The latest round of UN climate change talks closed last week with delegates divided on how much progress had been made.
The negotiations in Bonn were the latest in a series designed to culminate at a meeting in Copenhagen in December 2009 to agree a successor to the Kyoto Accord.
Critics warned that the Bonn talks, which assembled 2,000 delegates from 170 nations, were already behind schedule and the chances of a meaningful agreement before the end of next year were receding.
WWF's climate policy co-ordinator Kathrin Gutmann said progress in Bonn had been " feeble".
She added that too many countries had come to the talks with "shopping lists " rather than effective blueprints for how to move to a lower-carbon economy.
Several delegates at the talks echoed her comments.
Norwegian official Harald Dovland said the negoations had been "slow and difficult". He added that without a "completely new spirit of co-operation" there was a genuine fear that the talks would fail.
And India's Chandrashekhar Dasgupta said there had been too much "beating about the bush", with rich nations notable for their "deafening silence" on how they would deliver cuts in emissions.
Although the UN's top climate change official, Yvo de Boer, admitted that the task of delivering an agreement remained "daunting", he insisted there was still cause for optimism. He said talks on how to help developing countries adapt to climate change had made good progress.
Luiz Figueiredo Machado, chair of the ad hoc working group on long-term co-operative action under the convention, agreed but warned that the negotiations would have to accelerate at the next round of talks in Ghana in August.
"Parties have made the all-important transition from discussions and are entering the negotiating phase," he said. "But what is required are more targeted proposals in the next sessions."
