1. I make no judgement about whether or not CO2 causes global warming. It may cause it, it may cause it but to a lesser (or greater) effect than sun cycles, cosmic radiation (and it's effect on cloud formation) or natural variation in the climate. I'm just asserting that my confidence in knowing one way or the other when you can't create control experiments is low. Ultimately proving causation instead of simple correlation is something that I believe is near impossible for something as large and complicated as the climate. Especially when the data being analysed for correlation relies hundreds of thousands of years of extrapolated proxy data (tree rings, ice cores, sediment, etc).
2. (this is tangential to the discussion of reproducibility in science) I think there is something lost to going to green energy - cost and power density. The unfortunate fact is that fossil fuels are incredibly cheap compared to green energy and they are more easily transportable. Carbon regimes threaten the ability of the third world to build itself out of poverty and threaten the global economy in general. I'm not saying we shouldn't invest in new forms of energy (especially wind and nuclear), in fact I think we certainly should. But I don't want to hamstring economic progress for some calamitous event with something I have low confidence will actually happen.