a simple economic test of whether a "green" choice is really green
When trying to figure out whether some allegedly green technology alternative is actually green, the easiest way to get a first answer is to ask yourself, if oil were $700 a barrel and gas were $25 a gallon, would this idea still work? If it's really green, like a windmill or a community garden, it'll work better than ever; if it's fake-green, it'll fail.
(Of course, there can be side issues that are not fully addressed. For instance, by this test plutonium is quite green. But for most things this is a good first test.)
Some things fail this test as currently implemented, but with adaptations could pass it. For instance, corn ethanol. At present our corn is totally fossil-fuel dependent, and our ethanol doesn't yield much carbon savings. But other ways of making ethanol from crops could do very well in a world where oil is genuinely expensive. Some of those ways are being used now in poorer countries.
Our public policy challenge is essentially to create incentives for people to make fossil fuel decisions as if it were already expensive.