Governments at a key UN climate summit will discuss how to reduce greenhouse gas emissions after the current Kyoto Protocol targets expire in 2012.
Talks will centre on whether a further set of binding targets is needed.
It is the first such meeting since the Intergovernmental Panel on Climate Change (IPCC) warned that evidence for global warming was "unequivocal".
The two-week gathering in Bali, Indonesia, will also debate how to help poor nations cope in a warming world.
The annual high-level meeting, organised by the UN Framework Convention on Climate Change (UNFCCC), is under pressure to deliver a new global agreement on how to cut rising greenhouse gas emissions.
Rachmat Witoelar, the Indonesian environment minister who was named president of the conference, pledged to do his best to deliver a deal.
"Climate protection must form an integral part of sustainable economic development, and it is critical that we act and we act now," he said.
UNFCCC Executive Director Yvo de Boer urged the international community to use the summit to take "concrete steps" towards curbing climate change.
"We urgently need to take increased action, given climate change predictions and the corresponding global adaptation needs," he said in his welcome message to delegates.
"In the context of climate change, projections of economic growth and increases in energy demand over the next 20 years, especially in developing countries, point to the urgent need to green these trends."
Earlier this year, the IPCC published its Fourth Assessment Report (A4R), in which it projected that the world would warm by 1.8-4.0C (3.2-7.2F) over the next century.
Mr de Boer added that the IPCC's conclusion that climate change was "very likely" the result of human activity ended any doubt over the need to act.
Climate for consensus?
At the top of the conference's agenda is the need to reach a consensus on how to curb emissions beyond 2012.
This marks the end of the current phase of the Kyoto Protocol, which commits industrialised nations to cutting greenhouse gas emissions by an average of about 5% from 1990 levels.
Critics of the existing framework say binding targets do not work, and favour technological advances instead.
Recent studies show that levels of carbon dioxide in the atmosphere are rising faster than they were a decade ago.
Meanwhile, US President George Bush - who favours voluntary rather than mandatory targets - issued a statement saying that the nation's emissions had fallen by 1.5% in 2006 from levels in 2005.
Mr Bush used the reduction as an endorsement of his climate policy, saying: "Our guiding principle is clear: we must lead the world to produce fewer greenhouse gas emissions.
"We must do it in a way that does not undermine economic growth or prevent nations from delivering greater prosperity for their people."
However, the European Union backs the use of binding targets. The 27-nation bloc has already committed itself to cut emissions by 20% by 2020.
A number of observers believe the difference between the two economic powerhouses will result in the Bali conference failing to deliver a policy roadmap for "Kyoto II".
Softening the blow
The conference is also scheduled to consider how to fund projects that will help developing nations deal with the impact of climate change.
Ahead of the climate conference, another UN agency published a report criticising global efforts to date.
The UN Development Programme's annual Human Development Report said funding currently amounted to $26m (£13m), roughly the same amount as the UK spent on its flood defences in a week.
"Nobody wants to understate the very real long-term ecological challenges that climate change will bring to rich countries," said lead author Kevin Watkins.
"But the near-term vulnerabilities are not concentrated in lower Manhattan and London, but in flood-prone areas of Bangladesh and drought-prone parts of sub-Saharan Africa.
"Allowing the window of opportunity to close would represent a moral and political failure without precedent in human history."
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