San Francisco Chronicle: At last, Washington is engaged in a serious effort to curb global warming. In the House, Reps. Ed Markey, D-Mass., and Henry Waxman, D-Los Angeles, have put together legislation designed to reduce domestic greenhouse-gas emissions by 20 percent over the next decade. One of its key – and most controversial – strategies would be to establish a mandatory cap-and-trade system in which oil refineries, manufacturers and other major carbon emitters would buy and sell credits based on their …