The United States will propose an emissions reduction target at a U.N. climate change summit in Copenhagen next month, the White House said Monday.   

An administration official said that a decision will be made soon on whether President Obama will attend the  meeting, at which the attending nations plan to map a strategy to combat global warming.  

China and the United States are the world's top two carbon polluters, according to the World Resources Institute.  The European Union on Monday urged the two nations to commit to new targets at the Copenhagen summit. 

Swedish Prime Minister Fredrik Reinfeldt called both nations' refusal to commit "untenable." Inaction "does not solve the threat of climate change," he wrote on an EU Web site.

The EU has pledged to cut greenhouse gas emissions by 20 percent below 1990 levels to 30 percent if others follow suit. By 2050, it wants to eliminate most emissions, with a target of up to 95 percent. 

Congress has stalled on climate change legislation as it battles over health care. That leaves the world body unlikely to reach a legally binding agreement at the summit, and instead aiming for political commitments.

Obama said during his trip to Asia last week that the U.S. and China want the Copenhagen summit to lead to an agreement that has "immediate operational effect."

We "agreed to work toward a successful outcome in Copenhagen," Obama said after his meeting last week with Chinese President Hu Jintao.

"Our aim there is... not a partial accord or a political declaration, but rather an accord that covers all the issues in the negotiations and one that has immediate operational effect."

Monday's White House announcement came as Michel Jarraud, the head of the U.N. World Meteorological Organization, reported that concentrations of greenhouse gases are at their highest levels ever recorded and climbing. 

Scientists who support climate change theories say the rise in temperatures expected in coming decades demands urgent action, but skeptics are arguing that the evidence is being manipulated by a group of scientists who seek to benefit.

About 1,000 e-mails and 3,000 documents covering a decade's worth of exchanges among the leading scientists were stolen last week from England's University of East Anglia Climatic Research Unit. The materials were posted on Web sites and seized on by climate change skeptics.

Kevin Trenberth, of the U.S. National Center for Atmospheric Research in Colorado and the lead author of the U.N.'s 2001 and 2007 Intergovernmental Panel on Climate Change assessments, is among a group whose private e-mails were recently stolen by hackers and posted online.

Trenberth, who saw many of his e-mails posted, said he believes leaks may have been aimed at undermining next month's summit. 

"It is right before the Copenhagen debate, I'm sure that is not a coincidence," Trenberth said.

The Associated Press contributed to this report.