Methane is one of the most potent greenhouse gases. In the atmosphere it has a warming effect more than 20 times that of carbon dioxide.
Methane escapes into the atmosphere in many ways — rubbish tips, coalmines and cow farts are well-known sources. But the biggest known concentration of the gas is stored in ice-like formations beneath the ocean floor.
The formations — often known as clathrates — remain stable only within certain temperatures. Scientists have long speculated that a warming of the oceans could destabilise the clathrates and release great amounts of the dangerous gas into the air.
Nobody knows for certain what changes would trigger the clathrates to break down in big amounts. However, their breakdown millions of years ago is thought to have triggered catastrophic global warming that led to the largest mass extinction of species in history. The end-Permian extinction event occurred more than 250 million years ago.
Fossil records suggest about 96% of all marine species and about 70% of land-based backboned animals perished.
If climate change warmed the oceans enough, huge amounts of methane could be released. If so, average temperatures would rise by 10° Celsius or higher — just as they did 250 million years ago.
Disturbingly, the August 17 New Scientist reported that scientists had found up to 250 methane gas plumes rising in shallow waters from the Arctic Ocean seabed. The find is unprecedented.
The methane may be rising from deep within the Earth's crust. However, the sheer amount of methane released means it's more likely the source is clathrates. The ocean in the area had warmed by about 1°C in the past three decades. Human-made global warming is occurring fastest at the poles, where most clathrates exist.
It's not known if this is an isolated event. Very few other parts of the Arctic have been surveyed to detect methane emissions.
The retreat of the Arctic ice cap is also releasing methane from another source. As normally frozen soils in Siberia and Canada thaw, trapped methane gas escapes in ever-greater quantities.
The methane time bomb is ticking. Left unchecked, climate change will make it go off. The evidence indicates this will happen sooner rather than later. The only way to defuse it in time is for governments to make rapid cuts to emissions.