UN negotiators agreed at climate talks Saturday to take stock in 2018 of country efforts to cut fossil fuel emissions as part of a pact -- rejected only by Washington -- to limit global warming. 

Closing two weeks of talks in Bonn, some 12 hours into extra time, envoys gave the green light in Bonn for what they termed the 2018 "Talanoa dialogue" to assess how much more needs to be done if the world is to meet warming limits detailed in the 2015 Paris Agreement.

The stocktake will happen in phases, starting in January 2018 and concluding in December at the next round of UN climate talks in Katowice, Poland.

"The dialogue will be structured around three general topics: Where are we? Where do we want to go? How do we get there?" said a document gavelled through by conference president Frank Bainimarama in the early morning hours, applauded by exhausted negotiators.

"The dialogue should not lead to discussions of a confrontational nature in which individual parties or groups of parties are singled out," it added.

To bolster the Paris pact, which seeks to hold average global warming under two degrees Celsius (3.6 degrees Fahrenheit), nations have submitted voluntary emissions-cutting commitments.

But scientists say current pledges place the world on course for warming of 3 C or more, and counsel an urgent upgrade.

The UN process will use the stocktake to determine the shortfall, so that steps can be taken to make up the difference.

The discussion will be informed by a special report of the UN's climate science panel next year on the feasibility of an aspirational 1.5 C warming limit, according to the decision.