The tenth and final sustainability myth from Lemonick is:

Myth 10: Once you understand the concept, living sustainably is a breeze to figure out.
All too often, a choice that seems sustainable turns out on closer examination to be problematic. Probably the best current example is the rush to produce ethanol for fuel from corn. Corn is a renewable resource—you can harvest it and grow more, roughly indefinitely. So replacing gasoline with corn ethanol seems like a great idea. Until you do a thorough analysis, that is, and see how energy-intensive the cultivation and harvesting of corn and its conversion into ethanol really are.

One might get a bit more energy out of the ethanol than was sunk into making it, which could still make ethanol more sustainable than gasoline in principle, but that’s not the end of the problem. Diverting corn to make ethanol means less corn is left to feed livestock and people, which drives up the cost of food. That consequence leads to turning formerly fallow land—including, in some cases, rain forest in places such as Brazil—into farmland, which in turn releases lots of carbon dioxide into the atmosphere. Eventually, over many decades, the energy benefit from burning ethanol would make up for that forest loss. But by then, climate change would have progressed so far that it might not help.

You cannot really declare any practice “sustainable” until you have done a complete life-cycle analysis of its environmental costs. Even then, technology and public policy keep evolving, and that evolution can lead to unforeseen and unintended consequences. The admirable goal of living sustainably requires plenty of thought on an ongoing basis.

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