The US may not be in a position to pledge anything at all, with domestic legislation yet to pass through the Senate.
The EU said last week it would contribute its "fair share" of the $100bn euros ($148bn; £90bn) per year that it calculates the developing world will need by 2020 in order to curb their emissions and protect their societies and economies from climate impacts.
But it stopped short of naming an exact figure for its contribution.
Studies by UN agencies suggest more than that is needed, and that funding on this scale should begin next year, rather than in 10 years' time.
A number of developing countries, notably Indonesia, have recently pledged to reduce the rate at which their emissions will rise; but the biggest of all - China - has yet to announce by how much.
Even the legal form of a new treaty remains to be decided, with a number of developing countries insisting that it must be an extension to the Kyoto Protocol, and industrialised governments equally insistant that it must be a completely new agreement - not least because the US Senate will not ratify the Kyoto Protocol.
Negotiators will begin work with a set of "non-papers" - elements of a possible treaty that do not carry the weight of a formal draft.
The chairman of the main set of talks, Michael Zammit Cutajar, has advised negotiators to concentrate on the "critical issues... that are central to the task", with details that could bog the discussions down left to one side.
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