The 12-day meeting of the UN Framework Convention on Climate Change (UNFCCC) set 2008 for launching a review of commitments under the Kyoto Protocol in order to accelerate cuts in carbon pollution after the pact's current pledges run out in 2012.

The so-called second commitment period runs from 2013 to 2017, and experts say it must deliver far deeper cuts in greenhouse gases to avoid wreaking havoc on the Earth's climate system.

But the Nairobi gathering did not set a deadline for concluding these negotiations, nor set down any conditions for the agenda. And decisions on outstanding technical questions that are important for activating some of Kyoto's existing mechanisms were postponed until 2007.

Environment ministers from industrialised countries also agreed that global emissions of greenhouse gases had to be halved, although they did not set a date.

The European Union has been pushing for a deadline of 2050, contending this will limit the rise in Earth's atmospheric temperature to 2.0 C (3.6 F) by 2100 compared with 1900.

"Thanks to the leadership of the European Union, we now have a solid work plan to combat emissions after 2012," said European Environment Commissioner Stavros Dimas.

"There is no time to wait. We must cut emissions by 50 percent in the next half a century to end global warming."

Greenpeace's Steve Sawyer welcomed the 50-percent target but lamented that no end date had been set for concluding the 2013-2017 negotiations, warning that any delay in implementing the second commitment round would rattle Kyoto's carbon market.

"Much more must be done to fill the gap between the stark reality of climate change and the slow incremental progress of these talks," said Sawyer, the group's climate policy advisor.

The failure to establish a timetable for the 2013-2017 negotiations is a "regrettable failure of political will," said a British development agency, Tearfund.

The meeting -- officially called a Conference of the Parties (COP) of the UNFCCC -- also ran into fire from grass-roots advocates for developing countries.

They said it threw up negligible gains for Africa, the world's poorest continent and the one that is the most vulnerable to climate change.

"The final declaration from Nairobi leaves millions of the poorest and most vulnerable people in limbo and is a frighteningly timid response to a significant global problem," said Andrew Pendleton, climate advisor to the British group Christian Aid.

"This was meant to be an African COP. It turned out to be a safari COP," said Sharon Looremetta, of Kenya's Maasai ethnic group. "Climate change tourists -- this is what I call you!"

UNFCCC Executive Secretary Yvo de Boer contended, though, that developing countries would "walk away with a very significant package."

He pointed to decisions on managing and financing Kyoto's Adaptation Fund to help poor countries cope with the effects of climate change and on setting a five-year work programme to identify which kind of adaptation measures would be useful.

Another area of progress was on streamlining the Protocol's Clean Development Mechanism (CDM), an incentive for transferring clean technology to poor countries, so that African economies could benefit from it, said de Boer.

Antonio Hill of Oxfam said the conference should have made financial pledges to the Adaptation Fund, which at present has only three million dollars in its coffers.

"This urgently needs to be turned into a multi-billion dollar fund if poor countries are to be helped in adapting to climate change," he said.

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