The fundamental drive of Eaarth is that we're going to have to do more with less, and that externalities are disguising the true cost of lots of things. You probably know him primarily as the hippie who uses charts and tables to demonstrate that nuclear power isn't cost-effective once you get rid of the externalities and that actualized costs of nuclear power are always far greater than theoretical costs.

As far as food, he uses an example of a local butcher he tries to get involved in making local bacon - which they beg off of, because they can't make bacon for less than $14/lb. The fundamental point McKibben makes is that $14/lb bacon is okay because it's something we can eat indefinitely, while $3/lb factory-farmed bacon is not because of the externalities. His take on power generation is similar: if you can't do sustainable power for 45 cents/kWh, you need to use less power.

Perhaps most importantly, his basic stance is that these are not choices we get to make. These are choices being made for us and we can choose to plan for them or we can get smacked upside the head by them.