BUENOS AIRES, Argentina (CNN) -- One year after the world agreed to a historic pledge to reduce heat-trapping gases, delegates are struggling to figure out the rules to the accord.

In a demonstration outside the Climate Summit meetings in Buenos Aires, environmental activists mocked a key but controversial plank in the global climate control agreement approved last year in Kyoto, Japan.

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CNN's Richard Roth reports on the issues of emissions trading

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It's called "emissions trading," and it allows industrialized nations to meet their greenhouse gas reduction requirements by buying or trading pollution credits from poorer countries with fewer emissions.

Critics say trading emissions will not result in less pollution.

"This is not anti-free trade. It is about ruling out excesses that could wreck the Kyoto protocol," said Stephan Singer of the World Wildlife Fund.

The world's largest polluter, the United States, denies it is trying to trade away its climate control obligations.

U.S. Undersecretary of State Stuart Eizenstat says emissions trading can work.

"It is an economically sensible way of doing it rather than imposing heavy new taxes or top-down regulation. This uses the power of the marketplace."

Ritt Bjerregaard, EU environment minister, is worried that trading will be uncontrolled and prefers a cap and better accounting on emissions trading. "I don't want and the EU doesn't want to have trade without really helping the environment," he said.

Outside, a protester's skit spoofed so-called "hot air" in the climate agreement. Countries such as Russia, which has closed outmoded plants, could exaggerate their gas emissions -- in effect making money through pollution.

Delegates may not settle all bids in this emissions trading fight, delaying a major decision until the next conference a year from now.