Representatives from more than 190 nations have begun talks in Bali in an effort to agree a timetable for negotiating a successor to the Kyoto Protocol on global warming.
It is hoped a consensus can be reached on concluding talks by 2009.
The UN's main climate change official, Yvo de Boer, warned delegates before talks began in Indonesia that impacts of global warming, like droughts and rising sea-levels, are already visible.
Mr de Boer said the world has two years to conclude talks on a successor to the Kyoto Protocol.
The key to success will be getting all countries to sign-up to a deal cutting dangerous greenhouse gases, from big emitters like Europe, to emerging economies like China, and developing countries in Africa.
The main hurdle will be finding a way of getting countries to urgently cut their carbon dioxide output, despite significant concerns this will jeopardise economic growth.
There is optimism in Bali that a roadmap for talks will be secured, but concluding a deal by 2009 may be difficult.
Meanwhile Australia's newly elected Prime Minister, Kevin Rudd, has begun dismantling the former government's policies by ratifying the Kyoto Protocol on climate change.
'This is the first official act of the new Australian government, demonstrating my government's commitment to tackling climate change,' he said.
