It's been a Facebook meme. What if we create planet-friendly green energy, end pollution, create millions of jobs, and it turns out we didn't need to?
If you count only the possible benefits of a policy, you can make a great case for that policy.
The "worst that can happen" is that we spend trillions of dollars trying to solve a problem that we can't do anything to stop; that we misallocate scarce resources in a way that slows economic growth; that slower growth leads to less economic opportunity for Boston College grads and especially the world's poor, and that America and the world become much less wealthy and technologically advanced than we would otherwise. All of which would make the world less able to cope with the costs of climate change if Mr. Kerry is right.