Science blurb...Climate change yet again.

I had a conversation with my good friend Ross on Sunday about global warming. Ross embraces the precautionary principle. You can read about that in detail here, but briefly the idea behind it is that if there is even a slight possibility of a catastrophic event we ought to do everything possible to prevent it, as a precaution. I have several problems with this line of reasoning, but one of them was illustrated today when one of the scientists in the UN upon whom the Nobel committee bestowed their prize declined to accept it because he says the evidence to support global warming is insufficient and in fact contrary to the propaganda. It seems to me that there has to be some agreement that the event is a significant probability. Why not use all our planetary resources to build an asteroid shield or a defense against alien invasion? Those would have equally or even greater catastrophic consequences on the earth, yet, people don't advocate this. That is because we have not come to agreement that the probabilty of the event warrents the risk. So it is with global warming.