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Earthtribe-Gather: Moonlight through Leaves |
Category: Diary 2 comments
28 May 2005 @ 02:36 by koravya : Dark Night 28 May 2005 @ 21:30 by koravya : More on Methane Selected paragraphs from Chapter five of KILLER IN OUR MIDST Methane Catastrophes in Earth's Past and Near Future [link] 5. METHANE CATASTROPHE (Continental Margin Methane Release) [link] What Erwin missed was the importance -- indeed, the indispensibility -- of the rapid increase of these gases for the transformation of global climate and marine chemistry. (The rate of release is crucial. A truck, moving at 100 kilometers, or sixty miles, per hour, can be extremely dangerous to things in its path; at a meter -- yard -- per hour, the truck would constitute little or no danger. Just as the truck's potential threat depends on its momentum and therefore its speed, so also does the ecological impact of methane and carbon dioxide depend on their ecological momentum, or rate of increase. The faster the delivery, the harder the blow.) . . . Global Warming But the most important consequence of a colossal methane release would have been the warming of the planet by the greenhouse gas methane and its successor, carbon dioxide. We tend to underestimate the impact of global warming on other organisms. . . . the impact of global warming has been popularly assumed to be something which will only gradually encroach upon other organisms, and cause extinction only in unusual circumstances. Instead, habitat destruction has generally been presumed to be the major human activity which will adversely affect our fellow species. . . . We no longer have any excuse for such naiveté. A careful examination of a large number of species in numerous parts of the planet projects that a stunning portion of them will be "'committed to extinction'" in just 50 years, with only modest global warming (Thomas, 2004). It does not mean that 50 years from now all these "committed" species will be gone, but rather that they will no longer have a habitat in which they can survive. The demise of the last members of such species may hang on for some decades, but their ultimate doom is assured. In 50 years, more than 10% of terrestrial species -- at minimum -- will be on a one-way path to extinction; in 100 years, almost all those species will be gone. . . . The message of this study is simple: climate change kills -- and kills extraordinary numbers of living things -- even when it is minor. . . . Cloud cover would have increased, but the role of clouds in determining climate is a matter of continuing discussion and much serious investigation among scientists, because clouds both increase Earth's albedo (thus reflecting more solar radiation back into space) and cooling the planet, and increase the amount of warmth beneath them. It is still unknown whether, on balance, clouds contribute more to planetary warming or cooling, though the answer is sure to be different for different types of clouds. . . . While the initial triggering mechanism is different -- the anthropogenic production of carbon dioxide in the present versus direct oceanic warming and indirect CO2-induced global warming caused by Traps volcanism at the end of the Permian -- the effects would have been the same. The atmosphere warmed, and the ocean and the terrestrial surface with it. Huge numbers of species were not able to survive the changed conditions, and they died. . . . The term "dissociation" refers to the breakup of the clathrate structure of the hydrate, those icy lattices that contain the methane. Once these lattices dissolve, the methane is released. Small amounts of methane are always being released through dissociation; massive dissociation refers to significant breakup of the clathrates, and a major release of methane. This can occur only by the warming of the sediments, or by their depressurization caused by a fall in sea level. . . . Methane hydrate can cause or contribute to the instability of continental margins and the likelihood of submarine landslides in several ways. . . . The association between hydrate dissociation and slumping, in fact, was one of the first dangers of seafloor hydrates to be recognized, now almost thirty years ago (McIver, 1977). Not surprisingly, slumping is the most abrupt and potentially catastrophic of the various modes of methane release. . . . Continuous and Episodic versus Catastrophic Release: Certain of the release modes of continental margin methane are more or less continuous, and seem to represent the usual way that methane is released from margin sediment. These modes are trickling and rafting, though rafting is a very minor release mode and only attracts attention because of its startling unfamiliarity. Sediment