Senator McCain gave a speech in Portland, Oregon Monday reiterating and explaining his longstanding support for a “cap-and-trade” approach to global warming. He proposes that the government require reductions in greenhouse-gas emissions but allow companies to trade emissions credits, supposedly creating an efficient, market-based distribution of the regulatory burden. Support for this policy is the biggest mistake his campaign has made so far. Early in this speech, Sen. McCain ran through a litany of woes that we can expect from global warming: “reduced water supplies, more forest fires than in previous decades, changes in crop production, more heat waves afflicting...