That would help green energy.  But the government won't do that, at least not in the US.  There would be a huge public outcry if they tried.  Plus, the government is in bed with the oil companies, so there's no way they will anyway.

Edit: It is noteworthy that while I don't think the US government would raise the cost of non-green energy, they do have a lot of incentives that promote green energy, like grants for research, tax breaks for building and installing green energy infrastructure (like adding solar panels to a home), etc.