Climate Ethics has a thoughtful post up about climate change, scientific uncertainty, and ethics. While not particularly novel, the arguments are well and concisely expressed. Key among them is the basic ethical point Henry Shue has made about revolvers and the heads of others: even if you only have one bullet chambered, pulling the trigger is still an immoral act. It is the possibility of severe harm, rather than the probability of the harmful outcome, that is most ethically relevant.
The uncertainties of climate change are primarily about how bad it will get how quickly, as well as how quickly we need to act to stop it. There is also very strong consensus that the climate can change in ways that would be disastrous for humanity and that present activities materially contribute to the risk of that taking place.
On ethical grounds, it does not seem as though there are any remaining arguments for total inaction in the face of climate change. The question now is the degree to which our moral obligations to future generations compel us to make massive and rapid changes in our lives.