NPR's John Nielsen reports on the plan by several of the largest multi-national corporations to reduce the emission of greenhouse gases. The newly formed "Partnership for Climate Action," aims to identify gas emissions and voluntarily cut back on them. The plan is based on the idea of 'emissions trading systems,' which allow manufacturers to buy and sell the right to emit certain global warming gases. The plan will be monitored by the watchdog group, Environmental Defense. Other environmental groups are skeptical about such market-based methods of reducing pollution.