There's a bill in Congress that would affix a pricetag to greenhouse gas emissions. Unlike litter, we don't currently charge for this, though it affects us all.
Such a charge would make alternative fuels more competitive, because they would, in effect, be given credit for little to no greenhouse gas emissions. This New York Times article has more details, including interesting details about "closet carbons."
Is this a good way to encourage the development of alternative sources of energy? If not, what would work better?