Cap and trade is the tax that dare not speak its name, and Democrats are hoping in particular that no one notices who would pay for their climate ambitions. With President Obama depending on vast new carbon revenues in his budget and Congress promising a bill by May, perhaps Americans would like to know the deeply unequal ways that climate costs would be distributed across regions and income groups.

Politicians love cap and trade because they can claim to be taxing "polluters," not workers. Hardly. Once the government creates...