My friend Bjorn Lomborg has a new book out that I haven't had time to read. But Partha Dasgupta has and his critique seems valid to me. Money quote:

If there is one truth about Earth we all should know, it's that the system is driven by interlocking, nonlinear processes running at different speeds. 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. They could be good, or they could be disastrous. Even if we did have data, they would probably be of little value because nature's processes are irreversible.

Megan calls these issues "catastrophic unknowns". They apply to the climate and to Iraq. My conservatism makes me fear the worst - and makes me want to insure myself against it.

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