Documents leaked at the UN climate summit reveal divisions between industrialised and developing countries over the shape of a possible new deal.
Campaigners say a draft text proposed by the Danish host government would disadvantage poorer nations.
It also sees everything coming under a single new deal, whereas an alternative text from developing countries wants an extension to the Kyoto Protocol.
Other blocs are expected to release their own texts in the next few days.
Chairmen of working groups will then have to turn the various documents into a political document that 100-odd world leaders, plus delegates representing all other nations, could sign at the end of the conference.
The Danish document, plus the alternative text submitted by the BASIC group (Brazil, South Africa, India and China) were discussed by a small group of key countries in Copenhagen last week.
But the Danish proposal had remained under wraps until The Guardian newspaper published it on its website during the second afternoon of the conference.
The documents show that at the broadest level, developed and developing worlds are split on several points:
the level of cuts from developed countries
the establishment of a target date by which global emissions should peak and begin to fall
most fundamentally, the shape of any future deal.
The BASIC draft sees emission reductions from developed countries coming under the Kyoto Protocol, whereas the Danish draft envisages all measures coming under a single new agreement.
Although this might appear a technical point, developing countries have so far remained adamant on the retention of the protocol because of the measures it contains on financial assistance and technology transfer, and because it is the only legally binding treaty in existence that makes countries reduce emissions.
The only formal texts in the UN process are the ones tabled by the Chairs of this Copenhagen conference at the behest of the parties
The Danish text sets out a vision of greenhouse gas emissions peaking globally by 2020, then declining.
It specifies a 50% emissions cut globally (from 1990 levels) by 2050. Most industrialised nations have already pledged an 80% cut in their own emissions.
According to some calculations, those figures, when combined with projected population growth in the developing world, mean that per-capita emissions in developing countries will remain below those in the west, "locking in" inequality.
Oxfam's Antonio Hill said industrialised nations had to offer bigger cuts than are currently on the table.
"The targets need to rise in ambition and in line with what the science says," he told BBC News.
"We think that at least 40% (from 1990 levels by 2020) is needed; and even that is not enough to produce equity."
However, Mr Hill suggested that measures on transferring finance from industrialised to developing countries - to help them curb their emissions and help them protect against the impacts of climate change - were "quite good".
Other observers, such as Sol Oyuela from the development agency CAFOD, were more damning.
"There is a UN legal process which is the official negotiating text; there is no need for any other texts.
"To be working on a rival text is a kick in the teeth to the UN process that has been negotiated for so long."
Yvo de Boer, executive secretary of the UN climate convention, also said the document had no formal weight within the negotiations.
"This was an informal paper ahead of the conference given to a number of people for the purposes of consultations," he said.
"The only formal texts in the UN process are the ones tabled by the Chairs of this Copenhagen conference at the behest of the parties."
The UK government dissociated itself from the text.
"At this stage in the negotiation there's inevitably all sorts of texts doing the rounds and more will no doubt appear over the next 10 days," said a spokesman for the Department for Energy and Climate Change (DECC).
"The UK is continuing to strive for the most ambitious deal possible, as the prime minister has made clear again today."
Gordon Brown declared earlier that he would favour the EU moving from its current 20% target to 30%, which governments have agreed to do if there is a global deal here.
Over the next few days, small island states, least developed countries, the African bloc and the overall G77/China grouping are expected to present their own texts.
The small island states are expected to demand a legally binding outcome from Copenhagen, which many insiders say is impossible.
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