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Amid news of hurricanes and typhoons, of rising seas and a hotter planet, this week, in San Francisco, California, Governor Jerry Brown is presiding over a Global Climate Action Summit.
It's designed to bolster the Paris climate accord process, an agreement President Trump withdrew the U.S. from last year. A major concern of scientists is the stability of the Amazon, the world's largest rain forest, often called the lungs of the planet.
Tonight, with the support of the Pulitzer Center, and in collaboration with The Nation magazine and PRI's "The World," special correspondent Sam Eaton takes us to Maranhao State in Brazil to look at the fight to save this vital forest.
It's dusk on the eastern edge of the Amazon rain forest. This is a hot spot for illegal logging. And for these Guajira Indians, patrolling their ancestral lands, the day is far from.
The spotter sees an empty canoe on the riverbank. We pull up to next it and move quickly up a narrow path into the forest. Someone just passed here, the branches showing fresh cuts from a machete. And then, just ahead, we hear their voices coming down the path.
The Guajira Indians, armed and in full camouflage, crouch down for an ambush. Three boys from the settlement across the river, just outside the Caru indigenous territory, where the Guajira live, they confess to cutting trees in the Guajira's forest to make and sell charcoal, a valuable trade in this impoverished region of the Amazon.
They're taken back to the boat and then up the river to the Guajira's camp for questioning. These vigilante patrols began six years ago as a way to battle the region's powerful logging mafia. They call themselves the Guardians of the Forest. It's dangerous work.
The land they're protecting is part of a mosaic of indigenous territories that hold nearly all of the remaining forest in Maranhao State, one of the most violent and lawless regions in the world.
Claudio Da Silva, the leader of the Guardians, says he's received dozens of death threats.
Claudio Da Silva (through translator): This struggle for us is war, because it is dangerous, risky. The invaders don't respect us. They want confrontation. We run into armed hunters. The loggers carry arms. The farmers are armed. It's a war in which we can die at any time.
Brazil today is the deadliest country in the world for land defenders, a trend that's rising in recent years,with more than 140 killings since 2015, according to Global Witness.
Maranhao, where the Guajira live, is perhaps the most dangerous. From right here where I'm sitting in the middle of the Caru River, which marks the boundary between the indigenous reserve on one side and rural Brazil on the other, the difference between these two communities couldn't be more apparent.
You look right over the riverbank here and the forest is completely gone. The resources have been used up and taken away.
On this side, you have pristine forest. And so the tension between these two communities is constant.
Aside from the human toll, it's a war that's also causing untold damage to the world's climate.
Claudio Da Silva (through translator): This is something we would like the white people on the other side to understand, that what we are protecting here, this forest, isn't only for the Indians. It is for everyone. They would reap the benefits of having the forest preserved as well.
It's a message Da Silva wants spread more widely. In Brazil, deforestation is on the rise again, after years of declines. It jumped 29 percent in 2016 over the previous year, losing an area of forest the size of Yellowstone National Park.
It was also another grim milestone for the Amazon. For the first time, widespread drought and fire caused the forest to release more carbon into the atmosphere than it absorbed, endangering one of the planet's most powerful tools for buffering the effects of climate change.
The Amazon was buying you some time that it's not going to buy anymore.
That's research scientist Carlos Quesada, or Beto, as people here call him.
Deep in the Amazon forest, Quesada's team of scientists from Brazil's National Institute for Amazonian Research have been calculating, leaf by leaf, the forest's capacity to absorb CO2, a greenhouse gas that causes global warming on the one hand, but is also food for plants, fueling new tree growth through the process of photosynthesis.
And what they have found doesn't bode well for the planet.
Before, the Amazon forest as a whole was taking the emissions of all cars on the planet. And now it will stop. The effects of the increase in CO2 in the atmosphere are going to be much higher. And CO2 will grow in the atmosphere in a much, much higher rate.
Quesada says that change is happening even in the most pristine forests like this one. By burning fossil fuels, humans have pushed carbon dioxide concentrations in the atmosphere higher than they have been in more than 800,000 years.
These trees can no longer keep up.
So, we have already a fragile system that may be on the edge. And then you bring on fragmentation, deforestation, cattle ranching, illegal logging. All this pressure over the forest usually also brings on with fires.
So you imagine on top of this a future climate that is drier and hotter. So, this would really be a tipping point in the future of the Amazon.
A tipping point that could cause more than half of the Amazon forest to die back permanently, if deforestation continues at its current pace, a terrifying runaway climate change scenario laid out in the so-called Hothouse Earth paper, published last August in proceedings of the Natural Academy of Sciences.
Scientists say avoiding that outcome means growing more trees, not cutting them down. But in the halls of power in Brasilia, the dominant political coalition, which represents agribusiness and landed elites, is ignoring that warning.
They have introduced over a hundred bills to roll back environmental protections and reduce the land rights and autonomy of indigenous people.
Congressman Nilson Leitao heads the agribusiness lobby.
Nilson Leitao (through translator): I can say with certainty Brazil's debt with the Indians is not the land.
This view runs counter to multiple scientific studies that found the best way to defend forests is to empower the people who inhabit them, granting them land rights and legal standing.
But under Leitao's leadership, they're trying to expand mining and agriculture into the Amazon's indigenous lands.
Brazil's indigenous groups are fighting back. In April, more than 3,000 people from over 100 different tribes descended on the capital, Brasilia, for a week of protest.
Claudio Da Silva and the Caru Guardians also made the long journey. It was one of the largest mobilizations of indigenous people in Brazil's history.
Sonia Guajajara, a vice presidential candidate and head of the Articulation of Indigenous Peoples of Brazil, organized the mobilization.
Sonia Guajajara (through translator): We have always lived in a war in Brazil. The colonization period was marked by many deaths, murders and extermination of peoples, and this hasn't stopped. This war in Brazil is ongoing, and requires our constant resistance.
Back on at the Caru indigenous territory in Maranhao, Da Silva and his band of Guardians rise at dawn for another patrol. This time, the raid is a possible marijuana plantation. And because of the potential for a shoot-out with drug traffickers, a heavily armed military police unit comes along, in a rare show of support.
It turns out to be a cassava field, planted by land grabbers after clearing the trees for charcoal. The Guardians cut and burn the crops. But the forest will take decades to recover.
Raimunda Guajajar, one of the female guardians, or warriors, as they call themselves, says defending the forest is the Guajira's fate.
Raimunda Guajajar (through translator): If someday I die, there are my children, my grandchildren to keep going, to say, I will do the same work that my grandfather did, that my grandmother did, that my mother and my father did.
"We're not going to give up," she says. We will fight until we die.
For the "PBS NewsHour," I'm Sam Eaton, Maranhao, Brazil.
Special correspondent Sam Eaton reports with support from the Pulitzer Center, in collaboration with The Nation and PRI's The World.