Well, yes. You would have to have a tremendous amount of knowledge, which I don't believe anybody has, as to what the level of the emission would be, or else you would be running afoul of international trade agreements, probably article 20 of the WTO.
You would have to be very tight on the levy that you were applying at the border. I don't believe anybody has that information, so it would be very, very tricky to do that and not be challenged.