LONDON The world relies on a range of services nature provides -- water filtration by forests, pollination by bees and a supply of wild plant genes for new food crops or medicines.
If nature charged for these, how much would it cost?
Most such values are excluded from measures of national economies and from prices and markets which would force businesses and governments to recognise them, and the result has been a bias towards development over conservation.
U.N. states have proposed a new body, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), to advise on valuing nature and conservation targets.
An early priority should be measurement, said Pavan Sukhdev, study leader for The Economics of Ecosystems and Biodiversity (TEEB) U.N. initiative, which published a business and biodiversity report this week.
"For a country to say 'let's increase biodiversity', it's quite difficult because it's not measuring biodiversity," Sukhdev said.
"That is a big challenge for the IPBES, to create a right set of metrics. The logical sequence is first establish what is biodiversity, what are you measuring, agree on it, so that countries are doing it pretty much the same way."
The U.N. General Assembly is expected officially to endorse IPBES later this year.
"It's bringing the world's best scientists together under an inter-governmental body, so governments can commission specific questions to that body, to provide them with guidance," said Achim Steiner, executive director of the United Nations Environment Programme.
In a further political step, on the agenda at a U.N. meeting in October in Japan is an "access and benefit-sharing" regime for countries which are home to plants and other species valued by agriculture or the pharmaceutical industry.
The idea is to give such countries a share of profits from product development.
"It has major implications for the economic benefit of conserving biodiversity," said Steiner.
Damage to natural capital including forests, wetlands and grasslands is valued at $2-4.5 trillion annually, U.N. reports estimate, a figure excluded from measures of the global economy, or GDP.
Of 48,000 species assessed for extinction risk as of 2009, some 2 percent were already extinct or extinct in the wild, says the International Union for Conservation of Nature (IUCN).
Part of the difficulty in recognising nature is the problem of assessing its various services using economic markets.
In the fight against climate change, a pure market approach has been devised to put a value on carbon-free air in the European Union's emissions trading scheme, by generating tradable carbon permits.
While some of nature's services could be similarly traded as commodities, such as proposed "rainforest bonds" which would pay for forests' wildlife, fresh water and carbon storage, most biodiversity cannot be valued or traded directly.
"We should probably be thinking about biodiversity less like the carbon market and more like a real estate market, these are very distinctive, unique assets, they can be graded and valued but they're not interchangeable," said Joshua Bishop, chief economist at the IUCN.
"It's not a commodity like carbon dioxide."
Less direct, private sector opportunities indirectly tied to conservation are booming, such as eco-tourism and organic food, UNEP argued this week in its business and biodiversity report.
And forest markets were still on track, said Sukhdev, pointing to a deal to raise about $4 billion to pay tropical forested countries not to chop their trees.
"It is complex but at the same time I think there is a huge willingness," said Sukhdev. "It will take time."