As the heavens open, the canopy offers scant protection from the downpour, so the orangutans tear leaves off the trees to make pathetic little umbrellas to hold over their heads. It is an endearingly human gesture but, as a means of keeping dry, almost entirely futile. And it is not just the rain that makes these creatures seem so helpless. The relentless destruction of their tropical-forest habitat has endangered their entire species.

In Borneo, in the Indonesian province of Central Kalimantan, they can relax in a camp devoted to their welfare on the edge of the Tanjung Puting national park. But the park — 415,000 hectares of protected tropical heath forest and peat forest — is surrounded by oil-palm plantations.

These orangutans are refugees from forests cleared to make way for the plantations. Much as people like the creatures, and devotedly as conservationists work, the park is not enough to stem their remorseless decline. There is too much money in palm oil, as well as timber, coal, gold, zircon and the forest's other vegetable and mineral riches.

Yet prospects for the orang-utans have recently looked up. Climate-change fears have drawn attention to the work forests do to sustain not just wildlife but the planet itself. The outlines of a scheme under which developing countries would be paid not to cut down trees has been agreed.

Indonesia, for example, chafes at its reputation as the world's third-biggest emitter of carbon (a ranking it disputes). It has promised to cut its emissions by 26 per cent by 2020 or, if promised foreign cash actually materialises, by 41 per cent. It will achieve this in large measure by reducing deforestation.

However, turning the scheme — known as Reducing Emissions from Deforestation and Forest Degradation (REDD) — into actual conservation is not proving easy, either in Indonesia as a whole or in Tanjung Puting in particular. Next to the park is a stretch of peat-swamp forest, mostly degraded but rich in carbon. A Hong Kong firm called infiniteEARTH has earmarked this for a REDD project called Rimba Raya (infinite forest).

Showing promise

Biruté Galdikas, a renowned primatologist who has been studying orangutans in Tanjung Puting since 1971, is "thrilled" by the idea. Rescued orangutans, of whom more than 300 are in her care centre in the park, could be freed without danger to the wild population.

Rimba Raya seems to offer many other benefits. Trees would be replanted or conserved (Borneo's forest has more tree species per hectare than anywhere else); the forest would regenerate; some 10,000 people would benefit from ‘community development' projects such as one to increase fishing yields.

And the earth would be spared a huge amount of emitted carbon: by one calculation, as much as 75 million tonnes over the next 30 years. The project's investors, including Gazprom, a Russian energy giant that has paid in advance for some carbon credits, think it will be lucrative. And it has passed most of a tough certification process.

Yet Galdikas is worried that the project may never happen. Three years on, the final land-use decree has yet to appear. The problem is one that will dog REDD. To win certification, Rimba Raya has to show that the forest is under genuine threat: no point in giving carbon credits for conserving trees and peatland that were not in danger anyway.

This is a political battle that also reflects a broader struggle over REDD in Indonesia being fought at the national level. Last May Indonesia's president, Susilo Bambang Yudhoyono, announced a two-year moratorium on commercial deforestation starting on January 1 this year. In return, Norway committed $1 billion for REDD payments, but the moratorium has been delayed.

Much hope is invested in Kuntoro Mangkusubroto, head of Yudhoyono's ‘delivery unit', who is entrusted with implementing REDD, and the Norwegians.

But success will depend on the political will of the president. Erik Solheim, Norway's minister in charge of the environment and development, points to the encouraging example of Brazil, which has cut deforestation rates by 70 per cent in five years. Indonesia, he concedes, "is harder".

Galdikas knows what he means. "They all talk a wonderful talk," she says, "but the forest keeps getting destroyed."