COP-15 ended over 3 weeks ago. The immediate outcome disappointed many optimistic observers, but the longer term outcome is still unclear (yes, I know what Keynes said). Personally, I expected nothing more. In essence, I think the outcome shows that none of the major emitters, like Shakespeare's Hamlet, consider suicide as a plausible option. In other words, the real issue not whether climate change is a real threat, the conflicts are about cost-effectiveness and justice. The most important lesson from the conference is that the UNFCCC may not be the right venue for an initial agreement among major GHG emitters.
There's been a lot of harsh criticism about the outcome of the conference, but considering the fact that UNFCCC's decisions require unanimity among its near 200 members; the "noted" Copenhagen Accord is probably as good as it gets. As Robert Stavins has pointed out, it would make much more political sense to initially forge a strict agreement among 20 largest polluters who account for 90 % of all emissions (i.e. a venue such as the Major Economies Forum on Energy and Climate or the G-20). That should be the first step, and it is challenging on its own. Only once that is achieved can the UNFCCC play a meaningful role.
In my opinion, the most realistic analysis on the outcome of COP-15 was offered by Robert Stavins, David Doniger, and WRI's Rob Bradley. Among others, CU Earth institute's Jeff Sachs, not surprisingly, hoped for much more.
On another but somewhat related topic, Ian Parry's recent paper on optimal taxes on highway fuels gives more evidence why corrective Pigouvian taxes make sense (I briefly commented on this topic last June). Not that the logic requires any more proof. It also applies to all other anthropogenic GHG sources.