As James Hansen in this video says "We DO have an emergency". He talks about climate tipping points such as the loss of summer Arctic sea ice amplifying the release of methane in permafrost on tundra landscapes and methane hydrates in the shallow East Siberian and Alaskan continental shelves. These tipping points have catastrophic consequences for our climate.
Climate tipping points are processes we don't want to launch. They are climate feedback mechanisms which take any sort of control over global warming out of our hands and threaten widespread species extinction and threaten the viability of civilisation and perhaps even human survival.
They could act either as slowly accelerating feedback mechanisms which keep increasing global temperatures by several degrees or a relatively sudden 'methane bomb' in which a large abrupt release of methane occurs. In either case, it would be disastrous for human civilisation, although in the first instance we would be like the frog in a pot of water being brought slowly to the boil, not having the where-with-all to notice the incremental changes before it is way too late.
Related: The United Nations Environment Program released a scientific report - Policy Implications of Warming Permafrost - at the Doha climate talks highlighting the threat from methane from melting permafrost. See Methane and CO2 in thawing Arctic permafrost a climate tipping point | Radio Ecoshock: Climate: Arctic Thermostat Blows Up , particularly the Interview with Paul Beckwith (MP3) from the Arctic Emergency Methane Group
