For a concise and clear statement of one why to avoid the catastrophic effects of green house gas warming see:

http://www.youtube.com/watch?v=ltyicIEdHZY

Dr. James Hansen is generally reguarded by the scientific community of the USA as the their leading scientist in the area of climate change.  His experience in this area goes back three decades to when the likelihood of rapid warming by the greenhouse gases was first recognized.  Please listen to the carefully selected words of this man. Dr. Hansen's advice concerning what we should do now is the best and most credible I have heard so far.