1. How large are learning by doing effects for renewable energy technologies such as wind and solar?
2. How much damage will we suffer from climate change if average world temperature increases by T degrees? Where T takes on the values 1, 2, 5, 10, 30 c? Marty Weitzman's point is that each of these states of the world have non-zero probability of taking place. So, how much damage and who suffers the damage from each of extreme weather events?
3. When carbon pricing is introduced, which industries, nations and households will bear the incidence of this taxation?
4. Are consumers indifferent between "natural capital" and man-made engineered products? So for example, think of gentically modified foods versus organic foods -- are you indifferent? Is there any price differential such that you would be indifferent or do you view the GMO as "frankenfoods" that you wouldn't touch?
5. What are the causes of environmentalism? When people are environmentalists how does this affect their answer to #4 above?
6. Building on #5, we need structural consumer demand estimates of the willingness to pay for "green" products (think of the Prius) or tofu and how these estimates vary by population demographics and ideology.
I think these are great questions and topics for discussion and research. It is interesting to note how many of Matt's questions are empirical. "How large" in #1, "How much" in #2, "how does this affect" in #5, "how [do] these estimates vary..." in #6.
Others I can think of...
How will the incidence of increasing energy/carbon prices differ in the short-run vs. long-run?