There are other indirect methods, such as oxygen isotopes. Can extrapolate the Milankovitch cycles backwards, too, and build global climate models based on landmass distribution. :grad:
While that's true, there's no proof that what the article describes actually happened. I found this on the Wiki regarding the Permian extinction event, which is what the article refers to.
However, only one sufficiently powerful cause has been proposed for the global 10 ‰ reduction in the 13C/12C ratio: the release of methane from methane clathrates;[7] and carbon-cycle models confirm that it would have been sufficient to produce the observed reduction.[95][98] Methane clathrates, also known as methane hydrates, consist of methane molecules trapped in cages of water molecules. The methane is produced by methanogens (microscopic single-celled organisms) and has a 13C/12C ratio about 60 ‰ below normal (δ13C -60 ‰). At the right combination of pressure and temperature it gets trapped in clathrates fairly close to the surface of permafrost and in much larger quantities at continental margins (continental shelves and the deeper seabed close to them). Oceanic methane hydrates are usually found buried in sediments where the seawater is at least 300 meters (984 ft) deep. They can be found up to about 2,000 meters (6,562 ft) below the sea floor, but usually only about 1,100 meters (3,609 ft) below the sea floor.[99]
The area covered by lava from the Siberian Traps eruptions is about twice as large as was originally thought, and most of the additional area was shallow sea at the time. It is very likely that the seabed contained methane hydrate deposits and that the lava caused the deposits to dissociate, releasing vast quantities of methane.[100]
One would expect a vast release of methane to cause significant global warming, since methane is a very powerful greenhouse gas. A "methane burp" could have released 10,000 billion tons of carbon dioxide equivalent - twice as much as in all the fossil fuels on Earth.[36] There is strong evidence that global temperatures increased by about 6 °C (10.8 °F) near the equator and therefore by more at higher latitudes: a sharp decrease in oxygen isotope ratios (18O/16O);[101] the extinction of Glossopteris flora (Glossopteris and plants which grew in the same areas), which needed a cold climate, and its replacement by floras typical of lower paleolatitudes.[10][102]
However, the pattern of isotope shifts expected to result from a massive release of methane do not match the patterns seen throughout the early Triassic. Not only would a methane cause require the release of five times as much methane as postulated for the PETM,[11] but it would also have to be re-buried at an unrealistically high rate to account for the rapid increases in the 13C/12C ratio (episodes of high positive δ13C) throughout the early Triassic, before being released again several times.[11]
He doesn't even have his geology right. There's no underground bubble of Methane waiting to explode, it's stored on the ocean floor trapped by temperature and pressure into a formation called a clathrate:
http://en.wikipedia.org/wiki/Methane_clathrate
The methane will only get released by a sudden rise in temperature in the levels where these are deposited, which is not going to be an issue with the BP problem.
» Fri Mar 19, 2010 5:26 pm 
