An economist who devised the “cap and trade” system for regulating pollution is now voicing doubts about its ability to seriously address global warming. The climate bill passed by the House in June includes a cap-and-trade provision allowing firms to trade emissions permits. The system has been criticized for creating new incentives to pollute through a market for carbon “offsets” that don’t necessarily make up for the damage of the initial emissions. In an interview with the Wall Street Journal, the economist who came up with cap-and-trade in the 1960s, Thomas Crocker, said, “I’m skeptical that cap-and-trade is the most effective way to go about regulating carbon.” Crocker said he favors imposing a firm tax on emissions that would be easier to enforce.