This New York Times article says we're totally screwed unless we develop new sources of energy that don't emit carbon dioxide. It suggests possible alternate ways of obtaining fuel, one of which is a space satellite that collects solar energy and beams it down as microwaves. But

The futuristic techology might be impractically expensive. Developing a solar power satellite, for example, has been estimated at more than $200 billion.

Er, here's the cost of the war in Iraq.

$83 billion so far. The next installment is $87 billion. That's $170 billion right there. I guess it all depends on what the definition of "impractically expensive" is.