And for how many years/decades/centuries/millenia has this gone on?
Since 2001, of course.... Bush's fault:
Just because it has not been seen does not mean it has not happened. I am sure we have all sorts of monitors and detectors now to tell us what is happening out there.
Methane venting suspected as cause of several past mass extinction events
http://thejacoblog.com/costa-rican-earthquake-releases-methane-bubbles/
We just watched the horrible SyFy movie “Ice Quake” last weekend, of course in this silly movie the methane earthquakes were blamed on global warming...
However, there is an element of scientific fact in the catastrophic potential effects of a massive methane release into the oceans or atmosphere (read up on theories of methane hydrate gasification as a cause or contributor to the Permian Triassic extinction (the Great Dying, Paleocene-Eocene Thermal Maximum) and other mass extinction events possibly triggered by climate change)
Relatively local gas venting events in Africa in the vicinity of certain volcanic lakes have wiped out entire villages and all surrounding life and may pose future threat to millions
http://www.guardian.co.uk/world/2009/jul/26/africa-lake-kivu-co2-gas
As the planet warms and sea levels rise, it is inundated with seawater, which is 12-15 degrees warmer than the average air temperature.
The areas of these methane ‘fountains’ is 150 ft UNDER WATER. Since man caused ‘global warming’ the ocean level has not risen even an inch, and in fact has been going down the last few years.
Anyone with a brain should realize that trying to blame man for what is going on on the sea floor 150 ft below the surface is a moron.