Everyone’s jumping on the environmentalist bandwagon these days, and they all want to steer.

Harvard economist Edward Glaeser, writing in the Boston Globe, says “Smart environmentalism has three key elements. First, policies should be targeted toward the biggest environmental threat: global warming. Second, our resources and political capital are limited. This means we must weigh the benefits of each intervention against its costs. Third, we must anticipate unintended consequences, where being green in one place leads to decidedly non green outcomes someplace else.”

I love the way economists think. If every policy wonk were legally required to reflect on trade-offs and unintended consequences, the world would be a better (and quieter) place. But when you’re good with a hammer, everything looks like a nail. Glaeser adds, “The most effective way to reduce emissions [of greenhouse gases] is to charge people for the social costs of their actions with a carbon tax.”

Unfortunately he stops there. Like today’s generation of best-selling atheists, who repeat David Hume and Bertrand Russell without noticing that their arguments persuaded few, Glaeser repeats the standard economic prescription without acknowledging its political difficulty. Everyone hates traffic congestion too, and it’s been well known for years that the way to cure traffic congestion is to tax it by charging time-of-day tolls, but it never gets done.

What’s the second-best strategy when you know perfectly well that the best one’s a nonstarter? Remember, Ed, you’re an environmentalist now, so shrugging your shoulders and going off to teach your next class is not an option.

(Good discussion on some points at Mark Thoma’s Economist’s View. And George Monbiot’s new book Heat popularizes and refines a potentially nifty idea for a carbon-rationing system. I don’t know if Monbiot’s right, but the last writer I read who made it seem so easy to combine deftness, personality, and sheer intellectual energy was named George Orwell.)