The same thing that threatens the Indians threatens all of us. If the Amazon goes away, it will put the process of global warming (which scientists say is already creating stronger storms, heat waves and droughts) on steroids.
In his own way, one of the Enawene Nawe elders, a man named Kawaree, seems to understand this.
"If our land is destroyed," he tells us, pointing at me and my team, "we will die ... and you will die. .. and you will die. The only difference is you don't know it."
The Enawene Nawe are keenly aware of horror stories involving tribes in other parts of the jungle.
In fact, Survival International tells us about a tribe, called the Akunste, that is now down to its final six members.
We travel deeper into the Amazon to see for ourselves.
The Akuntsu live on a protected patch of jungle, completely surrounded by cattle ranchers. There's an outpost of government officials who live nearby full time, to protect the Indians.
One of these government officials takes us down the jungle path, past the Entry Prohibited signs, to the Akuntse village.
After an hour's walk, we see them. The final six.
They are incredibly friendly, embracing us and staring into our eyes. They ask me if I'm a doctor or a shaman.
There are four women left. Many of them are getting on in age. Genetically, it is virtually impossible for the Akuntse to survive. These six are all that's left of what was once a civilization with its own religion, culture and language.
Virtually no one outside the tribe speaks their language. The government official with us is actually the one who made first contact with this tribe in the mid-1990s. (He later shows us video of the encounter. The tribe members are so scared some of them are literally shaking.) From what he can piece together, ranchers massacred the tribe for their land. (The bullet wounds in the men corroborate that story.) Since no bodies have ever been found, no charges have been brought.
One of the men tells us he saw his parents shot before his eyes.
Another tells us he wants revenge on the whites who destroyed his tribe.
As the final members of the Akuntsu take us into their hut, the eldest male plays us a mournful song on his homemade flute. I realize that this is perhaps his most eloquent means of telling his story, and that what we're watching is a real-time human extinction.