Key Takeaways from Episode 5 of Rewilding Amazonia

• The Amazon makes its own rain. During the dry season, the Amazon transpires more water than during the wet season—four to four and a half liters per square meter per day. Deep-rooted trees pull moisture from up to twelve meters underground and release it into the atmosphere, essentially manufacturing rainfall. The forest isn’t waiting for rain. It’s generating it.
• Flying rivers are real, and they affect you. About 40–50% of the moisture the Amazon produces doesn’t fall back where it rose. It gets carried south by wind currents—what Carlos Nobre named “flying rivers”—delivering rainfall to the Pantanal, southern Brazil, Argentina, and Paraguay. São Paulo, a city of twenty-two million people, gets a significant portion of its rainfall from a forest it can’t see.
• The tipping point has a number. If deforestation exceeds 20-25% of the Amazon—combined with global warming exceeding 1.5 degrees Celsius—the system tips irreversibly.
• River dolphins are diagnostic tools. Jimena Valderrama’s health assessments of Amazon river dolphins have found mercury levels seventy times the permitted limit, antibiotic-resistant bacteria, and parasites potentially crossing from cattle into wild dolphins for the first time. What’s in the dolphin is in the river, and in the people who eat from it.
• There is a boiling river in the Amazon—and science didn’t know it existed. Running at up to 87 degrees Celsius, 700 kilometers from the nearest active volcano, the Boiling River is the hottest naturally occurring micro-ecosystem in the Amazon. It is a living laboratory previewing what a post-climate-change Amazon might look like, and it sits at the intersection of the world’s greatest biodiversity and an extreme geothermal ecosystem we’ve barely begun to study.
• The window is still open. The tipping point is not inevitable. Near-zero deforestation, dramatic emissions reductions, and active restoration could still pull the Amazon back from the edge. The dolphins are still there. The jungle can still grow back. As Andres Ruzo puts it: charge the windmill.

The Living Network

Carlos: “If the deforestation of the Amazon becomes gigantic, the forest will not recover in more than 50% of the Amazon because you are going to change completely the climate in most of the southern Amazon. The dry season would become six months. The forest cannot regrow.”

That’s Dr. Carlos Nobre, one of Brazil’s most distinguished climate researchers, and the scientist who coined the concept of the Amazon’s tipping point. He first ran those numbers back in 1988, and spent the next several decades hoping he’d gotten it wrong. He hadn’t.

The more I learned about this place, the more I realized that the Amazon is more complex than I ever imagined—multiple systems operating together, each one dependent on the others and breathtaking in their own right. The atmosphere above, where invisible rivers of moisture move across a continent. The water at the surface, carrying up to 20% of the world’s riverine freshwater through some of the most biodiverse ecosystems on Earth. And beneath it all—an underworld of geothermal aquifers and subsurface systems that science is only beginning to map.

Together, they’ve taken forty million years to build. And right now, they’re all under pressure.

This episode travels through all three layers because the more we understand how these systems talk to each other, the clearer the stakes become when they start to break down, and why we need to protect them while we still can.

Welcome to Episode 5 of Rewilding Amazonia. I’m Brooke Mitchell.

Let’s begin in the rainforest’s clouds. 

Amazon Climate Science: Dr. Carlos Nobre

The Engine

To understand how the tipping point works—and how close we actually are—you first need to understand what the Amazon does as a climate system. And that story starts not with deforestation, but with geology.

The Andes didn’t just create a mountain range—they transformed the Amazon’s destiny. Before their uplift, much of the rainforest was concentrated closer to the equator, more limited in scale. But as the mountains rose over millions of years, they reshaped atmospheric circulation across South America, creating powerful rainfall systems that expanded precipitation deeper into the continent and helped transform the Amazon into the vast forest system we know today.

Carlos: “The Amazon has an average six hundred to seven hundred trees per hectare, and one fourth of the trees have very deep roots. The rooting system goes to seven to ten, twelve meters. During the dry season, the Amazon transpires more water than during the wet season—four to four and a half liters per square meter per day. The forest recycled water so well that about 45%—many studies show between 40 and 50%—is exported out of the Amazon to the south.”

During the driest months of the year, when it hasn’t rained in weeks, the Amazon is pumping more water into the atmosphere than during the wet season. The deep-rooted trees are pulling moisture from far underground and releasing it into the air, essentially manufacturing the rainfall that keeps the forest alive. And that moisture travels far beyond the forest itself.

Flying Rivers

Carlos: “We gave the name Flying Rivers to this water vapor. In the US it’s called Aerial Rivers, but we decided to call Flying Rivers. This water vapor is what really induces a lot of rainfall south of the Amazon — the tropical savanna, the Pantanal. About 50% of the rainfall in the Pantanal comes from the Amazon. Also, rainfall in southern Brazil, Argentina, Paraguay — 15% of rainfall in São Paulo depends on this water vapor.”

