As the United Nations climate talks in Durban progress, they are becoming increasingly combative, offering a soft preview of the kind of political atmosphere destined to prevail in a world where agriculture in vulnerable regions of the planet begins to succumb to catastrophic drought and flooding. The United States and Canada have drawn intense criticism here during the first two days of the conference. Participants lamented Canada’s new status as a “laggard country” when that nation’s conservative government announced its plan to quit the Kyoto Protocol, which it called a thing of the past. And, to almost no one’s surprise,...