On Capitol Hill, the Senate has opened debate on a climate change bill supporters say would reduce fossil fuel dependence and cut emissions of carbon dioxide. The bipartisan measure aims to combat global warming by using a cap-and-trade system popularly known as carbon trading. This involves setting greenhouse gas emissions limits and allowances for each industry and then creating a system to trade the allowances. The White House opposes the measure as part of its objection to environmental regulation. But environmentalists, meanwhile, have warned it may not go far enough. Critics say carbon trading allows big polluters to delay the reduction of their emissions.