Well, guilt motivates some people, I suppose. But not many. And guilt trips are especially counterproductive when people feel like they don't have any reasonable low-guilt options. Rather than clamoring for better options, many people just give up, and come to think of "guilty behavior" as inevitable, perhaps even desirable -- and, paradoxically, the result of personal choice, rather than a system that constrains choice.

This brings up a more general worry of mine: that "green consumerism" -- broadly speaking, the idea that responsible lifestyle choices can create a more sustainable world -- misses the point.

Options that are simultaneously reasonably mainstream, reasonably affordable, and environmentally virutuous are rare. I'd like to buy a hybrid car, for example, but the Prius comes loaded with more extras than I'd like to pay for, so it's uneconomical for my family's driving habits.

In the same vein, lots of people would like to live closer to their jobs, in neighborhoods with great transit service or where stores and services are a short drive away. But housing in those sorts of neighborhoods is pricey, since there's a lot of demand and not much supply -- in part because of subtle disincentives to compact development that are embedded in tax and zoning codes. So many people are forced to settle for less expensive housing in car-oriented neighborhoods.

So there are two instances -- cars and houses, which together are responsible for an enormous share of our personal environmental impact -- where the range of reasonable choices is cosntrained by forces that are largely outside any individual's control. Even people who do respond to guilt trips -- people who'd opt for the greenest lifestyle that's within reasonable reach -- don't have a lot of good choices available to them.

I'm not saying that promoting green lifestyle choices is a waste of time. Far from it. But far, far more important is giving people -- not just green consumers, but everyone -- a wider range of environmentally friendly choices, and the incentives to make the right choices.

As Professor Robinson points out, we have a lot to learn from the field of public health in this regard. Lecturing smokers on the dangers of smoking only did so much. But systemic changes -- higher cigarette taxes, new medical treatments, and the like -- were far more effective. Where guilt failed, guilt-free incentives helped do the trick.