By David Shukman
Environment correspondent, BBC News, Bonn
There are demands for China and India to commit to cutting emissions
Time is running short to agree a new treaty on global warming amid deep divisions over key issues, according to the UN's top climate official.
Speaking at the start of the latest round of UN discussions, Yvo de Boer said the political signals were positive, but progress still too slow.
About 1,000 officials are meeting in Bonn for a week of informal talks.
The aim is to clear the way for the adoption of a new UN climate treaty in Copenhagen in December.
"We've got a 200-plus-page text riddled with square brackets (where issues are unresolved)," Mr de Boer told BBC News. "And it worries me to think how on earth we're going to whittle that down to meaningful language with just five weeks of negotiating time left."
Facing delegates is a large digital clock counting down the days to the start of the Copenhagen summit - 119 as of today.
But Mr de Boer warned: "You're looking at hugely divergent interests, very little time remaining, a complicated document on the table and still a lot of progress to be made on some very important issues like finance."
One of the toughest disputes is over which countries should commit to reducing their levels of greenhouse gases.
The industrialised nations say that big polluters in the developing world, notably China and India, must be included in any treaty commitments.
The head of the US delegation here, Jonathan Pershing, said that having those two countries included was "absolutely part of the deal".
"We see success in Copenhagen as in no small measure a function of what all these major players do," he told BBC News. "Ourselves, Europe, China, India, Japan - it has to be the major emitters. If we think of a group of about 15 countries, they comprise on the order of 75% of global emissions.
"We can't solve this without them; you need them all and they all have to move immediately."
But developing countries point out that most of the greenhouse gases in the atmosphere came from the industrialised world; whereas societies such as India remain desperately poor.
"[India] is a country where half the rural population does not have a light bulb in its home or a gas ring," said Ambassador Chandrashekhar Dasgupta, the senior Indian negotiator here.
"So to describe this country as a large emitter is absurd - there's no other word for it."
Another source of tension is over finance - the help the developing world says is needed to cope with the effects of climate change.
Bernaditas de Castro-Mueller of the Philippines is a senior co-ordinator for the G77 group of developing countries.
She told me that the nations that had caused the most greenhouse gases had an obligation to help those suffering from them.
"It's just an outrage that countries cannot live up to their responsibilities. We're all parties to this convention, including the developed countries," she said.
This week's talks are billed as informal in an effort to foster some breakthroughs. They are not likely to provide answers, but may signal whether a treaty is achievable by December's deadline.