Rob Stavins has a good, concise overview of the session and the outcome on the Belfer Center website. Not as negative as some other observers, he highlights the extraordinary procecess that resulted in the Copenhagen Accord:
It is virtually unprecedented in international negotiations for heads of government (or heads of state) to be directly engaged in, let alone lead, negotiations, but that is what transpired in Copenhagen. Although the outcome is less than many people had hoped for, and is less than some people may have expected when the Copenhagen conference commenced, it is surely better – much better – than what most people anticipated just three days earlier, when the talks were hopelessly deadlocked.
Overall, he sees Copenhagen as a constructive move forward:
The climate change policy process is best viewed as a marathon, not a sprint. The Copenhagen Accord – depending upon details yet to be worked out – could well turn out to be a sound foundation for a Portfolio of Domestic Commitments, which could be an effective bridge to a longer-term arrangement among the countries of the world. We may look back upon Copenhagen as an important moment – both because global leaders took the reins of the procedures and brought the negotiations to a fruitful conclusion, and because the foundation was laid for a broad-based coalition of the willing to address effectively the threat of global climate change. Only time will tell.
I am no expert on foreign affairs, but it seems unlikely to me that continuing with the U.N. negotiating process is going to be fruitful. It worked (up to a point) at Kyoto, because nothing was asked of the developing countries. Even than, the agreement wasn’t able to obtain U.S. agreement. If you think of the key players as Japan, the EU, the US, and the four BRIC countries; Kyoto was only able to get three of the seven to commit to any action.
My guess is that the last-minute negotiations at Copenhagen were a harbinger of the future, which will be driven by agreement between the key players — the Great Powers of the coming era.
P.S. Another interesting perspective on Copenhagen can be found here.