Climate change is an "enormous" problem, but it's "fantasy" to think greenhouse-gas emissions can be cut overnight, Prime Minister Stephen Harper said after a UN report concluded global warming is very likely man-made.

Stephen Harper: 'I don't think realistically we can tell Canadians, Stop driving your car, stop going to work, stop heating your house in the winter.'
(CBC)

The report, released Friday by the Intergovernmental Panel on Climate Change, said human activity was "very likely" the cause of global warming and that higher temperatures and rising sea levels would continue for centuries, regardless of reductions in greenhouse gas emissions.

Canada would be among the countries to see disproportionately high temperatures changes — perhaps enough to keep the Arctic ice-free in summer.

Harper, who was in Ottawa, said climate change requires a long-term solution.

"I think the science is clear that these changes are occurring, they're serious and we must act," the prime minister said.

"The first step in any such plan is to try to stabilize emissions and obviously over the longer term to reduce them.… I think realistically the only way you can get absolute reductions is through the application of new technology over time.

"We have to talk about facts, not about fantasy."

Harper said the government "has the intention to act" on climate change, but must find realistic solutions.

"I don't think realistically we can tell Canadians, 'Stop driving your car, stop going to work, stop heating your house in the winter.'"

Earlier in the day, Environment Minister John Baird acknowledged that the consequences of climate change could be particularly dire for Canada.

Opposition calls for Kyoto targets to be met

In the House of Commons, opposition critics pressed ahead with a Liberal bill that would require the government to fulfil the target of the Kyoto Protocol, a six per cent cut from 1990 levels by 2012.

'I don't know if the prime minister has even read the Kyoto Protocol.' —Liberal environment critic David McGuinty

"I don't know if the prime minister has even read the Kyoto Protocol," Liberal environment critic David McGuinty said.

The Harper government's proposed clean air act is currently under review by a special Commons committee after opposition parties vowed to vote against it if it reached the floor.

The Tory bill would start reducing smog by 2010, but plans four years of discussions with industry on climate change.

Under the proposed plan, there would be no hard caps on greenhouse gas emissions until 2020 at the earliest, but the government would seek to cut emissions by between 45 per cent and 65 per cent by 2050.

The Intergovernmental Panel on Climate Change, created by the United Nations in 1988, releases its assessments every five or six years, and is used as a major source of information for government policy makers.

The 2007 report was backed by hundreds of scientists and representatives from 113 countries.

With files from the Associated Press