Mark Thoma has an excerpt of Partha Dasgupta's review of Bjorn Lomborg's new book today. It took me a while to get Dasgupta's point, so let me try and rephrase it in a slightly simpler manner, since it was pretty opaque to me on a first reading.
Lomborg's argument is the easy bit. Look at all the money that Plan A – implementing Kyoto – would cost, and look at what benefits we would get in return for that cost. Now, look at Lomborg's Plan B. It costs a fraction of the cost of implementing Kyoto, and the benefits are much higher. So if we want to maximize the planet's welfare, we should do things like build infrastructure to protect against floods and hurricanes, while keeping the amount of carbon in the atmosphere to a maximum of 560 parts per million. The cost is lower, and the benefits are higher.Hang on a second, says Dasgupta. The problem with Lomborg's argument is that he thinks he knows what the costs and benefits of a world with atmospheric carbon concentrations of 560 parts per million are. But he doesn't: nobody does. You can't just extrapolate from what we're seeing at current concentrations of 380 parts per million, because the climate is a non-linear system:
The transition to Lomborg's recommended concentration of 560 p.p.m. would involve crossing an unknown number of tipping points (or separatrices) in the global climate system. We have no data on the consequences if Earth were to cross those tipping points....More>