Opposition parties came out swinging at Prime Minister Stephen Harper's refusal to sign on to a Commonwealth climate change deal Monday, saying Canada is out of step with the rest of the world.

Liberal Leader Stéphane Dion accused Harper, who didn't sign a weekend deal calling for binding cuts to greenhouse gas emissions, of ignoring the "worst ecological threat known to humanity."

"Instead of leading by example, he engaged in sabotage at the conference," said Dion. "Why is he leading Canadians in a race to the bottom?"

During the weekend meeting in Uganda, Canada and Australia opposed a proposal calling on developed Commonwealth countries to meet the binding targets. Without consensus, the Commonwealth was blocked.

Harper argued Canada wouldn't support any deal unless it imposed binding targets on some of the world's biggest polluters like the United States, China and India.

Liberal deputy leader Michael Ignatieff said Harper had turned his back on the 53-member Commonwealth.

"When the Commonwealth turned to Canada and asked to commit to binding targets, Canada looked away," said Ignatieff.

Bloc Québécois Leader Gilles Duceppe chided Harper for calling the Kyoto Protocol "a mistake" that shouldn't be repeated.

"Isn't he showing his true colours, that's he's a champion of oil industry and he's using all his political clout to counter any real climate change plan," said Duceppe.

Environment Minister John Baird, who repeatedly accused the former Liberal government of failing to tackle climate change during its time in power, said Harper is taking a strong stand on the issue.

"We're not prepared to let the big emitters off the hook," said Baird. "We need everyone with an oar in the water rowing together."

The targets would have been meaningless without a wider international deal, he said.

"This is a crisis of environmental and world proportions," said Baird. "We need all hands on deck. We need all countries to accept binding targets so we can get the job done for our planet."

With files from the Canadian Press