Secretary-General Ban opened high-level talks at the Bali conference by urging delegates from around 190 countries to push toward replacing the Kyoto Protocol by 2009.
The delegates hope to draft what is being called the Bali road map for new negotiations to replace the Kyoto accord, which expires in 2012.
Mr. Ban Wednesday morning called on nations to act swiftly in the fight against global warming.
"We gather because the time for equivocation is over. The science is clear. Climate change is happening, the impact is real, the time to act is now," said Ban.
For 10 days, scientists and mid-level government officials have met in Bali to prepare for three days of talks by senior officials. The major issue of dispute in the talks is whether to include targets for reducing greenhouse gas emissions, which many scientists believe contribute to global warming.