Flying rivers. Invisible currents of moisture carrying water from the Amazon forest to cities and farms thousands of kilometers away. São Paulo—a city of twenty-two million people—gets a significant portion of its rainfall from a forest it can’t see. The farmers of Argentina’s agricultural heartland depend on moisture that began its journey in the canopy of the Peruvian Amazon.

Water is only one part of what this system holds. Over tens of millions of years, the Amazon has accumulated more than 150 billion tons of carbon — stored in trunks, root systems, and soil — making it one of the planet’s largest terrestrial carbon stores. Release that carbon into the atmosphere, and the consequences ripple across every climate system on Earth.

The Tipping Point

In 1988, a different question started to consume Carlos. Not what does the Amazon do, but what happens if we push it too far?

Carlos: “I decided to ask a scientific question — well, you know, if the deforestation of the Amazon becomes gigantic, what’s going to happen? My study showed: if that happens, then the forest will not recover in more than 50% of the Amazon, because you are going to change completely the climate in most of the southern Amazon. The dry season would become six months. That’s the climate system for the tropical savanna. There will be no way — reduction of rainfall — the forest cannot regrow.”

His decades of subsequent research led to a clear threshold: if deforestation exceeds 20% of the Amazon, combined with global warming exceeding 1.5 degrees, the system tips. Long-term atmospheric monitoring towers planted across the Amazon—part of a massive experiment Carlos helped launch in 1999—are now measuring it in real time. The southern Amazon’s dry season has already lengthened by four to five weeks over the past 45 years. Rainfall is declining. Trees are dying at higher rates.

Carlos: “In the 1990s, the Amazon was removing more than 1.5 billion tons of carbon dioxide from the atmosphere. Now it’s removing much less, 300 million. And that area—the forest degradation, the dry season becoming warmer, drier, longer—the forest has become a carbon source.”

In its most deforested regions, particularly the eastern and southeastern Amazon, the forest has already crossed that line, shifting from carbon sink to carbon source. And Carlos is unambiguous about what happens to the rest of it if we don’t change course.

Carlos: “Even if we really don’t reduce emissions — and if we fail in completely getting to zero deforestation — we are going to reach a tipping point in the Amazon by 2040, but no longer than 2050. If we cross the tipping point of the Amazon, then by 2070 to 2100 we are going to lose about 70% of the Amazon Forest. We are going to release up to 2100 more than 250 billion tons of carbon dioxide. We’re going to lose the largest biodiversity. We are going to reduce a lot of the transport of water to the south — the flying rivers. The Pantanal will disappear. This is an ecoside. An ecological suicide.”

An ecological suicide. Carlos isn’t describing something happening to the Amazon from the outside — he’s describing a system that, pushed past a certain point, begins to dismantle itself. The tipping point is not inevitable, though. The pathway out exists: near-zero deforestation, a dramatic reduction in global emissions, and active restoration. The window is narrow and closing, but we haven’t crossed it yet.

Dolphins & Rivers: Jimena Valderrama

The Living Ambassador

The Amazon basin carries roughly 15–20% of the world’s riverine freshwater discharge, connecting ecosystems and communities across an area so vast that managing it requires international coordination on a massive scale. And unlike the atmosphere above, or the geology below, this water world has a living ambassador.

Jimena: “They are dolphins — for me, are like a Pokemon, or like a unicorn — are so, so incredible to exist, because they are pink and are in the middle of the river, and you can see the forest in the landscape. They are so strong animals, so resilient. They start to be in a freshwater ecosystem like five million years ago — they adapt themselves and evolved with this fresh water ecosystem.”

Five million years. While the Amazon was being shaped by the forces Carlos described, these animals were evolving alongside the river system and developing adaptations that exist nowhere else in the dolphin family.

Jimena: “They develop some things — they increase the size of their melon, to echolocate better, because in the Amazon you can see nothing in the water. So the echolocation is so much better than the other species of dolphins, because they need to see where is the fish, where is the trees in the water, where is the boats. They have like a radar in their mind. And they can move their head — the river dolphins can move this because they need to navigate inside the flooded forest. The water can change its level more than twenty meters. So the ecosystem is changing all the time and they need to adapt to this change.”

A landscape that completely transforms twice a year—from open beach to fully submerged forest and back again—and these dolphins have spent five million years learning to navigate both versions. Their bodies are an archive of everything this river system has ever demanded of them.

The Mirror

Through a health assessment program running across Brazil and Colombia, Jimena’s team captures individual dolphins for no more than twenty minutes, takes blood and tissue samples, runs ultrasounds, tests for parasites and infectious disease, and returns them to the river. What the data is showing is that the river is sick.

