In 1968 Toronto economist John Dales proposed that governments decide how much pollution to allow, print exactly that many rights, and sell them. The episode lays out the competing answers of Pigou, Coase, Crocker, and Dales, and corrects the origin story: the first real trading program was the 1982-87 lead phasedown, not acid rain. Carbon is harder, since a market must count tonnes that are invisible, avoided, or stored in trees.
Crocker and Dales are credited as independent originators of tradeable permits. The phrase "first trading program" is contested, since earlier EPA offsets and bubbles existed, and the lead program's roughly 20 percent savings is an EPA estimate.