Day Three of the United Nations Climate Change Conference 2009

The U.S. and China exchanged barbs Wednesday at the Copenhagen climate talks, underscoring the abiding suspicion between the world's two largest carbon polluters about the sincerity of their pledges to control emissions.

U.S. chief negotiator Todd Stern urged China to "stand behind" its promise to slow the growth of the country's carbon output and make the declaration part of an international climate change agreement.

President Obama's top climate change negotiator arrived in Copenhagen Wednesday swinging back at Chinese demands for the United States to increase its emission reduction goals.

"With respect to our emissions, it's true our emissions have gone up since 1990," Todd Stern acknowledged. But he added, "the country whose emissions are going up, dramatically, really dramatically is China."