Chicago, Illinois - A group of major corporations, this week, launched the nation's first trading program to reduce releases of carbon dioxide and other "greenhouse gases" through trades of credits earned by firms that exceed emission-reduction goals.

According to the Washington Post, the creation of the CCX marks an expansion of market-based steps to cut U.S. emissions linked to global warming. Such voluntary strategies have become a sharp fault line between President Bush and Democratic congressional leaders and some key Republican lawmakers as well.

Britain and Denmark have trading programs for greenhouse gases. A mandatory U.S. trading program has contributed to large-scale reductions in sulfur dioxide, a source of acid-rain pollution, experts say.

Patterned after commodity exchanges, the Climate Exchange intends to create verifiable ways of measuring reductions of greenhouse-gas emissions. Some measures will be direct, such as changes to more efficient industrial processes. Others will involve indirect emissions "offsets" through increased plantings of forests or farm products that absorb carbon dioxide, or steps to control gas releases from landfills, said Richard L. Sandor, the exchange's chairman and chief executive.

Each exchange member agrees to reduce average greenhouse-gas levels from 1998 to 2001 by 4 percent over the next four years.

The Bush administration opposes mandatory reductions in carbon dioxide and other greenhouse gases. Instead, the president has called for more research on global warming and new economic incentives to encourage utilities and manufacturers to gradually reduce the growth of emissions.

Bush's refusal to sign the Kyoto Accords has angered clean-air advocates worldwide.

A proposal this month by Sens. Joseph I. Lieberman (D-Conn.) and John McCain (R-Ariz.) would require U.S. power plants and industries to set targets for limiting greenhouse emissions.

Yesterday, Senate Democrats Hillary Rodham Clinton (N.Y.) and Barbara Boxer (Calif.) and independent James M. Jeffords (Vt.) -- all key players in the clean-air debate -- said they were unwilling to compromise with the administration on new clean-air legislation unless it includes cuts in carbon dioxide.

"We have been very clear in the Environment and Public Works Committee that we want to pass legislation that takes us forward, not backwards," Clinton said during a news conference called to criticize Bush's environmental record.