The three-hour session ended early today, leaving top advisers to work out the final language before the summit of a draft agreement on how to tame global warming and help poor countries cope with its impacts.

‘‘The advisers will get back to work at three in the morning to craft a proposed political agreement that will be presented to heads of state at 8am,’’ a European diplomat said.

“Everybody present understood that there had to be a text,’’ said the source, who was present at the meeting.

‘‘The idea is to have a political accord as soon as possible, but it’s going to be tough,’’ he added.

The declaration will most likely call for preventing global temperatures from going up more than 2 Celsius degrees (3.6 Fahrenheit degrees) compared with pre-industrial times.

It will also tally up the pledges from rich nations on cutting greenhouse gases by 2020, and propose a target for all countries by mid-century.

If the declaration is accepted at the summit, negotiators will then transpose its objectives into the texts that have emerged from two-year UN negotiations under the UN Framework Convention on Climate Change (UNFCCC).

A document leaked from the UN secretariat says the world will warm by about 3 degrees Celsius this century if the greenhouse gas cuts being proposed at Copenhagen are followed through.

• Christopher Monckton of Brenchley writes from Copenhagen: The draft deal, pulled together at an all-night session here (which is part of the usual script for such conferences), was made possible by the promise of a huge injection of cash by the United States, which, however, cannot hand out the cash unless Congress approves it – which may not happen. The deal demands much, but methods of enforcement are few, despite an apparent concession by China, which had previously refused to endure international compliance inspections for any emissions reductions not paid for by the West. The UN had previously forecast only 3.4 C of warming, so the effect of the deal, even if it were implemented in full (which it won’t be), would be to prevent 0.4 C (less than 1 Fahrenheit degree) of “global warming”, and at vast cost. Never in the field of human politics has so little been achieved at so much cost to so many for so little benefit to so few.