It's pretty well explained in Al Gore's An Inconvenient Truth, albeit being a little one sided. But the main point is, we have all the alternatives available, it's just that we are still under the grip of foreign oil that the companies don't care for us to become dependent from. As long as we guzzle gas, they keep their profits. But what they don't seem to realize is that they could gain more of a profit and monopolization from being the first to switch to alternatives. Or they do realize it, they just want to milk the cash cow for as long as possible. It's one of the reasons the US hasn't signed on the Kyoto accords.