MANAUS, Brazil – Julio Tota stood atop a 195-foot steel tower in the heart of the Amazon rain forest, watching “rivers of air” flowing over an unbroken green canopy that stretched as far as the eye could see.

These billows of fog showed researcher Tota how greenhouse gases emitted by decaying organic material on the forest floor don’t rise straight into the atmosphere, as scientists had supposed.

Instead, they hover and drift – confounding scientific efforts to unlock the secrets of the world’s largest remaining tropical wilderness.

“What we’ve learned is the Amazon rain forest is much more fragile and much more complex than we had first imagined,” Tota said. “My research is pretty specific. It’s aimed at showing why all our measurements are probably off.”

Tota is part of the Large Scale Biosphere-Atmosphere Experiment, a decade-old endeavor involving hundreds of scientists, led by Brazilians and with funding from NASA and the European Union. Their open-air “laboratories” are 15 such observation posts spread over an area of rain forest larger than Europe.

The project’s goal is to make the best scientific arguments for why this vast rain forest – along with other endangered forests in Africa, southeast Asia and elsewhere – is essential to combating global climate change.

But as the first phase of the $100 million experiment draws to a close, its researchers acknowledge that the data have raised more questions than answers.

Scientists can now say with certainty that the Amazon is neither the lungs of the Earth, nor the planet’s air conditioner. Paradoxically, the forest’s cooling vapors also trap heat, by reflecting it back toward Earth in much the same way greenhouse gases do.

But a key question remains unanswered: Does the Amazon work as a net carbon “sink,” absorbing carbon dioxide, or is it adding more CO2 to the atmosphere than it is subtracting, because of burning and other deforestation that have claimed an average 8,000 square miles – an area the size of Israel or New Jersey – each year of the past decade?

Some computer simulations suggest deforestation could cause droughts as far afield as the U.S. grain belt, apparently because chain reactions in the atmosphere would shift the Polar Jet Stream and the precipitation it brings.

These questions take on new urgency as global warming’s effects become ever more apparent, and as forests fall at a nonstop pace.

In one sign of growing concern, Brazil’s national leadership met in emergency session on Jan. 24 to deal with a sudden surge in deforestation after a three-year slowdown.

New studies suggest the Amazon may be approaching a tipping point, at which the drier conditions caused by deforestation will reduce rainfall enough to transform the humid tropical forest into a giant savanna.

“If you cut down all the tropical forests in the world, you may increase CO2 concentrations by 25 percent,” said Brazilian climatologist Carlos Alberto Nobre.

“It’s important to keep the forests intact because we are in a global warming crisis and it’s important not to reach a tipping point from which we can’t come back.”