I will diverge from the discussion inorder to explain something important:
If I would see cutting evidence that the earth is infact warming, I would think we should do everything to save it. But there is no such evidence. Earth warming has to do with natural weather cycles as much as with human actions. Once Europe was covered with Ice, Once the Saharah had water, once the hudson was frozen. Weather change over the centuries, this is something that we must take into accout. Earth had warmer weather many times in the past. The thing that we must worry about is the human future - but if our Earth is warming from natural causes - starting to bike isn't gonna help. Europes ice melted when the cave people didn't have cars.