UN Secretary-General Ban Ki-moon said Monday that climate is "a leading political and economic problem" and "it's time to act" to respond to the problem.

Ban told his monthly press conference here that he also called upon world leaders "to double their efforts" to reach "a comprehensive, fair agreement (in Copenhagen) that can be turned into a legally binding treaty."

"I appeal to all world leaders to lead and to redouble efforts to find room for compromise," he said. "Time is running out. There is no time left for posturing or blaming. Every country must do its part to seal a deal in Copenhagen."

"If everything is left to leaders to resolve at the last minute, we risk having a weak deal -- or no deal at all. And this would be a failure of potentially catastrophic consequence," he said.

The secretary-general, in answering the press questions, denied the allegations that the Copenhagen process has collapsed, saying that negotiations are still going on and a legally binding treaty will be reached next year.

The secretary-general voiced confidence in a successful outcome as he himself prepares to leave to join the summit, citing new commitments from industrialized countries, emerging economies and developing nations, and deploring recent efforts to derail progress by those who try to claim that the science about climate change is unconfirmed.

Ban acknowledged that the negotiations are difficult and complex -- "among the most ambitious ever to be undertaken by the world community" -- and noted the strong passions and hard bargaining under way.

"But we also see tangible progress on core issues of technology cooperation and financing. We have reached substantial agreement on 'fast track' funding for mitigation and adaptation," he said.

Progress has been made in the first week of talks, but negotiating groups are still wide apart on some key issues, such as emission cuts by developed nations and financial support for developing nations, Chinese Vice Foreign Minister He Yafei told Xinhua on Sunday in the Danish capital.

The secretary-general said that he is scheduled to fly to Copenhagen, the Danish capital, to attend the high-level talks on climate change, where he is expected to appoint Wangari Maathai, a Nobel Peace Prize winner, to be the UN Peace Messanger on the issue of climate change.

"Professor Maathai's long record of achievement in environmental conservation and sustainable development makes her an excellent choice," Ban said.

At the start of the most critical week in global efforts to forge a new deal to curb climate change, Ban warned that the world stood at the crossroads between a sustainable future and a path to catastrophe.

"Now is the moment to act," he said. "Seldom in history has a choice been so clear. We can move toward a future of sustainable green growth, or we can continue down the road to ruin. We can act on climate change now, or we can leave it to our children and grandchildren -- a debt that can never be paid, a poisoned legacy that threatens our planet and its people."

UN officials have said there are three key layers of action that governments must agree to in the course of the Copenhagen summit: fast and effective implementation of immediate action on climate change, ambitious commitments to cut and limit emissions, including start-up funding and a long-term funding commitment, and a long-term shared vision on a low-emissions future for all.

"Looking ahead, we need greater clarity on a robust finance package for the middle and longer-term," he said. "It is essential that we leave Copenhagen with a clear understanding of how we will meet the financing challenge through 2020."

"It is the members states who negotiate and propose solutions," he said. "The United Nations and me as the secretary-general are to provide a forum" for all member states to find convergence on the issue.

Government ministers were arriving in Copenhagen over the weekend to work for an agreement on two draft texts that emerged from a week of discussions at the UN climate talks amid expectations that negotiators from more than 190 countries will seal a deal to fight climate change.

At a UN panel of climate, scientists were proposing a 25-40 percent cut in carbon emissions by rich nations by 2020 in order to put global warming under control, but the commitments made so far by developed countries collectively amount to only a 16-18 percent cut, the Chinese vice minister said.

For funding, UN data put developing nations' needs at 100 billion U.S. dollars annually to cope with the impact of climate change, but rich nations were proposing only 10 billion dollars in the next three years and no mid-term and long-term targets were offered, he added.

The Copenhagen conference is officially known as the 15th Conference of the Parties of the United Nations Framework Convention on Climate Change (UNFCCC), and it will conclude on Dec.18.