The Danish presidency of the climate summit in Copenhagen has
sought to play down expectations of a comprehensive deal emerging from the
meeting.
Officials said progress could be made, but an international agreement may have
to wait until a 2010 meeting in Mexico.
US Secretary of State Hillary Clinton told the meeting her country was
prepared to work towards mobilising $100bn a year for developing countries.
The deadlock in talks at the climate summit has now been broken.
Yvo de Boer, executive secretary of the UN's climate body, called the
resumption of negotiations "very encouraging".
But summit hosts Denmark had to drop plans to propose new draft texts on
Thursday after opposition from many developing nations.
A source told the Danish newspaper Politiken: "We are fighting like mad
and we haven't given up, but we will need help from world leaders. They must
put their money where their mouth is. Otherwise it'll be very difficult."
Developed and developing nations remain at odds over who should cut
emissions, how deep the cuts should be, and how much aid should go to poor
countries.
Brown: Climate 'greatest' challenge
But there has been some progress - wealthy nations pledged new funds to
bankroll adaptation to climate change.
On Thursday, Mrs Clinton told delegates: "In the context of a strong
accord in which all major economies pledge meaningful mitigation actions and
provide full transparency as to those actions, the US is prepared to work with
other countries towards a goal of mobilising $100bn a year to address the needs
of developing countries."
She made it clear - as did Japan on Wednesday when announcing a specific
figure for assistance - that the money was contingent on reaching a global deal
here that met its criteria.
BBC environment correspondent Richard Black said developing countries are
likely to point out that there is no figure for what the US is prepared to
provide itself, either from public or private finance.
The sum is also less than the amount that UN agencies such as the World Bank
and International Energy Agency calculates is necessary to help mitigation and
adaptation in the developing world.
At least 130 world leaders are due to join the talks on Thursday, hoping to
sign a new climate pact on Friday.
Addressing the summit on Thursday, Australian Prime Minister Kevin Rudd said
he feared "a triumph of form over substance" at the outcome of the UN
climate summit.
In his speech, UK Prime Minister Gordon Brown urged the summit to
"summon up the greatest level of ambition".
"The success of our endeavours depends on us forging a new
alliance," he told delegates.
He added: "In these few days in Copenhagen which will be blessed or
blamed for generations to come, we cannot permit the politics of narrow self-interest
to prevent a policy for human survival."
Taking charge
US President Barack Obama has been due to attend the final day of the
meeting on Friday, when world leaders will try to lay out a strategy to deal
with climate change after the end of 2012, when obligations run out under the
landmark Kyoto Protocol.
But asked about rumours that President Obama might not attend, Mrs Clinton
said: "The President is planning to come tomorrow. Obviously we hope there
will be something to come for."
Announcing the resumption of talks, Mr de Boer told reporters that
negotiators would consider two negotiating texts; one looking at further
emission cuts by developed nations (except the US) by 2020, and another that
looks at committing all nations to curbing climate change.
Mr de Boer added that the texts will be considered by two working groups,
which were expected to report back to the main conference on Thursday evening.
Saleemul Huq, senior fellow in cliamte change at the International Institute
for Environment and Development told BBC News: "The negotiation process is
in a high state of confusion."
"On the other hand, heads of state are arriving and talking to each
other, and within hours every important decision-maker on the planet will be in
the same town at the same time.
"If they can't do it, no-one can - and I think that they will."
Danish Prime Minister Lars Loekke Rasmussen has taken charge of the
Wednesday-Friday segment involving heads of state and government.
Developing countries, led by China, accused host Denmark of a lack of
transparency by suggesting language for the agreement without full consultation
by all sides on the 193-nation summit.
And China told participants that it saw no chance of reaching an operational
accord this week, an unnamed official told Reuters news agency.
Containing emissions to a level associated with a temperature rise of no
more than 2C is the stated aim of the big nations here.
As things are going they will miss that target by a considerable margin, our
correspondent says.
The poorest and most vulnerable nations say emissions should be contained to
a level associated with a temperature rise of 1 or 1.5C.
They have no chance of getting their way, our correspondent adds.
On a more promising note, Japan promised poorer nations $15bn (£9bn) over
three years if a deal is made.
The amount - payable from 2010-2012 - adds to the $10.6bn (£6.5bn)
commitment over three years made by EU leaders at their summit last week.
Another pledge came from a six-member group - Australia, France, Japan,
Norway, the UK and US - which will collectively commit $3.5bn over three years
to combat deforestation.