Short & sweet: Jim Manzi @ NRO on climate cost-benefit analysis.
While Krugman immediately (and correctly) says such a comparison would over-simplify the real decision logic, it does illustrate the crux of the problem for advocates of aggressive efforts to reduce emissions: (1) For at least the next century, the expected damages caused by global warming are nothing like the doomsday pictures presented in the popular media, but are rather a few percent of GDP, and (2) the economic costs imposed by aggressive programs designed to avoid these damages are expected to be far greater than the damages that they should expect to avoid for the next 100 years at least.
And to be a little parochial about it, from the perspective of a U.S. taxpayer, the net expected economic damages to the U.S. from global warming are expected to be materially zero through 2100, while the costs, as indicated in the Krugman article should be about 2 percent of GDP by 2050. As per the prior analysis, mitigation costs should be higher by 2100. That is, even under some very favorable assumptions, citizens of the United States are being asked to sacrifice several percent of total income (i.e., trillions of dollars of cumulative consumption) for no tangible expected benefit for the next 100 years.