We know orders of magnitude more about the global climate system and climate history than we did in 1950. We do know that there are potential alternative states and probably tipping points. But we don’t know what those alternative states are; nor do we know where the tipping points lie. Unless we know those things in convincing detail and with near-unanimity, the collective-action problems will bedevil effective action. And even if we did know such things in convincing detail, most of the collective-action problems surrounding carbon emissions would remain.

For these reasons I find Machiavelli’s wisdom appropriate to the human condition early in the 21st century. In The Prince (1513), he compared affairs of state to medicine: In both, events proceed with their own momentum, so that at the stage when problems are easy to resolve they are still very hard to detect, and by the time they are easy to detect they are exceedingly hard to solve.