OTTAWA – Prime Minister Stephen Harper brushed off criticism on Friday that Canada would act on climate change only in parallel with the United States, saying this was crucial because of North America's economic integration.

"If the Americans don't act, it will severely limit our ability to act, but if the Americans do act, it is absolutely essential that we act in concert with them," Harper told a news conference in Copenhagen at the end of a U.N. climate summit.

He said the Conservative government's strategy was "a big departure" from the previous Liberal government's approach at the 1997 Kyoto talks on climate change.

"The previous government said that they would go ahead and implement a regulatory regime in Canada even if the United States did not do so," Harper said.

Opposition Liberal leader Michael Ignatieff said in Ottawa on Friday that Canada should not effectively let its public policy be set by Washington, and has criticized delays in the Harper government's plans to impose regulations on industry.

Harper said the government's position was that it would put the Canadian economy at a disadvantage to go it alone.

"The nature of the Canadian economy and the nature of our integrated energy markets is such that Canada and the United States need to be harmonized on this, so obviously we are working with the Obama administration and will be continuing to adjust our plans in terms of what is being planned in the United States," he said.

Harper had originally advocated reductions only in the intensity of carbon emissions, meaning cutting the amount emitted per unit produced, but he insisted that the approach now was for absolute reductions going forward.

Regulation of Canada's huge oil sands, slammed by environmental activists for their greenhouse gas emissions, will be essential, he added.

Harper also said Canada was ready to contribute funds to help poor countries combat climate change, particularly to the poorest and most vulnerable nations.