COPENHAGEN–The Yes Men forced Canada to say no.

No, it would not adjust its planned emissions cuts to make them the toughest in the world. And no, it would not commit $13 billion, and much more in the coming years, to help the world's poorest countries adapt to the ravages of a warmer planet.

It was this activist group, using the social media they have employed to undermine governments, corporations and other powerbrokers, that brought Canada to its knees at the Copenhagen conference Monday.

In a sophisticated stunt, they forced Canada to explain that it was not, contrary to emails sent to thousands of reporters here, answering the calls of environmentalists, Canadian provinces and countries around the world to take on more ambitious plans to cut greenhouse gases.

"The idea was to confuse the Canadian government, which set up a war room to positively spin their position in the debate even though everyone knows that their position is a cruel joke," Yes Men member Mike Bonanno told the Associated Press.

The elaborate hoax involved fake versions of websites for the Wall Street Journal, Environment Canada and the United Nations, and press conferences staged with fake negotiators from Uganda that provoked real federal officials to lash out at those they suspected of masterminding the campaign of shame.

"You think this is a game, but it's not a game. It's a serious issue," said Prime Minister Stephen Harper's spokesman, Dimitri Soudas, in a heated exchange with a prominent environmental activist that was caught on television cameras.

"More time should be dedicated to playing a constructive role instead of childish pranks," said Soudas.

But Soudas had the wrong man.

It wasn't Steven Guilbeault, co-founder of Équiterre, whom Soudas accused of "criticizing from the bleachers."

"I'm speechless," said Guilbeault. "Why would I do that? It's not what I do, it's not how I do it," he told The Canadian Press.

Guilbeault confronted Soudas at the conference and asked for an apology, but was instead told by Soudas that it was Guilbeault who should apologize for criticizing Canada at an international summit.

The Yes Men on Tuesday are expected to speak more about the stunt, a version of which they have used in the past to shame "big-time criminals in order to publicly humiliate them."

"Targets are leaders and big corporations who put profits ahead of everything else," the group says on its website.

The prank began to unfold around midday with an out-of-the blue announcement that Environment Minister Jim Prentice would be budging from Canada's much criticized plan to cut emissions by 20 per cent from 2006 levels by 2020.

Replacing that would be the most ambitious emissions targets in the world – to cut greenhouse gases by 40 per cent below 1990 levels by 2020, and 80 per cent by 2050. The fake announcement also pledged to give $13 billion a year, or 1 per cent of Canada's gross domestic product, and up to 5 per cent of national income by 2013, all to Africa.

What followed were waves of congratulations for the faux show of Canadian leadership from Uganda and mock press releases from the government in a prank that was unveiled on so many levels that it was hard to keep track of what was real and what was not.

"It is the height of cruelty, hypocrisy and immorality to infuse with false hopes the spirit of people who are already, and will additionally, bear the brunt of climate change's terrible human effects," Prentice was quoted as saying in a second fake news release email.

What he really said was quite different. He denounced "things going on on the periphery of these negotiations," in a daily press conference flooded with international reporters. Stories on the prank were published in the United States, China, Britain, France and elsewhere around the world.

"There are other things that will continue to happen that will be undesirable here, including press releases that are a hoax," Prentice predicted, while stating that he was focused on the negotiations at hand.

All of this unfolded on a day marked by deadlock in talks toward coming up with a new deal to cut global emissions after the objections of the developing nations led to a breakdown in negotiations.

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But even if the stunt that played out at Canada's expense had been the real federal position it wouldn't have nudged negotiators back to the bargaining table.

Sudanese negotiator Lumumba Di-Aping, the head of the G77-China bloc, which represents some 130 nations, said the position presented in the press releases was "still well below what will save Africa by huge margins."

To please the developing world, Canada and its rich-world partners need to agree to limit global temperature rise to 1.5C and cut the amount of carbon in the atmosphere to 350 parts per million from its current rate of saturation, 387 ppm. "Canada has to accept there must be substantial commitment. Canada has been one of the most non-compliant (Kyoto-bound developed) countries and they have to change that."