Senate debate this week on climate change is a step forward, even if it doesn't produce a law limiting carbon emissions.

A vote on such legislation was unthinkable as recently as two years ago. President Bush had set a hostile tone in Washington, denying that global warming existed and attacking the sound scientific research that had documented the problem.

Now, Bush concedes global warming is a reality. But he still isn't likely to sign the bill that the Senate is debating, believing that it could impose trillions of dollars in new costs on consumers and businesses.

The bill, sponsored by Sens. Barbara Boxer (D., Calif.), Joseph I. Lieberman (I., Conn.), and John W. Warner (R., Va.), would put a cap on carbon emissions, lowering the limits each year beginning in 2012. Permits could be bought and sold. Four years from now, industries that emit greenhouse gases - such as electric power plants, natural gas producers, and manufacturers - would need to purchase "allowances" to pollute.

Most of these allowances would be auctioned off, but about 40 percent would be given away to help certain industries ease into this new regulatory world. Money raised through the auctions, an estimated $3.3

trillion

by 2050, would provide tax cuts for low-income consumers to help pay their utility bills, and finance new energy research, among other uses.

Sen. Arlen Specter (R., Pa.) has sponsored an alternative approach that many environmentalists view as counterproductive. Specter's bill offers a compromise - a "safety valve" that would eliminate emissions caps for polluters if the cost of compliance reached a specified ceiling.

This option gets at the political problem by attracting votes from senators in states where the cost of industry compliance could be especially high. But it also would undermine the effectiveness of environmental controls. The Senate's purposefulness in attacking global warming would be strengthened if Specter instead joined forces with Boxer, Warner and Lieberman.

Carbon dioxide emissions are affecting agriculture, weather conditions, and our quality of life. The longer the United States hesitates to take a leadership role on global warming, the longer it will take to blunt the damaging effects of climate change.

Meaningful action might have to await a new president, but the Senate can provide a strong foundation for it now by passing the Boxer-Lieberman-Warner bill.