waves presumably develop regularly in various parts of the world ocean seafloor over long periods of time, and their methane likely is also released gradually. Venting occurs episodically, as free methane pressure builds in sediment and then forces its way out through faults or such other fluid release structures as pockmarks. Mud volcanism is an occasional, local phenomenon that periodically injects small quantities of methane into the ocean and atmosphere. The remaining two modes allow for catastrophic release. . . . Submarine landslides Massive landslides are among the most rapid and destructive geological processes on the planet. But since submarine landslides are not visible to the unaided eye -- and in the murky depths of the ocean can only be seen and photographed in tiny areas which provide no clue as to their real extent -- a comparison with a highly visible terrestrial landslide may be useful. . . . An estimated 350 billion metric tons of methane was released in these slide events, both from dissociated methane hydrate and the free gas that lay below them. This amount of methane contains some 263 billion metric tons of carbon, equivalent to about 1/3 the total carbon in the atmosphere, making its release roughly equivalent to the amount of anthropogenic carbon released into the atmosphere since the beginning of the industrial age. . . . Though other suggested scenarios for the cause of the end-Permian extinction may be found to be compatible with these time estimates, it is only the margin methane proposal which independently generated such timelines (based on the LPTM and computer modeling), and enjoys several independent lines of support by way of confirmation. . . . By contrast, large-scale methane release can indeed produce serious global consequences. It has great potential as a greenhouse gas for warming the planet, and, of course, it is quickly oxidized to carbon dioxide. Thus, for warming the planet, large quantities of methane are an excellent, readily-available resource. In addition, that methane has the ability to directly cause oceanic anoxia, and to reduce the level of atmospheric oxygen by interfering with the activity of marine and terrestrial photosynthesizers. Therefore, methane has the potential to produce more significant, global, and protracted consequences for Earth's organisms than did Siberian Traps volcanism alone. . . . Recently there have been a number of new and revived proposals regarding the cause(s) of the end-Permian extinction. . . . The first of these theories starts with an allegedly anoxic ocean. The anoxia allows methane to reach, or almost reach, saturation levels (where the seawater has as much dissolved methane as it can hold) in the ocean. Then, perhaps triggered by an earthquake, volcano, warm current, or other disturbance -- or without any external cause at all -- this gas suddenly erupts from the ocean, much like soda from a shaken pop bottle. Ignited by lightning, the methane devastates life on land, and the Earth is plunged either into a period of cooling (caused by sun-obscuring firestorms) or warming (caused by the increased carbon dioxide in the atmosphere)(Ryskin, 2003). . . . The evidence we now have regarding end-Permian events, and their connection to the end-Permian extinction seem quite adequate to explain that extinction. Traps volcanism initiated the process, helping shut down thermohaline circulation and warming the globe, including releasing continental margin methane. The methane release completed the transition to anoxia in the deeper ocean, and contributed to hypoxic conditions in coastal areas. The increased acidity of rainfall, ocean-eutrophying volcanic ashfalls, and occasional bursts of hydrogen sulfide from the shallow seafloor made additional contributions to the increasingly unpleasant and inhospitable ecological conditions. Most important, however, was the rise of global temperatures, initiated by carbon dioxide from Traps volcanism, and followed by the high atmospheric levels of methane and its successor greenhouse gas carbon dioxide. The new projections of the near-future impact of current global warming indicate that even the heating of the planet by a few degrees can have extremely lethal consequences (Thomas, 2004). What other killing mechanisms are necessary? None. *-/_* Other entries in Diary 31 May 2008 @ 05:23: Turquoise 13 Feb 2008 @ 08:36: Horizon 2 Feb 2008 @ 20:35: nobody Knows 9 Jan 2008 @ 08:33: About the Day 5 Dec 2007 @ 17:25: Le Bateau Lavoir 21 Jul 2007 @ 22:00: Inspiration 18 Feb 2007 @ 22:16: On the corner 6 Dec 2006 @ 03:22: Antarctic Home 3 Dec 2006 @ 20:41: Our Resources 30 Nov 2006 @ 04:35: Long Dark Night
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24 May 2005 @ 07:56, by John Ashbaugh