I think the problems from over population will eclipse anything global warming may or may not bring. By 2030 the world population is estimated to rise to 9 Billion. Added to that ever dwindling resources will lead to conflicts. The current population is around 6 billion with scientists already saying the world can only support 2 Billion comfortably (pre-industrial revolution levels) in the long term.
BBC NEWS | UK | Global crisis 'to strike by 2030'