Climate change experts are meeting in Bangkok for a major conference to discuss ways to combat global warming.
Climate change activists have also gathered for the summit
It is the third such summit this year held by the Intergovernmental Panel on Climate Change (IPCC).
Those attending hope to finalise a report on how the world can mitigate rising levels of greenhouse gases.
A draft version of the report, seen by the BBC, says it is possible to make a real difference, but countries need to implement policies immediately.
Environmentalists argue that while it will need investment to put these policies into practice, the eventual consequences of doing nothing far outweigh the cost of tackling global climate change now.
'Compelling reasons' for change
At least 400 scientists and experts from about 120 countries are attending the third session of the IPCC, the UN's leading body on global warming.
Two reports issued earlier this year by the same UN panel warned that the earth was already warming considerably, and that mankind was almost certainly to blame.
They predicted severe consequences including droughts, floods, storms, heat waves and rising seas.
This third report, which is due to be released on Friday, will lay out ways of reducing greenhouse gas emissions, while taking into account impacts on the economy.
"We look forward to very fruitful days ahead of us, so at the end of the week we can declare we are part of the solution, not part of the problem," Ogunlade Davidson, co-chair of the meeting, told reporters.
"The science certainly provides a lot of compelling reasons for action," Rajendrat Pachauri, chairman of the IPCC, told the Associated Press.
Exactly what action to take, and how much it will cost, is likely to be the main topic of debate during the closed-door meeting.
One of the key issues is the so-called carbon price - a way of making consumers and businesses pay for the pollution they create.
The draft refers to stabilising emissions between 450 and 550 parts per million of CO2 in the atmosphere. Anything less is unrealistic, economists believe.
But correspondents say that both America and China are alarmed by any discussions of a safe limit because it increases pressure to curb their pollution levels.
The draft suggests solutions to mitigate climate change, such as capturing and burying emissions from coal-fired power plants, shifting to renewable forms of energy and more use of nuclear power.
Making buildings more energy-efficient, especially in the developing world, could also lead to significant cuts in global warming, the draft report concludes, as would changes in agricultural practices and reduced deforestation.
The findings of the report will be used by governments and international organisations to map out their own plans for climate change mitigation.
"The IPCC plays an incredibly important role in the political negotiations so people can point and say 'Look, this is what is going to happen in 50 years, these are the options available for us to take actions'," said UN Environment Programme spokesman Michael Williams.
The report's conclusions will play a key role in negotiations on the Kyoto Protocol, which will take place in December on the Indonesian island of Bali.
It will also influence world leaders when they meet face-to-face over climate change at the summit of the group of eight most industrialised nations (G8) in June.