ENERGY

General Motors Corp., Monsanto Co., and British Petroleum said they will take voluntary steps to reduce emissions of carbon dioxide, the leading so-called “greenhouse” gas that many scientists say may lead to a serious warming of the Earth. A GM spokesman noted that the auto maker remains opposed to the climate treaty reached in negotiations last December in Kyoto, Japan, which calls for the United States to reduce greenhouse emissions to below 1990 levels by 2008 to 2012.