Day One has come to an end at the biggest and most important UN conference on climate change in Copenhagen. There is an unmistakable sense of unity and political determination hanging in the air.

 

Optimism -- that is the overall impression that first comes to mind as the UN's top climate expert and conference president contemplates the first round of talks in Copenhagen.

Connie Hedegaard, Conference President, said, "I have never seen anything like it, when it comes to political will, and I also take that the political will will never be bigger than when we have sort of the chance to benefit from. "

One hundred and ten heads of state or government have said they will attend the end of the conference in two week's time.

Yvo De Boer, Executive Secretary, UN Framework Convention on Climate Change, said, "I believe that this conference has already written history, that this conference will write history. But we need to make sure that it writes the right history."

The two-week conference, unprecedented in its scale and ambition, convened in an upbeat mood after a series of promises by rich and emerging economies to curb their greenhouse gas emissions.

The US has pledged to cut emissions about 17 percent by 2020.

China has vowed to curb the intensity of its carbon emissions by 40 to 45 percent per unit of GDP by 2020.

India has said it is likewise prepared to cut emissions intensity 20 to 25 percent by 2020.

Russia's goal is a 40 percent improvement in energy efficiency by 2020, but the country is willing to reduce emissions between 20 and 25 percent from 1990 levels.

The 27-member EU aims to take action that will limit global warming to two degrees Celsius. The bloc says it will cut carbon dioxide emissions 20 percent by 2020 from 1990 levels.

Yvo De Boer, Executive Secretary, UN Framework Convention on Climate Change, said, "If you look at the announcement that was made by China alone, that accounts for about 25 percent of the emission reductions that we need to see in order to avoid a more than two degree temperature increase. So, very significant commitments are being made by the developing countries."

Still, major issues have yet to be resolved.

At stake is a deal that aims to wean the world away from fossil fuels and other pollutants to greener sources of energy, and to transfer hundreds of billions of dollars from rich to poor countries every year over decades to help them adapt to climate change.

The first week of the conference will focus on refining the complex text of a draft treaty.

But major decisions will await the arrival of environment ministers and heads of state in the final days of the conference.