Though opinions were still poles asunder, participants at the Petersberg Climate Dialogue emerged from three days of discussion which ended Tuesday with guarded optimism.

They based their optimism on hopes of reviving stalled debate and rekindling practical cooperation among those who attended the United Nations climate change conference in Copenhagen last year.

The Petersberg dialogue was co-hosted by Germany and Mexico which is to host the follow-up to the Copenhagen conference in November.

"We succeeded in having a productive, trust-building platform," German Environment Minister Norbert Roettgen told reporters on Tuesday.

"We have made significant progress in three important fields of global climate change policy, that is, tropical forest protection, adaptation and green growth," he added.

The minister explained that France and Norway put forward an initiative on stopping deforestation while Germany pledged to provide developing countries with 350 million euros (465 million U.S. dollars) for forest protection in the next three years.

Roettgen said his country and South Africa offered a mitigation initiative aimed at "sharing our experience on sustainable development with developing countries."

But the German minister pinned sustainability on green growth. "What necessary framework is for green growth, what necessary tax incentives are to be in place, how emission trading systems work, we want to introduce German experiences on these issues," Roettgen said.

Also during the Petersberg dialogue, Spain, Costa Rica and the United States put forward an adaptation initiative for capacity building for the poorest nations in particular through financial and technological support, according to Roettgen.

Environment ministers from 43 countries agreed that concrete cooperation should be integrated into the ongoing negotiation process to provide insight on barriers and thus provide key lessons and real experience for inclusion in further negotiations.

"Talks on emissions trading were better than expected," Roettgen said. Though some countries still had reservations, there was an overall "great openness" for further discussion.

Five months after Copenhagen and seven months before Cancun, many environment officials and experts are still doubting whether the next UN meeting would be able to break the deadlock by inking a legally-binding global deal.

"It is extremely important that we have a set of concrete decisions coming out of Cancun, but we need to look at the process realistically," European Commissioner for Climate Action Connie Hedegaard told the press at Petersberg just outside Bonn.

Some experts say that though progress made at Petersberg was encouraging, it was confined to a rather limited range of issues whereas the most important questions were left unanswered.

Scientists argue that the current voluntary emissions cut pledges in Copenhagen Accord are expected to warm up Earth by 3.5 to 4.0 degrees Celsius, well over the 2-degree Celsius "red line" of danger.

The United States, one of the main emitter players in climate talks, remains uncertain about its targets and actions to cut emissions.

"The U.S. pledges in the Copenhagen Accord depend on national legislation, which is currently stalled in the Senate," said Martin Kaiser, climate policy director for Greenpeace International.

"So basically that means they have not pledged anything yet - that is the biggest problem we have."

Yvo de Boer, standing executive secretary of the UN Framework Convention on Climate Change, has said that he saw slim chances of reaching a strong enough agreement in Cancun because of the fact that the difficult situation since Copenhagen has not fundamentally changed.

But he expected that Cancun might yield some "substantial results" which would provide instruments for further negotiations and increase the level of ambition.

"I think it would be a great pity if this were the only opportunity of the minister's engagement (in climate talks) between now and Cancun," de Boer added, calling for continued involvement of environment officials from various countries.