1. The existence of global warming. (He assigns a 95%+ confidence level to this.)
2. Human contribution to global warming. (He assigns 90% confidence to this, but is uncertain about how much of the effect is due to human activity, though he references David Friedman's point that this doesn't make much difference to whether or not we should do anything about it.)
3. Magnitude of the warming effect.
4. Net harms or benefits due to warming. (He observes that the latter is often ignored.)
5. Extent of decentralized response. (How much will be done in the form of individual activity, changes in land prices, etc. to reduce negative impacts?)
6. Marginal impact of collective abatement efforts. (If all nations cooperated, how much of the negative effects could be abated or mitigated?)
7. Marginal impact of unilateral abatement efforts. (What can the United States do on its own, or at least without the assistance of emerging economies not likely to cooperate, and how much effect could that have?)
To which he adds that there are many more questions about specific proposed responses, their marginal efficacy, and costs.
If you have further suggestions for his list, post comments at Agoraphilia.