Just to get back to OP, climate change etc.
I'm not saying climate scientists are perfect, and I recognize that their importance in society, and their chance of getting funds, rises if they claim the climate changes due to man's actions.
The point is that the scientific community at that point needs to take action and do meta studies, assign some research groups to the subject that have never dealt with it before to see what they think of it, etc.. The problem is scientific, not religious, and I'll attack any of the sides, pro and con, scientists, politicians and businessmen alike, if they reduce this very important subject to a question of "I do/don't believe this happens."
As for carbon credits,
Let's assume for a second that man-made climate change is a proven fact. Then they're very useful. They introduce a financial penalty to products that pollute a lot, giving consumers incentives to buy eco-friendly products (note, we're still working under the assumption the scientists are right, whether you agree with them or not) and manufacturers incentives to make their manufacturing processes as green as possible. I believe that once you arrived at the conclusion that there's such a thing as anthropogenic climate change, the introduction of some form of correcting system such as carbon credits becomes inevitable.