I mention this because this is one reason it is very hard to say what effect the push for biofuels will have on the prices of other crops and on overall welfare. If there is increasing demand and thus price of corn, what will happen to the price of other crops in the short and long term? Well it depends on what is being planted and where, the magnitude of the cross-price elasticity of demand for other crops - even how new fuels will effect transportation costs. As you can see, blaming biofuels for rapid commodities price escalation (or defending them) is dangerous business. It is also true, however, that general equilibrium effects are often not thought about very much in casual discussions of environmental economics.
For example, I wonder what the effect would be if there was mass consumption of Priuses (Pri'i?). On the one hand this would reduce gas consumption dramatically, but it would also put pressure on the production of all the junk that goes into the batteries. How much energy does it take to get the stuff? How much pollution does this create? What about waste? I don't know the answers to these questions, but many good ideas, when considered in mass amounts, often become questionable.
This, apparently, is true of biodiesel. Now that many people have converted to biodiesel the supply of used cooking oil is not keeping up with demand (despite my appetite for fish and chips). So now what? - the economic rationale has changed, does biodiesel still make sense? I don't know. But I do get grumpy when good ideas in isolation are not thought about in a general context - in the general equilibrium.
One final example. My wife and my mother were talking very admiringly about the freecycle movement and the idea that one could help the world by not buying new stuff. Hmmm... OK, so I am an economist and not helping my rep by taking this on - but I see a few problems with this. First, there is a market for this stuff, from people who can't afford new. If middle class people started gobbling this stuff up, that would just either increase the demand for Wal-Mart style cheap stuff from China of further impoverish people who are already impoverished by driving the price of used stuff up beyond their means. To put it plainly, you are not decreasing the demand for the stuff, just shifting who buys old and who buys new. Also, why s consumption of new stuff such a bad thing? This adds income and thus growth to the world. If you care about poverty, this should be reason for pause.
This did not go over well with the wife and mother.
My apologies for the slow blogging - life has been a bit crazy.