomposition of deep deposits is the addition of CO2 to the atmosphere, as the release is not fast enough for methane to be the principle actor. This buys us extra time for geoeng.
http://en.wikipedia.org/wiki/Runaway_climate_change#Current_risk Lawrence et al(2008) suggests that a rapid melting of the sea ice may up a feedback loop that rapidly melts arctic permafrost.[36]<http://en.wikipedia.org/wiki/Runaway_climate_change#cite_note-35> [37] <http://en.wikipedia.org/wiki/Runaway_climate_change#cite_note-36> However, ocean clathrates are expected to destabilise much more slowly.[38]<http://en.wikipedia.org/wiki/Runaway_climate_change#cite_note-37> Estimates of the size of the total carbon reservoir in Arctic permafrost<http://en.wikipedia.org/wiki/Permafrost> and clathrates <http://en.wikipedia.org/wiki/Clathrates> vary widely. It is suggested that at least 900 gigatonnes of carbon in permafrost exists worldwide.[39]<http://en.wikipedia.org/wiki/Runaway_climate_change#cite_note-38> [*citation needed <http://en.wikipedia.org/wiki/Wikipedia:Citation_needed>*]. Further, there are believed to be around and another 400 gigatonnes of carbon in methane clathrates in permafrost regions alone.[40]<http://en.wikipedia.org/wiki/Runaway_climate_change#cite_note-39>. Should this estimate of volume be correct or at least too low, and if clathrates are omitted from the analysis completely, then 900 gigatonnes of carbon may potentially be released as methane as a result of human activity. Methane <http://en.wikipedia.org/wiki/Methane> is a potent greenhouse gas <http://en.wikipedia.org/wiki/Greenhouse_gas> with a higher global warming potential <http://en.wikipedia.org/wiki/Global_warming_potential> than CO2 <http://en.wikipedia.org/wiki/CO2>. The global carbon reservoir in ocean clathrates is estimated in the range 10,000-11,000 gigatonnes.[41]<http://en.wikipedia.org/wiki/Runaway_climate_change#cite_note-40> Archer[42]<http://en.wikipedia.org/wiki/Runaway_climate_change#cite_note-41> notes that according to the reservoir estimates used in his own paper that: The hydrate reservoir is so large that if 10% of the methane were released to the atmosphere within a few years, it would have an impact on the Earth's radiation budget equivalent to a factor of 10 increase in atmospheric CO2. However, his paper suggests that the great majority of such a release is likely to be chronic, rather than catastrophic, and that 21st-century effects are therefore likely to be 'significant but not catastrophic'. It is further noted by Kvenvolden[43]<http://en.wikipedia.org/wiki/Runaway_climate_change#cite_note-42> that 'much methane from dissociated gas hydrate may never reach the atmosphere', as it can be dissolved into the ocean and broken down biologically. Other research[44]<http://en.wikipedia.org/wiki/Runaway_climate_change#cite_note-43> clearly demonstrates that a release to the atmosphere can occur during large releases. These sources suggest that the clathrate gun<http://en.wikipedia.org/wiki/Clathrate_gun> effect alone will not be sufficient to cause the effects that Archer envisages as 'catastrophic' within a human lifetime. A slow release of methane<http://en.wikipedia.org/wiki/Methane> chiefly affects global warming <http://en.wikipedia.org/wiki/Global_warming> by increasing the CO2 <http://en.wikipedia.org/wiki/CO2> levels in the atmosphere, rather than by direct action.[45]<http://en.wikipedia.org/wiki/Runaway_climate_change#cite_note-44> see also: http://en.wikipedia.org/wiki/Clathrate_gun_hypothesis 2009/2/8 dsw_s <[email protected]> > > "The absence of a δ13C gradient in the water column during these > events implies that the methane rose through the entire water column, > reaching the sea-air interface and thus the atmosphere. Foraminiferal > δ18O composition suggests that the rise of the methane in the water > column created an upwelling flow. These inferred emission events > suggest that during the last glacial episode, this process was likely > widespread, including tropical regions." > http://www.pnas.org/content/101/25/9187.abstract > > People only ever talk about arctic clathrates, but this from 2004 says > tropical too. I don't have full-text access. Can someone post full > text or relevant excerpts, or explain what's new if this is out of > date? > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en -~----------~----~----~----~------~----~------~--~---
