This is now no longer a potential threat, but a proven reality. As the Arctic warms, methane hydrates long frozen beneath the surface are beginning to melt. Is this the tipping point? Probably not. But it does indicate that the possibility is not science fiction scaremongering, but science fact. The BBC reports:
As temperatures rise, the sea-bed grows warmer and frozen water crystals in the sediment break down, allowing methane trapped inside them to escape.
The research team found that more than 250 plumes of methane bubbles are rising from the sea-bed off Norway.
Writing in Geophysical Research Letters, the team says the methane was rising from an area of sea-bed off West Spitsbergen, from depths between 150m and 400m.
So this new evidence shows that methane is stable at water depths greater than 400m off Spitsbergen.
However, data collected over 30 years shows it was then stable at water depths as shallow as 360m.
Methane bubbles observed by sonar, escape from sea-bed as temperatures rise
In our paper Getting There, we have come out in support of a 40% target by 2020, which still only gives us a 50/50 chance of keeping warming at or below 2 degrees, and atmospheric CO2 at 450 ppm.
What if this is simply not enough? The 350.org crowd very sensibly call for a return to 350 ppm, which is the CO2 range wherein humans have evolved and prospered.