Methane (CH4) is a greenhouse gas that remains in the atmosphere for approximately 9-15 years. Methane is over 20 times more effective in trapping heat in the atmosphere than carbon dioxide (CO2) over a 100-year period and is emitted from a variety of natural and human-influenced sources. Human-influenced sources include landfills, natural gas and petroleum systems, agricultural activities, coal mining, stationary and mobile combustion, wastewater treatment, and certain industrial process. (reference)
There are enormous quantities of naturally occurring greenhouse gasses trapped in ice-like structures in the cold northern mud and at the bottom of the seas. These ice structures, called clathrates, contain 3,000 times as much methane as is in the atmosphere. Now here's the scary part. A temperature increase of merely a few degrees would cause these gases to volatilize and 'burp' into the atmosphere, which would further raise temperatures, which would release yet more methane, heating the Earth and seas further, and so on. There are 400 gigatons of methane locked in the frozen arctic tundra, enough to start this chain reaction, and the kind of warming the Arctic Council predicts is sufficient to melt the clathrates and greenhouse gases into the atmosphere.(reference)
Once triggered, this cycle could result in runaway global warming worse than the most pessimistic scenario. Strong geologic evidence suggests something similar has happened at least twice before. The most recent of these catastrophes occurred about 55 million years ago in what geologists call the Paleocene-Eocene Thermal Maximum, when methane burps caused rapid warming and massive die-offs, disrupting the climate for more than 100,000 years.
The granddaddy of these catastrophes occurred 251 million years ago, at the end of the Permian period, when a series of methane burps came close to wiping out all life on Earth. More than 94% of the marine species present in the fossil record disappeared suddenly as oxygen levels plummeted and life teetered on the verge of extinction. Over the ensuing 500,000 years, a few species struggled to gain a foothold in the hostile environment. It took 20 million to 30 million years for even rudimentary coral reefs to re-establish themselves and for forests to grow again. In some areas, it took more than 100 million years for ecosystems to reach their former healthy diversity.
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