WASHINGTON -- Two top Senate Democrats are set to introduce a climate-change bill this week that would put new limits on carbon emissions, as world leaders prepare for a climate summit in Denmark after agreement last week by the G-20 nations on phasing out subsidies for fossil fuels.

Sens. Barbara Boxer, D-Calif., who chairs the Senate Environment and Public Works Committee, and John Kerry, D-Mass., will reportedly unveil their bill tomorrow after months of closed-door meetings.

The bill will be modeled largely on legislation passed by the House in June that aims to cut carbon emissions by 17 percent by 2020 and more than 80 percent by 2050, compared to 2005 levels, reported ClimateWire and other publications.

But it's unclear how far the bill will get this year, or how fast. The bill from Ms. Boxer and Mr. Kerry would come as senators are intensely busy with health care legislation, President Barack Obama's top domestic priority. Mr. Obama is aiming to sign a health care overhaul this year that would cut costs and cover the uninsured.

At the same time, the Boxer-Kerry bill also comes just over two months before a Dec. 7 meeting in Copenhagen, where world leaders are hoping to finalize a new agreement to reduce greenhouse gases. At last week's G-20 meeting in Pittsburgh, leaders pledged to "intensify [their] efforts, in cooperation with other parties, to reach agreement in Copenhagen." They also agreed to slash subsidies in the "medium term" for oil and other fossil fuels.

A climate-change bill faces a steep climb in the Senate after passing the House on a narrow 219-212 vote in June. Republicans have consistently portrayed Democrats' efforts to reduce global warming as a tax on families and businesses, and say it will lead to loss of jobs and U.S. competitiveness. Moreover, Democrats from industry-heavy states like Ohio and Michigan want breaks for manufacturing industries that would be affected by the legislation's caps on emissions.

Mr. Obama argues that the House bill will create jobs through new energy investments, but critics say the "cap and trade" system at the heart of the bill amounts to a tax. Under the "cap and trade" system, companies would buy and sell permits to meet emissions limits.

Washington correspondent Daniel Malloy writes the "Pittsburgh On The Potomac" blog exclusively at PG+, a members-only web site of the Pittsburgh Post-Gazette. Our introduction to PG+ gives you all the details.