The US suggests ruinous alternative energy sources!

Hey everyone! I think you have heard a hundred times already that Washington is calling the rest of the world to cut greenhouse gas emissions in order to avoid global warming that is allegedly originating mainly from such human activities as oil and gas refining. Instead of dearer petrol, the US suggests using biofuel that is said to be much cleaner and friendly to the environments.
Well, is it so indeed? Perhaps not. Nowadays more and more scientists and environmentalists begin to agree that the negative effect of using more biofuel greatly surpasses all possible advantages. This is first of all greater deforestation which is required to grow more oil seed rape, and using more chemical fertilizers which leads to soil salination and river contamination, as well as freshwater disposal overrun for irrigation.
Secondly, there is threat of starvation as less food is produced, which will enevitably cause a price hike for all food commodities.
So why does the US enforces using more alternative energy sources especially biofuel? So far as oil cost is increasing steadily, Washington does not want oil and gas suppliers to become strong enough and become able to stand against Amerira itself.