Nonetheless, some of the most vocal supporters of a carbon tax are conservatives. One of Mitt Romney’s economic advisers, Harvard economist Greg Mankiw, is a huge fan of raising taxes on activities that are seen as undesirable—say, polluting the air—and cutting taxes on desirable activities, like working harder. So is supply-side economics guru Art Laffer. Former South Carolina Rep. Bob Inglis, a Republican, just started a whole think tank to push the approach.

“There is certainly progress in the way of thinking about emissions reductions that we haven’t heard from Republicans over the last three years,” said Mr. McDermott, who acknowledged that his bill is essentially a marker thrown down to influence debate in the next Congress.

Raising taxes on dirty energy and cutting taxes on capital could lower emissions, boost employment and boost the economy, researchers at Brookings Institution found recently.