"We have to roll our sleeves up and get down to work," Yvo de Boer, the U.N.'s top climate change official, said in an interview Sunday.
In Bali, delegates agreed to conclude a new climate change treaty by December 2009. They later adopted a negotiating timetable at another conference in Bangkok.
Scientists say the world's carbon emissions must peak within the next 10 to 15 years and then fall by half by mid-century to avoid potentially catastrophic changes in weather patterns, a rise in sea levels that would threaten coastal cities and the mass extinction of plants and animals.
The new climate change pact will succeed the first phase of the 1997 Kyoto Protocol, which requires 37 industrialized nations to reduce greenhouse gas emissions an average of 5 percent below 1990 levels by 2012.
Delegates in Bonn will begin work on how to help developing countries adapt to anticipated changes in their climate, on transferring new technologies to help them avoid hefty carbon emissions as they expand their economies, and on how to raise the trillions of dollars required over the next decades to curb climate change.
No one expects answers by the end of the Bonn conference. But de Boer said he hopes this week's discussions will crystalizing ideas. Governments must then submit written proposals to be honed into a draft treaty in intensive negotiations over the next 18 months.