A series of reports last year from the UN's Intergovernmental Panel On Climate Change highlighted the urgent need to curb emissions blamed for causing global warming.
One report said it was more than 90 per cent certain that human actions - mainly burning fossil fuels - were to blame for changes to the weather system that will bring more heat waves, droughts, storms and rising seas.
Yvo de Boer, UN climate chief, said that negotiators faced a "daunting task" balancing competing interests from each country.
The world has "considerably less than two years to craft what may well, in the end, be one of the most complex international agreements that history has ever seen," de Boer told reporters.
'Winners and losers'
"Clearly in the process there will be winners and there will be losers. But it is also clear that if we fail to act, then we will all be losers in the end."
De Boer, executive secretary of the UN framework convention on climate change, said the Bangkok conference should identify which areas needed work and set up new sessions or studies to ensure a deal by the end of next year.
Speaking in a video message at the start of the conference on Monday Ban Ki-moon, the UN secretary general, called on the 1,000 delegates to work hard in reaching a compromise.
"The world is waiting for a solution that is long-term and economically viable," he said.
The talks are designed to replace the 1997 Kyoto global warming pact after its first phase expires in 2012.
UN studies show global warming is disrupting
the world's weather systems [GALLO/GETTY]
The US was the main opponent of the Kyoto Protocol and has remained sceptical about the terms outlined at last year's Bali meeting.
George Bush, the US president, argued that Kyoto was unfair by requiring only wealthy countries to slash greenhouse gas emissions blamed for global warming.
Fast-growing developing economies such as China and India argue that they cannot be expected to make the same type of cuts as rich ones.
They also want technology from rich countries to help them curb emissions.
'Only a beginning'
Yu Qingtai, China's chief negotiator, said: "Bali was a successful meeting, but only a beginning to the process.
"We want this meeting to set a positive tone for the next two years."
The European Union has pledged unilaterally to cut emissions by at least 20 per cent by 2020 compared with 1990.
But the 27-nation bloc has experienced internal feuding on how to meet the goal.
Coal-rich Poland, for example, wants to ensure a future for fossil fuels.
Angela Anderson, global warming director at the Washington-based Pew Environment Group, said: "Every country comes at this now trying to figure out what's in their individual interests as well as the global interests.
"There is a lot of housekeeping to do at this meeting to figure out how they are going to proceed."
No major decisions are likely from the Bangkok talks, which are intended mainly to establish a timetable for more rounds of talks culminating in the signing of a new treaty at a UN climate change conference in Copenhagen at the end of next year.