An upcoming round of new talks on climate change must reach a breakthrough in reducing greenhouse gas emissions, the head of the United Nations told a summit of world leaders Monday.

"Today, the time for doubt has passed," Ban Ki-moon told the meeting, at a UN assembly hall in New York.

UN Secretary General Ban Ki-moon, top right, and General Assembly president Srgjan Kerim, left, of Macedonia, listen as California Gov. Arnold Schwarzenegger addresses Monday's climate-change summit.
(Mary Altaffer/Associated Press)

Scientists have "clearly outlined the severity of the problem," said Ban, adding that affordable technologies already exist to begin dealing with the challenge.

"Inaction now will prove the costliest action of all in the long term," the UN secretary general continued.

Nearly 80 heads of countries gathered at UN headquarters in New York for the one-day summit to discuss ways to curb climate change. Leaders, including Canadian Prime Minister Stephen Harper, spoke about what their countries are doing to combat the problem and what new measures can be taken in the future.

The talks are a prelude to the UN Climate Change Conference in Bali, Indonesia, in December, where leaders are to forge a new deal to replace the Kyoto Protocol when it expires in 2012.

"I'm gratified that so many of you have come to this event. By being here you show you share my concern,"  Ban told the leaders as Monday's meeting began.

"This meeting is an opportunity to infuse this process with political momentum," Ban added.

"We need to set the stage for a comprehensive agreement that tackles climate change on all fronts.…Our goal must be nothing short of a real breakthrough in Bali."

Canada to join Asia Pacific talks

After his speech, Harper told reporters that Canada had joined talks with a U.S.-led climate change group formerly called AP6, now known as the Asia Pacific Partnership.

The group, which has been criticized by environmentalists as not setting hard targets to cut greenhouse gas emissions, also includes Australia, South Korea, Japan and major emitters China and India.

"This will be another international forum where Canada can pursue its objectives in terms of fighting climate change," said Harper.

The group, billed as an alternative to the Kyoto Protocol, will meet next in Oct. 15 in Delhi.

Canada not on track to meet Kyoto

Adopted in 1997 and ratified by 141 countries in 2005, Kyoto sets international greenhouse-gas emissions-reduction targets. Different countries have different targets to meet, with Canada scheduled to reduce its emissions below 1990 levels by 2012. Some industrialized countries, such as the United States and Australia, did not sign on.

Canadian Prime Minister Stephen Harper chats with his press secretary, Carolyn Stewart Olsen, as he attends Monday's UN climate change summit.
(Tom Hanson/Canadian Press)

Canada, which signed Kyoto under a previous Liberal government, is not poised to meet its target. Instead, the Conservative government has pledged to reduce the country's overall emissions to 20 per cent lower than 2006 levels by 2020.

Harper reassured leaders at Monday's meeting that he is prepared to join forces with other countries to fight climate change.

"Canada is committed to working with the international community and the United Nations to develop the targets and the technologies that will overcome the challenge of climate change," Harper said after outlining the green technologies Canada is pursuing, like carbon capturing and wind power.

The environmental organization Sierra Club of Canada criticized Harper's appearance as a missed opportunity.

"Canada would like to see their country play a constructive role in this global effort. Yet the prime minister continues to align himself with (U.S. President) George W. Bush on climate policy, undermining international efforts to reduce emissions," Sierra's Emilie Moorhouse said.

California Gov. Arnold Schwarzenegger talked about green technologies at the meeting, outlining the ones his state has embraced. Schwarzenegger said U.S. states are leading the way, while the Bush administration is backing away from establishing emissions caps.

"California is moving the United States beyond debate and doubt to action," Schwarzenegger said. "What we are doing is changing the dynamic."

Bush did not participate in Monday's summit, but was scheduled to meet with some world leaders at a small dinner hosted by Ban on Monday night. Bush organized his own smaller climate change meeting, which will draw world leaders to Washington on Thursday and Friday.

'No nation can address this challenge on its own'

At the UN meeting on Monday, Ban urged countries not to tackle climate change on their own, but to instead work together to come up with creative solutions that promote economic growth.

"Given the nature and magnitude of the challenge ... no nation can address this challenge on its own. No region can insulate itself from these climate changes," he said.

"We need to confront climate change within a global framework, one that guarantees the highest level of international co-operation that is necessary."

The United Nations said Monday's meeting is the largest meeting ever of world leaders on the topic of climate change.

In February, the UN's Intergovernmental Panel on Climate Change released a report on the impact greenhouse gases are having on the Earth.

The report predicted that global warming would cause the average worldwide annual temperature to increase by between 1.8 and four degrees Celsius over the next century, while sea levels would rise between 18 and 59 centimetres over the same time period.

The report also called the proof of global warming "unequivocal" and said the root cause was "very likely" human-produced greenhouse gas emissions.

With files from the Canadian Press