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Originally Posted by Quazar
...there is more importantly the issue of renewable fresh water, which depending on whose projections you follow, has just a short a life span as fossil fuels.
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Err... Ever hear of rain? The fresh water problems exist fin places like the southwest where they build cities that far exceed the available water supply, or the Great Plains, where they mine aquifers to grow irrigated crops (evolved to grow in far wetter climates) instead of things suited to the local environment. But visit places like Voyageurs National Park or the Boundary Waters Canoe Area, and you will see that lack of fresh water is hardly a problem. Then there are those Mississippi floods...
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Any fuel, like ethanol, that is based on fresh water requirements is not a viable alternative to fossil fuels and should not be looked at as a future source of energy.
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Whyever not? The problem is not lack of fresh water, it's trying to grow stuff that needs lots of water in places where there isn't that much. Likewise for the CO2 issues &c. Sure, by doing the growing & processing in a deliberately inefficient manner, you might be able to create some example that uses more energy or creates more CO2 in the production process that is captured, but those aren't the norm.
You do need to remember that in the long term there simply isn't an alternative.