A forest once valued by what its trees fetch on the timber exchange might instead be valued according to the carbon dioxide it absorbs, the animals it supports, the water it filters and the firewood it provides. Or it could be revalued with future generations in mind. That might lead to higher felling fees, pricey replanting requirements or more expensive wood. Some might rethink the economic benefit of cutting it down. Science would become a more important factor in economic decision-making.
Some businesses, however, are embracing the idea to appeal to consumers demanding more accountability. Supermarkets like Britain's Tesco now offer carbon footprints on packaging alongside calorie counts.
At a national level, green accounting is already being embraced by some governments, even if still in piecemeal fashion.
India in April announced plans for green national accounts by 2015 though it's unclear if the country's chaotic bureaucracy can reach that target. Australia will soon begin taxing carbon dioxide emissions, which Costa Rica has been doing for a decade to fund forest preservation.
Late last century, a team of U.S., Dutch and Argentine researchers put a $33 trillion value a year on natural resources such as water, wood and fossil fuels and "services" such as a forest's absorption of carbon dioxide. The estimate is more than double the value of the U.S. economy, the world's largest. While admitting difficulties and uncertainties in their methods and calculations, the team's report said the $33 trillion figure was conservative.
Carbon credits, perhaps the best known example of giving a value to an environmental good, also illustrate the difficulties. Experts thought the pricing of carbon credits might have been straightforward, since emissions are easily measured and every CO2 unit is the same. But the carbon market wobbled wildly for years over estimates ranging from $5 to $500 per unit.
Other resources open worlds of debate. Water — frozen, liquid or gas, it's found just about everywhere from vast oceans or tropical mist to mountain glaciers and underground aquifers. It's used for drinking, bathing, growing plants, processing sewage, powering hydroelectric plants, driving weather systems and more. So not all water is created equal.
But should one lake be worth more than another? Does it matter if people depend on it, or if it supports schools of tasty fish? Should it even matter what it's used for now? Or is it more important to consider if it can be replenished?
Some argue such questions make it clear that subjecting the natural world to free market ideology is immoral and counterproductive.
"The result would be the further privatization of essential elements of our planet to which we all share rights and have responsibilities," writes Hannah Griffiths from the World Development Movement, a UK-based anti-poverty campaigning organization, in a recent essay for the Guardian.
Still some experts in the field say the world is on track to having comprehensive green accounts within 10 to 15 years.
A crucial advance has been the United Nations' quiet adoption in April of a framework of agreed concepts and definitions for green accounting that can be applied in any country. It took two decades to develop but stops short of valuing complex ecosystems.
"The accounting is not pie in the sky anymore," said economist Peter Bartelmus, who led the original U.N. effort.
The World Bank, meanwhile, is backing projects in Botswana, Colombia, Costa Rica, Madagascar and the Philippines that are looking for ways for national accounts to include the value of natural resources.
"Doing something is better than doing nothing. We shouldn't even aim for perfection, either," said Sen, the former statistician.
"It is much more important to come up with a methodology that people find intuitively acceptable rather than looking for hard commercial truths. If at a gut level people find it fair, then I think we can run with the idea."