I just read The Chapter Five (in this book) and I’ll go as far as to say the critics don’t even have a point.
The chapter motivates geo-engineering without saying anything outlandish about the science (as far as this semi-informed lay-person can tell). There’s not even as much as an implication in the whole chapter that global warming isn’t a big deal. In fact, such a level-headed discussion of solutions to the problem actually bumped up my subjective probability of global warming being an issue to worry about. There’s no use fretting over something we can’t, practically, do anything about. It appears more likely to me, now, that we can do something about global warming.
The authors haven’t given up on marginal analysis, they seem to get that people respond to incentives and they appear to be aware of Pigovian-type taxes. They explicitly address the problems with carbon pricing and move the discussion forward with their description of one alternative policy (i.e. subsidized research in bio-engineering).
The reaction to this chapter was just plain strange.