The latest round of talks that concluded Friday showed that the 194 negotiating countries have failed to even define a common target or method for curbing greenhouse gases - just one example of the ongoing divide among rich and poor nations.
Talks began in 2007, with the aim of wrapping up a deal in Copenhagen last December. But that didn't happen, despite the presence of 120 heads of state or government. It ended instead with a three-page statement of intentions brokered by President Barack Obama.
Though less than expected, the Copenhagen Accord scored some breakthroughs. It boiled down the core elements of a deal to 12 carefully worded paragraphs, and it inscribed hard-fought compromises by the main protagonists, the U.S. and China.
Details were to be filled in by the next major conference in Cancun, Mexico, starting in November.
But the accord was never formally adopted. A handful of countries led by oil giant Saudi Arabia and U.S. nemesis Venezuela blocked the required consensus. The paper was merely "noted" by the conference, stripping it of any legal force.
Now, much of the Copenhagen deal has been thrown open again. After five days of talks in Bonn, rich and poor countries traded recriminations, and some positions are back to where they were a year ago.
Developing countries tried to weaken their Copenhagen commitments to rein in carbon emissions by saying their actions were voluntary while emissions targets for industrial countries are binding.
China balked at U.S. suggestions for monitoring Chinese domestic action, saying it would infringe on national sovereignty.
Countries most threatened by global warming - African states facing water shortages and island states whose coastlines are retreating under rising seas - say the $100 billion a year in climate aid by 2020 promised in Copenhagen is not enough.
The sought-after climate agreement is meant to succeed the 1997 Kyoto Protocol, which required 37 industrial countries to cut emissions 5 percent below 1990 levels by 2012. Kyoto said nothing about the rapidly growing emissions by developing countries, nor did it set targets for the post-2012 period.
No one expects an agreement to be completed in Cancun. Christiana Figueres, the top U.N. climate official, says the conference should agree on a series of practical steps that can take effect quickly - financial and technological help for poor countries - while a legal agreement can wait another year.
Nonetheless, negotiators continue to work on a draft text of an agreement. Each section is packed with wording still to be agreed and with competing proposals.
It begins on page one: A Shared Vision for Long-Term Cooperative Action.
A U.N. scientific panel said in 2007 that rich countries should slash emissions by 25-40 percent below the 1990 benchmark by 2020 to have any chance of avoiding the worst effects of global warming, but the negotiators cannot agree on a collective target. So after Copenhagen, each country submitted pledges of what it believed it could reasonably do on its own.
The U.N. climate secretariat said the pledges would bring those countries to 12-18 percent over the next decade. That could lead to runaway climate change, virtually ensuring that extreme events like Russia's current drought and the flooding in Pakistan will become more common.
Some developing countries say the whole approach is wrong. Rather than letting countries decide how much each can reduce its emissions, the atmosphere should be seen as "carbon space" to be divided up equitably.
The idea found its way at the Bonn talks into the "Shared Vision" draft.
Advocates cite a study published last year in Nature magazine saying that to limit temperature increases this century below 2 degrees Centigrade (3.8 F), the world has a "carbon budget" of 750 gigatons of emissions by mid-century. This budget should be allocated according to population, factoring in how much countries historically have drawn on their account.
Industrial countries have 16 percent of the world's population, but they "occupy" 74 percent of the carbon space, Bolivian delegate Pablo Solon said at a presentation for delegates. Rich countries already have filled the air with carbon, using up much of their budget.
"If you spend all your salary in the first week you won't have anything left," Solon told reporters.
Poor countries with huge populations say this method will let them build their economies and catch up. But rich countries dismiss the notion as unrealistic and designed to score points against the rich countries.
Chief U.S. delegate Jonathan Pershing called it "completely impractical." Artur Runge-Metzger, of the European Commission, said any discussion of historical responsibility is "a cul de sac. It leads nowhere."
Mexico's special climate ambassador Luis Alfonso de Alba said only a few countries are behind it. "The majority is talking about the transition toward a green economy, and that's more important politically and conceptually," he told The Associated Press.
Arthur Max has been covering climate issues since 1990