A day after negotiations threatened to collapse, delegates adopted a modified text in Warsaw that both developed and developing countries said they could live with.
"Just in the nick of time, the negotiators in Warsaw delivered enough to keep the process moving," said climate analyst Jennifer Morgan of the World Resources Institute.
Rich and poor nations have been at loggerheads ever since the talks opened on November 11 over who should do what to curb the march of planet warming.
In particular, they clashed over sharing responsibility for curbing climate-altering greenhouse gas emissions, and about funding for vulnerable countries.
By Friday afternoon, the talks had seemed on the brink of collapse and observers warned of an impending deadlock as sleep-deprived negotiators just could not see eye to eye.
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The belligerent negotiations, gathering more than 190 countries, were to have closed at 1700 GMT on Friday.
Twenty-four hours later, exhausted and stubble-bearded delegates applauded as their text, providing an outline for the road to a 2015 deal, was finally passed after an hour-long emergency huddle in the Warsaw National Stadium hosting the UN parley.
Notably, negotiators replaced the word "commitments" for nationally-determined emissions cuts, with "contributions".
Emerging economies like China and India had objected to any reference to "commitments" that would be equally binding to rich and poor states and did not take into account historical greenhouse gas emissions.
The issue is a fundamental one that has bedevilled the UN climate process since its inception 18 years ago.
Developing nations, their growth largely powered by fossil fuel combustion, blame the West's long emissions history for the peril facing the planet, and insist their wealthier counterparts carry a larger responsibility to fix the problem.
The West, though, insists emerging economies must do their fair share, given that China is now the world's biggest emitter of CO2, with India in fourth place after the United States and Europe.
The 2015 deal will be the first to bind all the world's nations to curbing atmosphere-polluting greenhouse gas emissions from burning coal, oil and gas.
The aim is to limit average global warming to 2.0 degrees Celsius over pre-Industrial Revolution levels.
On current emissions trends, scientists warn the Earth could face warming of 4.0C or higher - a recipe for catastrophic storms, droughts, floods and land-gobbling sea-level rise that would hit poor countries disproportionately hard.
The new pact, to be inked in Paris, will enter into effect in 2020.
