Just one day is left in a key round of talks intended to propel 195 countries towards an historic accord in Paris just over six months from now.
But after 10 days' haggling, observers said almost nothing has been done to demine a text stuffed with political explosives.
"There has been too much time spent fiddling around with the unimportant details of the text," Christian Aid's Mohamed Adow said.
"Negotiators have acted like schoolchildren colouring in their homework timetable and not getting around to any actual homework."
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It would limit global warming to two degrees Celsius (3.6 degrees Fahrenheit) over pre-Industrial Revolution levels, fending off crippling droughts, floods, storms and rising seas.
But the draft agreement, sprawling over nearly 90 pages, reflects the position of every single country, with many views in direct contradiction to others.
The Bonn meeting has focused on maintaining consensus, by surgically removing duplicated text or finding laborious compromise on some of the less contentious wording.
The tough decisions will ultimately be made by ministers and heads of state, as negotiators have no mandate to make political concessions.
"We are gravely concerned about the progress of the negotiations and would like to express our utmost disillusionment on the mistrust reigning in the corridors," said Mithika Mwenda of the campaign group Pan African Climate Justice Alliance.
"We challenge the parties to effectively utilise the remaining few hours to agree on something concrete that will illuminate some hope to millions of people waiting for signals that this will cease to be an endless game of musical chairs."
One of the biggest is how to encourage countries to crank up their pledges of carbon cuts, and monitor that they honour their promises.