Clathrate gun hypothesis - Wikipedia

Clathrates are a class of compound that consist of a cage of molecules that can trap gases, such as methane, in a solid form. For methane, the most important "cage" is one that is made of water molecules, and so is described sometimes as a hydrate. Some key facts about clathrates make them particularly interesting to climatologists. First, they may make up a significant portion of total fossil carbon reserves, including coal and oil. Current best guesses suggest that maybe 500 to 2000 gigatonnes of carbon may be stored as methane clathrates (5-20% of total estimated reserves). Some estimates are as high as 10,000 gigatonnes. They occur mainly on the continental shelf where the water is relatively cold, there is sufficient pressure and enough organic material to keep the methane-producing bacteria happy. Most importantly, clathrates can be explosively unstable if the temperature increases or the pressure decreases — which can happen as a function of climate change, tectonic uplift or undersea landslides.

Methane and the clathrate gun hypothesis of fast …

Methane and the clathrate gun hypothesis of fast climate change

Clathrate gun hypothesis (global warming) - mmo …

Enormous amounts of CH4 are sitting on the ocean floor in the form of methane hydrates (also called clathrates). Clathrates are cages formed by water molecules where gas molecules are trapped in the hollow space inside the cage. This symbiotic structure is stable at low temperature/ high pressure. The clathrate gun hypothesis speculates that a spontaneous release of methane from clathrates increases the atmospheric methane composition to the degree where the boosted greenhouse effect triggers climate change.

So far we have not found any sign of such catastrophic events occurring. However, it is speculated that less dramatic release from clathrates might happen during times of rapid climate change. Such events are hard to catch due to the short lifetime of CH4 in the atmosphere. Atmospheric CH4 originating from clathrates has a distinct isotopic composition of hydrogen. So far we are able to measure the carbon isotopic composition.

The master thesis project involves extending our measurement capacities to isotopes of hydrogen, testing the new system, and performing first measurements over a climatologically interesting time period.

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Over recent decades the growth rate of methane has oscillated significantly and, indeed, has been basically zero (i.e., no increases) for the last three years. The combination of changes in wetland emissions and climate-related cooling during the Mt. Pinatubo eruption (1991-1993) combined with changes in economic activity, particularly in the former Soviet Union, seem to explain most of this variability although there are still large error bars in these estimates. There is, however, one additional reservoir of methane about which very little is known: the methane clathrate reservoir in the oceans — the 600-pound gorilla of methane variability!

Dessus, B., and Laponche B., Herve le Treut, 2008. Global Warming: The Significance of Methane bd-bl-hlt January 2008.
Methane and the clathr...

Methane Clathrate Gun | Collapse of Industrial Civilization

The maximum mean global atmospheric temperature above which all the world’s icecaps will have completely melted away is estimated to lie between 7 oC and 8 oC above the mean global temperature which here is taken as 14.49 oC in 1990 (IPCC, 2007). The critical temperatures above which the Earth will entirely lose its ice caps are between 21.49 oC and 22.49 oC. It has been found however that the latent heat of ice melting curve first intersects the maximum lifetime stability line for atmospheric methane calculated from the methane global warming potentials (see. Figure 3) at the 20.964 oC extinction line (6.474 degrees centigrade above the atmospheric mean temperature of 14.49 oC in 1980) at 2050.1 and the 22.49 oCextinction line (8 oC above the atmospheric mean temperature of 14.49 oC in 1980) at 2051.3. Therefore the limits of the final melting and loss of all ice on Earth have been fixed between the 6.474 oC and 8 oC anomalies above the 1990 mean atmospheric temperature of 14.49 oC. This very narrow temperature range includes all the mathematically and visually determined extinction times and their means for the northern and southern hemispheres which were calculated quite separately (Figure 7; Table 1).

19/03/2013 · Methane Hydrates in Quaternary Climate Change: The Clathrate Gun ..

and hence much smaller than for the clathrate gun hypothesis

Because of the high methane global warming potential (1000) of the 2011, 20 oC temperature anomalies in the Gakkel Ridge region, the entire methane global warming potential range from 5 to 1000 has been used to construct the radiating set of temperature trends shown in Figure 3. The 50, 100, 500 and 1000 methane global warming potential (GWP) trends are red and in bold. The choice of a high temperature methane peak with a global warming potential near 1000 is in fact very conservative because the 16 oC increase is assumed to occur over a year. The observed ESRL-NOAA Arctic temperature anomalies varied from 4 to 20 degrees over less than a month in 2011 (Sam Carana, pers. comm. 2012).

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Climate Change: Clathrate gun hypothesis

With a plausible role for methane clathrates in the Paleocene, it is only natural to examine whether they played a similar role in more recent climate changes, such as rapid climate variability during the last ice age. There are some tantalizing clues. In ocean sediments offshore of California, Kai-Uwe Hinrichs and colleagues at Woods Hole recently found geochemical traces of clathrate releases coincident with warmings in the Greenland ice core records. In some records, there are coincident spikes in the carbon isotope record, reminiscent of the Paleocene/Eocene spike but of lower amplitude. This has led Jim Kennett to propose the so-called "clathrate gun hypothesis", that methane builds up in clathrates during cold periods, and as a warming starts it is explosively released, leading to enhanced further rapid climate warming. This idea is not yet widely accepted, mainly because the records of methane in the ice cores seems to lag the temperature changes, and the magnitudes involved do not appear large enough to significantly perturb the radiative balance of the planet. The more conventional explanation is that as the climate warms there is increased rain in the tropics and thus increased emissions from tropical wetlands which need to have been large enough to counteract a probable increase in the methane sink. There is, however, much that we don't understand about the methane cycle during the ice ages, and maybe hydrates will eventually be considered part of the rapid climate change story.