This annual session had been planned as a procedural meeting, more than a substantive one. But the slow pace in the face of mounting evidence of climate change disappointed environmentalists and others.
"It is not enough what we reached in the conference," Germany's Environment Minister Sigmar Gabriel told reporters. "Urgent action is necessary."
He said heads of state must instill "a new political momentum" into climate diplomacy next year, when German Chancellor Angela Merkel, who views climate change as a priority, leads the G-8 group of industrial nations.
Under the key agreement here, future meetings would review the workings of the Kyoto Protocol by 2008 with an eye toward setting new quotas on carbon dioxide and other emissions after Kyoto expires in 2012. A final agreement isn't likely until 2009 at the earliest.
China, India and others have resisted efforts to begin early talks in which they and other poor but fast-developing nations might be pressured to accept mandatory cutbacks in greenhouse-gas emissions. The final decision assured them the immediate process would not seek to negotiate cutbacks by developing nations.
The 1997 Kyoto pact obliges 35 industrial nations to reduce emissions of greenhouse gases by 5 percent below 1990 levels by 2012. The United States rejects that accord, with President Bush contending it would damage the U.S. economy and should have given poorer countries obligations as well.
But developing countries will likely resist considering emissions reductions until they see acceptance of mandatory caps by the United States — a prospect some see as possible after Bush leaves office in 2009. Some Third World delegations had favored delaying the Kyoto review until as late as 2011.
In a separate set of less-formal talks, to be completed next year, the Kyoto member countries explored ways to bring the United States into a global emissions-reduction regime.
Scientists attribute at least some of the past century's one degree rise in global temperatures to the atmospheric accumulation of carbon dioxide and other heat-trapping gases, byproducts of power plants, automobiles and other fossil fuel-burning sources.
Continued temperature rises could seriously disrupt the climate, scientists say. The world is already seeing some impact, they say, in the melting of the Arctic and Greenland ice caps, the retreat of glaciers worldwide and the accelerating rise of sea levels, as oceans expand from warmth and melted-ice runoff.
Environmentalists have feared disputes over timetables might delay negotiations so long that the world would be left without emissions caps for some time after the Kyoto Protocol expires.
"We are not seeing the bold leadership required. Further delay is totally irresponsible," said Catherine Pearce of Friends of the Earth International.
But European Union officials said the 2008 target for the Kyoto review — a process that would assess the latest science and the size of necessary cutbacks — should ensure no gap would open up after 2012 in emissions cutbacks by the 35 industrial nations.
The 2008 target means the world is "well on our way to a new climate-change regime," EU spokeswoman Barbara Helfferich said.
Too long a delay would likely have left a gap between Kyoto's reductions and a new series of cutbacks, undermining the long-term credibility of the new, multibillion-dollar carbon market, operating since early 2005 within the 25-nation bloc.
The EU, in imposing quotas on emissions from power plants and other energy-intensive industries, established a trading system whereby companies that don't use their full emissions allowances can sell credits to others that need them.
A similar market has developed in emission-reduction projects in the developing world, not obligated to cut emissions under Kyoto, but able to sell such credits to countries that are.
Speaking with reporters, Kenyan environmentalist Sharon Looremetta dismissed the Nairobi meeting as a failure. "Most major issues have been shelved until next year," she said.
Her nomadic Maasai people have already been stricken by cattle-killing drought attributable to climate change, Looremetta said, but the countries emitting global-warming gases are doing too little to help.
"We don't drive 4x4 cars, we don't go on vacation by airplane, but we do suffer from climate change," she said.