Richard S.J. Tol, a top climate economist, is somewhat surprisingly endorsing the extension of the Kyoto Protocol (here). His argument makes some sense - as he notes, the Protocol itself does not expire in 2012, only its emissions reduction targets do that. Still, I think the Protocol is fatally hampered by its overly ambitious emissions trading system and offset mechanisms that really are nothing more than an elaborate system for transferring resources from rich countries to poor countries with no necessary impact on global emissions of greenhouse gases.
If some amount of mitigation is presently desirable (which I think it is, though others might reasonably disagree), then it would be far better to replace the Kyoto mitigation regime with something closer to the European Union's Emissions Trading Scheme, which limits the use of offsets and limits emissions trading to the most easily measured combinations of sources and greenhouse gases - namely carbon dioxide emissions from four major emitting industries.
I suspect, however, that the international community will do more or less what Tol suggests - extend and expand on the Kyoto Protocol - if (but only if) the US adopts, as expected, an emissions trading scheme that is closer to the Kyoto model than the EU model.