Climatewatch: positive feedback cycles II

Another surprising side effect of global warming (and positive feedback cycle to accelerate it) is the thawing of the methane-rich permafrost in Siberia:
Thawing Siberian permafrost
Warming hits 'tipping point'
It will take time, but it has begun already, and it can potentially contribute a 10-25% in global warming.
The effects on human habitat or its economic implications are another story.

If however, you do wish to see a possible timeline collage for this century, instead of borrowing a horror flick from your video store tonight visit The Frightening Future of Earth.