The outcome of the historic United Nations climate change conference under way in Copenhagen will have reverberations for the future of humanity and the planet, UN Secretary-general Ban Ki-moon said on Tuesday.

UN Secretary-general Ban Ki-moon speaks at the UN Headquarters in New York, the United States, on December 8, 2009. Ban Ki-moon on Tuesday voiced optimism for a successful international conference in Copenhagen, saying that the gathering can be a "turning point" in the fight against climate change. [Xinhua]

"We've come a long way in just two years' time, but what we do now over the next two weeks (in Copenhagen) will determine how we fare," Ban told reporters at the UN Headquarters in New York.

More than 100 heads of state and government, such as US President Barack Obama and Chinese Premier Wen Jiabao, as well as over 15,000 participants, are set to take part in the event in the Danish capital, where nations are expected to wrap up agreement on an ambitious new climate change deal.

The secretary-general expressed optimism that an immediately effective "robust" agreement, which will include specific recommendations on mitigation, adaptation, finance and technology, will be reached.

"Copenhagen can and must be a turning point in the world's efforts to prevent runaway climate change," he said.

Unprecedented momentum has been drummed up toward clinching a new deal, Ban said. "Never have so many different nations of all size and economic status made so many pledges together."

The secretary-general will travel to Copenhagen next week to open the high-level segment of the gathering, which wraps up on December 18.

The secretary-general told reporters here on Monday that he expected no legally binding treaty to be reached at the end of the Copenhagen conference.

"Our target, our goal, is to have a legally binding treaty ... as soon as possible in 2010," Ban said. "But before that, we must have a strong political agreement in Copenhagen."

"The more ambitious, the stronger agreement we have in Copenhagen, the easier, the quicker the process we will have to a legally binding treaty in 2010, as early as possible," he said. "This is our commitment."

The start of the conference was "very positive and encouraging," with clear calls made for urgent action on climate change, said Yvo de Boer, executive secretary of the UN Framework Convention on Climate Change (UNFCCC).

A real difference will be made in Copenhagen only if it impels significant and concrete action after the conference ends, de Boer told a press conference on Tuesday.

Negotiators, de Boer noted, must hammer out solid proposals on the issues of adaptation, mitigation, finance and technology to underpin an outcome.

He stressed that negotiators must make optimum use of this first week to prepare the groundwork on the issues of adaptation, mitigation, finance, technology, capacity-building and forests. This involves hammering out solid proposals that can constitute the foundations of an agreed outcome in Copenhagen.

The official also voiced confidence that the Copenhagen gathering will end with additional funds provided for developing countries to take action against climate change, with there being growing consensus for swift funding of at least US$10 billion annually from now until 2012.

The Nobel Peace Prize-winning Intergovernmental Panel on Climate Change (IPCC) has found that to stave off the worst effects of climate change, industrialized countries must slash emissions by 25 to 40 percent from 1990 levels by 2020, and that global emissions must be halved by 2050.

The year 2009 will likely be among the 10 warmest since climate records started being taken in 1850 and the 2000-2009 decade is also probably the warmest on record, the UN World Meteorological Organization (WMO) announced on Tuesday.