Supporters argue that the shift away from fossil fuels can be made without significant economic damage and that failure to address global warming itself would produce greater economic harm later this century.
Bush, during a White House event that focused on keeping taxes low, said the Senate bill "would impose roughly $6 trillion in new costs on the American economy." The president in the past has expressed opposition to mandatory limits on carbon dioxide and other pollution linked to global warming.
"There's a much better way to address the environment than imposing these costs ... which will ultimately have to be borne by American consumers," said Bush, who has favored voluntary efforts and technology innovation to address global warming.
Bush did not say how the $6 trillion figure he cited was arrived at.
No one is sure what greenhouse emission reductions would cost the U.S. economy. Computer model-based studies have provided a wide range, from a modest rollback in annual economic growth to an annual economic loss of as much as $4.6 trillion by 2030. The wide range is based on different assumptions as to the success of shifting away from fossil fuels toward alternatives and increased energy efficiency and conservation.
The Senate bill assumes getting $6.7 trillion over the next four decades from the sale and trading of carbon emissions allowances in order to meet the imposed emissions caps. Under the bill, the money would be used to help industries comply with the carbon reductions and to help people pay for higher energy costs.
Sen. Barbara Boxer, D-Calif., a chief sponsor of the legislation, said the bill, as a result of the proceeds from emission allowances, "will give us the resources to help consumers with energy costs, without increasing the (federal) deficit." About $800 billion over 40 years would be earmarked for tax breaks to help people pay energy costs.
Meanwhile, environmentalists maintain that the debate should include the cost of not addressing climate change.
"These costs (of doing nothing) dwarf the kind of costs that people are talking about from taking serious initiatives to do something about climate change," said Frank Ackerman, a Tufts University economist and co-author of a recent report on the potential economic impacts of global warming. He predicted huge annual economic costs by the end of this century from climate change, including water shortages in the West, sea level rise, increasingly intense hurricanes, and higher energy costs.
While the Senate is expected to debate the climate legislation extensively and consider a string of amendments -- some weakening and others strengthening the bill -- the legislation's chances of passing the Senate are viewed as slim. Supporters are not expected to muster the 60 votes needed to overcome a filibuster threat, likely leaving the issue for next year and a new president.
The bill would require an 18 percent reduction of greenhouse gases below 2005 levels by 2020 and about 70 percent below that level by 2050. Some sources would not be covered, so the overall U.S. emission reductions would be by about two-thirds by 2050.
The bill recently picked up support from a dozen unions, the nation's mayors, a number of governors and religious groups. General Electric Co., Alcoa Inc., and Exelon Corp, the country's biggest operator of nuclear power plants, are expected Monday at a news conference with Boxer and Sen. Joe Lieberman, I-Conn., another chief sponsor, to support the legislation.
But many business groups, including the U.S. Chamber of Commerce, have criticized the measure as too costly. The charge against the bill has been lead by those that would be most affected including the oil and coal industries.