Prime Minister Stephen Harper said Friday that Canada "must act" to curb global warming after a newly released report that warns humans are "very likely" the cause of the problem.

"The problem is enormous. It's large, it's long-term and there are no quick fixes to this," Harper told reporters in Ottawa.

"You can't just snap your fingers and reduce Canada's energy use by one-third in the space of a couple of years."

The report, compiled by 1,200 world-renowned scientists who are part of the UN's Intergovernmental Panel on Climate Change (IPCC), says more droughts, heat waves, rains and a slow gain in sea levels could last for more than 1,000 years.

The "very likely" involvement of humans, resulting from the burning of fossil fuels, is about a 90 per cent certainty, says the report.

The conclusion is the strongest ever, making it almost impossible for bureaucrats to blame the changes on natural forces.

"I don't think there's ever been as much pressure on governments as we're seeing right now and on humanity to change our habits," said CTV's London Bureau Chief Tom Kennedy.

Achim Steiner, head of the UN Environment Programme, said governments have no excuses left.

"February 2, 2007 may be remembered as the day the question mark was removed from whether (people) are to blame for climate change."

Harper said the only way to achieve absolute reductions was through the applications of new technologies over time.

"I don't think realistically we can tell Canadians -- stop driving your car, stop going to work, turn your heat off in the winter -- we need to adapt to new energy realities so that we can achieve emissions targets."

The report was released Friday at a climate change conference in Paris, which Environment Minister John Baird was attending, and will serve as a summary for policymakers around the world.

"We've clearly got to take action," said Baird from Paris. "I think Canadians don't want to hear what can't be done but they want to hear what action will be taken by their government and we hear that call."

Baird said the Conservatives will be moving forward on two fronts.

"The biggest action we can take is to begin to regulate industrial greenhouse gas emissions," he said. "We also want to, at the same time, deal with this huge challenge of greenhouse gassing and the immediate threat of air pollution, smog and air quality in Canada."

Report findings

The report says the range of possible temperature increases this century is between 1.1 and 6.4 degrees Celsius -- up from the 1.8 to 5.4 degrees estimated in the panel's 2001 report.

For the first time, the report gives a "best estimate," indicating greater certainty than before, that says temperatures will rise between 1.8 to 4.0 Celsius by 2100.

The panel also approved wording saying man-made global warming can "more likely than not" be blamed for an increase in hurricane and tropical cyclone strength since 1970.

In 2001, the same panel had said there was not enough proof to reach such a conclusion. That report also said that global warming was "likely" caused by humans.

The latest report also projects that sea levels could rise between 18 and 59 centimetres in this century. Meanwhile, the IPCC also concluded that even higher levels remain a possibility in Antarctica and Greenland.

Wording of the new report required consensus from all countries, including the United States and oil-rich countries such as Saudi Arabia.

Some delegates told AP that Chinese officials expressed opposition to strong wording on the global warming statement.

The 1,200 scientists who directly prepared the report represent 40 different countries.

However, more than 2,300 scientists were involved in the process for the panel which is made up of 113 countries.

The Kyoto Protocol is the main plan in place to help cap emissions of greenhouse gases until 2012; however, it has been weakened by the pull out of the U.S. -- the top contributor to greenhouse gases.

With files from The Associated Press and The Canadian Press