A Senate committee approved landmark legislation in December that would for the first time set mandatory U.S. limits on emissions of greenhouse gases.

The bill calls for the United States to cut carbon dioxide and other greenhouse gas emissions 70 percent by 2050 from electric power plants, manufacturing and transportation.

The bill was approved 11-8 by the Senate Environment and Public Works Committee. GOP critics of the bill arguing that limiting greenhouse gas emissions could become a hardship because of higher energy costs, promised a fight on the Senate floor.

But Sen. John Warner of Virginia, a Republican co-sponsor who gave the bill legitimacy among many moderate GOP senators, called it "a chance to give America our opportunity...to be counted on this very, very important issue."

"We now move to the Senate floor," said Sen. Joe Lieberman, I-CN, who along with Warner had introduced the legislation.

In September, Maryland Gov. Martin O'Malley and Virginia Gov. Tim Kaine, along with scientists from the region, had testified before the committee that the United States needed strong, mandatory federal action to control greenhouse gases, warning that climate change posed a major threat to the Chesapeake Bay.

"We don't want to see the work that we're starting to do in earnest be jeopardized by what we are seeing in the area of climate change," Kaine told the committee.

Numerous recent reports warn that climate change will raise sea levels in the Bay, drowning tidal wetlands, eroding islands and increasing flooding. A growing frequency of severe storms, which flush more nutrients into the Bay, along with warmer temperatures, which reduce the oxygen content of water, would make cleanup efforts more difficult.

Warmer temperatures could also harm many species, including striped bass and blue crabs, and even erase eelgrass-which provides underwater grass habitat in the lower Bay-from the Chesapeake.

The bill would create a "cap-and-trade" system whereby companies would have pollution allowances that they could sell if they went below the emission limits, or buy if they found they could not meet the requirements.

The trading is aimed at reducing the economic impact of putting limits on carbon dioxide from burning fossil fuels, the leading greenhouse gas.

The bill has many intermediate goals that come due before 2050, such as reducing greenhouse gas emissions 20 percent from 2005 levels by 2020. It sets a low carbon fuel standard calling for a 5 percent cut in the carbon content of transportation fuels by 2015 and 10 percent by 2020.

The legislation also directs the EPA and the Army Corps of Engineers to set aside funds for restoration and protection activities "in large-scale estuarine ecosystems, such as Chesapeake Bay and Long Island Sound" that would be impacted by climate change.

Sen. Barbara Boxer, D-CA, the committee's chairwoman, called the legislation "historic."

Sen. Ben Cardin, D-MD, who also serves on the committee, said "climate change is a real problem in this world that craves American leadership. This legislation exercises the international leadership necessary to level the environmental playing field around the globe."

But the bill's prospects are anything but certain. Many Republicans have vowed to seek significant changes when it comes up for action on the Senate floor this year.

Sen. James Inhofe of Oklahoma, the ranking Republican on the committee, has promised a filibuster, meaning it will take 60 votes to be approved.

The bill's supporters, particularly Boxer, took care to avoid any major changes in the carefully crafted bill. One amendment after another was rejected, most by an 11-8 vote-seven Democrats, two independents and Warner voting in unison.

Aside from Warner, Republicans argued that additional safeguards should be included to ensure against economic hardship.

"This is going to cost a ton of money" in higher energy costs, said Sen. George Voinovich, R-OH. He argued that safety valves are needed "if this thing goes off the cliff."

Republicans offered a string of defeated amendments that would ease or lift the emissions reduction requirements if they severely impacted poor people, if technologies were unavailable or if other countries such as China and India did not approve similar measures.

Boxer rejected the notion that the emission limits-as Voinovich maintained-amounted to "a pervasive intrusion" on private business. She listed major corporations-oil companies, auto makers and electric utilities, among others-that have endorsed mandatory emission limits to deal with global warming, although not all are in favor of the Senate bill.

Environmental groups have generally endorsed the legislation.

Doug Siglin, Chesapeake Bay Foundation federal affairs director, called the bill "a significant step forward in the United States' effort to reduce the effects of climate change and sea level rise." He added the group is "particularly pleased that the bill allocates a significant amount of funding derived from its emission allowance auction to states and federal agencies in the Chesapeake Bay region to help mitigate the impacts to aquatic and terrestrial wildlife and habitats."