The Economist argues against a US carbon border tax:

[T]he costs of a border tax could be huge, not just because of the massive bureaucracy needed to certify the carbon content of different goods imported from different factories in different countries, but also because such a tax would be a dangerous weapon in the hands of America’s growing gang of protectionists.

The people who worry most about the costs of trying to constrain carbon emissions are the very ones demanding protectionist measures. But if those measures are passed, America risks something far costlier than a switch to cleaner energy: a global trade war.