A new report from the Congressional Budget Office confirms one of the most depressing facts about climate change: The best policy is the one that’s going nowhere in Washington.

The CBO report concludes that a tax on carbon emissions “would be the most efficient incentive-based option for reducing emissions and could be relatively easy to implement. If it was coordinated among major emitting countries, it would help minimize the cost of achieving a global target for emissions by providing consistent incentives for reducing emissions around the world.” But the major presidential candidates aren’t supporting such a tax, and the few proposals on Capitol Hill to impose a tax are not expected to go anywhere anytime soon.