Long-deadlocked UN climate talks are finally starting to shift from procedure to substance only two months before a critical climate summit in Copenhagen, negotiators and green groups said Monday.

"There is definitely a positive dynamic. New York injected a sense of urgency," said Paul Watkinson, head of France's climate negotiation team, referring to the first-ever UN climate leaders' summit two weeks ago.

"Overall there is a new will to move forward," he told AFP.

About 2,000 delegates from 180 countries are half-way through a two-week negotiating session, the next-to-last before December's Copenhagen conference, tasked with delivering a treaty to save the world from the ravages of global warming.

The Bangkok meetings, within the UN Framework Convention on Climate Change (UNFCCC), run until Friday.

For more than two years, the troubled UN talks have been stymied on critical issues dividing rich and poor nations.

They disagree over how to share out the task of slashing greenhouse gases, and how much money developing countries should receive to fight climate change and cope with its impacts.

On Monday, more than 1,000 demonstrators calling for urgent action gathered in front of the conference centre shouting slogans such as "climate justice!" and "rich countries, pay your climate debt!"

Typhoons and tsunamis have caused widespread devastation in Asia over the last 10 days, and many people in the region are for the first time linking some of these natural disasters to the influence of climate change.

Much of the focus at the Bangkok talks is on a 170-page document that everyone simply calls "the text."

Intended as a working draft for the December treaty, the document was "an absolute mess" coming into the meeting and little more than a compendium of conflicted positions, according to UN climate chief Yvo de Boer.

"The main task in Bangkok is to emerge with a text that is streamlined, cleaner and shorter," said Kim Cartensen, head of the WWF Global Climate Initiative. "Negotiators have made progress."

"Constructive things are happening at these negotiations at the expert level," agreed Jennifer Haverkamp, a senior policy analyst at the Washington-based Environmental Defense Fund.

Talks on how to include the management of tropical forests have in particular made progress, she said.

Deforestation accounts for about 20 percent of global greenhouse gas emissions every year, but figuring out how to include the preservation of forests in a larger framework has proved enormously complicated.

Forging a coherent technical document is critical to the success of any future summit-level climate talks, many participants here said.

But despite modest signs of progress, there are fears the issues are simply too complicated and divisive, and the time remaining too short, for negotiators to be able to hammer out a comprehensive climate deal by the year's end.

"You can't have heads of state sit down and have an agreement suddenly emerge. There is a lot of groundwork that has to be laid before political leaders swoop in and make the deal," Haverkamp said.

"There is a lot of stuff that needs to happen this week, and between Bangkok and Copenhagen," added Artur Runge-Metzger, head of the European Commission's climate unit.