PARIS - Investing billions today to protect threatened ecosystems and dwindling biodiversity would reap trillions in savings over the long haul, according to a UN-backed report issued Friday.

A coral reef Indonesia. Investing billions today to protect threatened ecosystems and dwindling biodiversity would reap trillions in savings over the long haul, according to a UN-backed report. (AFP/File/Romeo Gacad) More than a billion of Earth's poorest denizens depend directly on coral reefs, forests, mangroves, aquifers and other forms of "natural capital" to eke out a living.

Unless world leaders take swift action to halt the accelerating depletion of these resources, the result could be hunger, conflict and environment refugees, the study warned.

"Recognising and rewarding the value delivered to society by the natural environment must become a policy priority," said Pavan Sukhdev, who headed The Economics of Ecosystems and Biodiversity (TEEB) paper released in Brussels.

Governments have an economic interest in providing tax and other incentives to spur a switch from short-term profits through exploitation to long-term stewardship of natural resources, the report argued.

An annual investment of some 45 billion dollars in expanding protected areas -- on land and at sea -- would secure benefits of the order of four or five trillion dollars per year over a period of decades, said Sukhdev.

One case cited described the replanting last year of nearly 12,000 hectares (30,000 acres) of mangroves in southern Vietnam. The initiative cost about one million dollars, but will save annual expenditures on dyke maintenance of well over seven million dollars.

"Whereas climate change is a global issue with local ramifications, biodiversity is a collection of local issues," Sukhdev said in an interview with AFP.

Such examples could -- and should -- be multiplied thousands of times over, he said.

With less than a month before the Copenhagen climate summit tasked with forging a vital accord on climate change, carving out a major place in the deal for forests is cited as the most urgent of 10 recommendations.

Tropical forests in particular can play a double role in reducing the amount of heat-trapping greenhouse gases in the atmosphere.

"Deforestation accounts for 20 percent of greenhouse gas emissions," making it a critical target for emissions cuts, Sukhdev said.

"But forests are also today's biggest mitigation engine because they are capturing 15 percent of the total carbon dioxide we emit," he added.

Expanding that capacity to soak up dangerous CO2 should also be an integral part of any climate agreement, he argued.

After unsustainable use of land and oceans, climate change is the second major driver of biodiversity loss and the withering of so-called "ecosystem services" that humans wring from nature.

Earlier this year G20 nations vowed to keep global average temperatures from rising more than two degrees Celsius (3.6 degrees Fahrenheit) compared to pre-industrial times.

But for some ecosystems that may be too little too late.

Tropical coral reefs sustain half a billion people worldwide but are already in a downward spiral after an increase of less than 1.0 C (1.8 F), say marine biologists.

"Five hundred million people who will have to be looked after. What are you going to do if -- more likely 'when' -- that problem hits you?" asked Sukhdev.

Another priority should be scrapping subsidies that drive economic activity that damages the environment, the report said.

The most obvious target are those for fossil fuels. "Between price and production subsidies, there's something like 240-300 billion dollars worth every year," Sukhdev said.

The TEEB report, supported by the UN Environment Programme, was launched by the European Commission in 2007 after G8 and major emerging economies called for a global study on the economics of biodiversity.

The final synthesis report will be completed in October 2010.