The Environmental Protection Agency is reportedly poised to announce a move to regulate climate-warming pollution as talks get under way today in Denmark aimed at reaching a new international agreement to limit the threat of climate change.

The Associated Press and other national media report that EPA has concluded that "greenhouse gases" are endangering people's health and must be regulated. EPA Administrator Lisa P. Jackson has scheduled "a significant climate announcement" at 1 p.m. today.

The so-called endangerment finding is needed before the EPA can regulate carbon dioxide and five other greenhouse gases released from power plants, factories and motor vehicles under the federal Clean Air Act. A Supreme Court ruling two years ago upheld EPA's legal authority to treat carbon dioxide as a pollutant.

The EPA announcement comes as a United Nations conference on climate change convenes in Copenhagen, with delegates from 192 nations trying to forge a new global agreement to limit greenhouse gases and help nations most likely to be affected by climate change. The outcome of the negotiations is far from certain. 

President Obama, who originally planned to drop in on the talks on Wednesday, now is scheduled to join them near their conclusion on Dec. 18.  He has pledged that the United States will reduce its greenhouse-gas emissions 17 percent below 2005 levels by 2020. That's identical to the interim reduction called for in climate legislation passed by the House earlier this year, and about half of what the US would have been required to do under the earlier climate treaty negotiated in 1997 in Kyoto, Japan, but which the US never ratified.  Climate legislation is stalled in the Senate again, as debate there drags on over health care reform.

Business groups have expressed concern about the impact on small businesses of any EPA move to regulate carbon dioxide and other greenhouse gases like other air pollutants.  The Obama administration has said it would prefer for Congress to approve a "cap and trade" system instead, under which businesses would have to pay for permits to release climate-warming emissions, giving them an incentive to reduce but the flexibility in how and how quickly they do it.

The legislation in Congress also has critics on the left and right, with some environmental groups arguing the cap-and-trade scheme won't reduce greenhouse gas emissions deep or fast enough, while conservatives contend it will harm the U.S. economy and cost jobs as the nation struggles to pull itself out of a deep recession.   The Congressional Budget Office has said the House plan would have "only a small effect in the long run" on overall employment, but would trigger a significant upheaval in jobs as the economy shifts to rely on alternatives to fossil-fuel energy.

Public opinion polls in this country, meanwhile, indicate Americans worries about climate change are weakening, as is support for "cap and trade" legislation.  You can see a selection of poll results here.

(HO/AFP/Getty Images photo of Greenpeace activists deploying a banner in Copenhagen harbor)