An unidentified man sits next to a felled tree Dec. 13, 2007, at the Afi mountain forest reserve near Ikom, Nigeria. From Brazil to central Africa to once-lush islands in Asia's archipelagos, the world's rain forests are shrinking because of human encroachment.

Abo Ebam, Nigeria ? In the gloomy shade deep in Africa’s rain forest, the noontime silence was pierced by the whine of a far-off chain saw. It was the sound of destruction, echoed from wood to wood, continent to continent, in the tropical belt that circles the globe.

From Brazil to central Africa to once-lush islands in Asia’s archipelagos, human encroachment is shrinking the world’s rain forests.

The alarm was sounded decades ago by environmentalists – and was little heeded. The picture, meanwhile, has changed: Africa is now a leader in destructiveness. The numbers have changed: U.N. specialists estimate 60 acres of tropical forest are felled worldwide every minute, up from 50 a generation back. And the fears have changed.

Experts still warn of extinction of animal and plant life, of the loss of forest peoples’ livelihoods, of soil erosion and other damage. But scientists today worry urgently about something else: the fateful feedback link of trees and climate.

Global warming is expected to dry up and kill off vast tracts of rain forest, and dying forests will feed global warming.

“If we lose forests, we lose the fight against climate change,” declared more than 300 scientists, conservation groups, religious leaders and others in an appeal for action at December’s climate conference in Bali, Indonesia.

The burning or rotting of trees that comes with deforestation – at the hands of ranchers, farmers, timbermen – sends more heat-trapping carbon dioxide into the atmosphere than all the world’s planes, trains, trucks and automobiles. Forest destruction accounts for about 20 percent of manmade emissions, second only to burning of fossil fuels for electricity and heat. Conversely, healthy forests absorb carbon dioxide and store carbon.

“The stakes are so dire that if we don’t start turning this around in the next 10 years, the extinction crisis and the climate crisis will begin to spiral out of control,” said Roman Paul Czebiniak, a forest expert with Greenpeace International. “It’s a very big deal.”

The December U.N. session in Bali may have been a turning point, endorsing negotiations in which nations may fashion the first global financial plan for compensating developing countries for preserving their forests.

The latest data from the Food and Agriculture Organization (FAO) helped spur delegates to action.

“Deforestation continues at an alarming rate of about 13 million hectares (32 million acres) a year,” the U.N. body said in its latest “State of the World’s Forests” report.

Because northern forests remain essentially stable, that means 50,000 square miles of tropical forest are being cleared every 12 months – equivalent to one Mississippi or more than half a Britain. The lumber and fuelwood removed in the tropics alone would fill more than 1,000 Empire State Buildings, FAO figures show.

Although South America loses slightly more acreage than Africa, the rate of loss is higher here – almost 1 percent of African forests gone each year. In 2000-2005, the continent lost 10 million acres a year, including big chunks of forest in Sudan, Zambia and Tanzania, up from 9 million a decade earlier, the FAO reports.

“These forests are the greatest global public utility,” Britain’s conservationist Prince Charles said in the lead-up to Bali. “As a matter of urgency we have to find ways to make them more valuable alive than dead.”