The Amazon is the world's largest rain forest, and it plays a vital role in the global climate. But 17% of it has been razed in recent decades. Trees give way to cattle ranches, soybean farms and subsistence agriculture. Worldwide, 1.2 billion impoverished people live off forests. If the rest of the Amazon were burned and cleared, it would emit 50 times more planet-heating gases than the annual output of United States.
Now, 190 countries are negotiating a new global climate treaty. To succeed, they must curb the slashing and burning of forests.
Tropical nations are starting to measure the carbon in their trees. Carbon credits can then trade on a global market, earning money to protect forests. Brazil's Juma reserve is one of several dozen forest carbon projects around the world.