Jimena: “The dolphins are like a mirror of what happened around them. So if we have found high levels of mercury, that means the people who eat the same fish as the dolphins have high levels of mercury. If we found some antimicrobial resistance, that means the people around these dolphins don’t use antibiotics correctly, and they are in the river. They are a mirror of what happened. We try to use these dolphins to work with public health, with different governments, with different institutions — to show what happened in the river. And not just protect the dolphins, not just protect the river — but protect the people who depend on that.”

The health assessments are more than a conservation tool. They’re a diagnostic report on everything the river touches: the fish, the communities, the water itself. And the reports coming back are deeply troubling.

Jimena: “The red flag, the bigger red flag, is the mercury contamination. This is a very toxic element for the body — it accumulates and biomagnifies in the ecosystem. It’s like a silent enemy, because you eat mercury and don’t show signs in this moment. The mercury accumulates, accumulates, accumulates — and years later it can show what is happening. We found in different dolphins levels of over thirty-five milligrams per kilogram of mercury. And the limit permitted is 0.5 milligrams per kilogram. If this happened with the dolphins, it’s happened with the people.”

Seventy times the permitted limit. In animals sharing their food source with the communities living along these rivers. The source isn’t a mystery. Illegal gold mining releases mercury directly into river systems, where it enters the food chain and works its way up. The same criminal economy running through almost every crisis in this series is poisoning the water at its source.

Jimena: “We found two different antimicrobial resistances — we found Klebsiella, we found E. coli — different bacteria with a lot of resistance to normal antibiotics. That means the people around don’t use these antibiotics correctly. In Colombia, a lot of people can buy antibiotics without a prescription — so it’s so easy to find antibiotics and use them how they want. And that is what happened in the river.”

Beyond the antibiotic-resistant bacteria, Jimena’s team has found evidence of a parasite causing large papillomas in the reproductive systems of female dolphins, a parasite they believe may be crossing from domestic cattle into wild dolphins for the first time.

The Political Wins

In 2023, eleven of the fourteen countries where river dolphins are found signed a declaration committing to their conservation, including China, where related freshwater dolphin species live. That same year, the Ramsar Convention passed a resolution formally recognizing river dolphins as sentinels of aquatic ecosystems.

Jimena: “We achieved a resolution for river dolphins as sentinels of the aquatic systems in Ramsar sites. This is so important because the river dolphins are not in all the Ramsar sites — but it’s like an image, like an umbrella, like a sentinel of the aquatic ecosystem. It can show the importance of using one species to conserve the different Ramsar sites. It’s incredible.”

Jimena: “The first image that comes to my mind is the dolphin. You see the dolphin and it’s still there—still being strong, still being resilient, with all of the threats around them, but still there. They give me hope. They give me purpose to still do this. And the people who start to work with us—who change their mind, even a little bit, and start to have a different approach to the dolphins, to the process, to the environmental things—that gives me hope. And the children. When we have workshops in schools, talking about conservation, and you look at the eyes of the children—with all of the hope—that gives me hope.”

The Deep: Andres Ruzo

The Third Layer

Andres: “When I think of the Amazon, I ultimately think of the greatest celebration of life on our planet. This is one of the most interconnected systems anywhere, and it is absolutely wild how every detail just magically, beautifully interconnects. So when we’re talking about the Amazon, what we’re talking about is the Amazon basin, this is a water biome. This is the kingdom of water. But it also has a component in the air — people have talked about the flying rivers, the river system floating through the air that creates the rains. And then there’s another side, under the surface—the aquifers, the geothermal aquifers—and all of those three worlds come together. They interplay, they interact with each other. And that is the real basis of anything you want to study in the Amazon.”

Andres has spent years trying to understand how these layers connect. The tool he uses is water itself—specifically, the chemical fingerprints carried inside individual water molecules that reveal where they’ve been, what systems they’ve passed through, and how the surface world and the deep earth are talking to each other. The Amazon is not a forest sitting on top of geology. It is a conversation between three systems that has been running for millions of years.

The Legend

Andres: “My grandfather used to tell me this crazy story about the Spanish conquest of Peru — one of the details included a river that boiled. The legend of Paititi — El Dorado in Spanish — is a lost city of gold hidden deep in the Amazon. The Spaniards and the Inca had been fighting for forty years, the Inca are finally conquered, and new waves of conquistadors come into Peru looking for gold and glory. The Inca, out of vengeance, tell them — go to the Amazon, to the east, in the land of the plant, there’s an entire city made entirely of gold. And the few that return come back with horrifying stories: giant spiders that eat birds, snakes that could swallow a man whole, fierce warriors, powerful shamans. And one of the details was of a river that boiled.”

The story stayed with him. Years later, while mapping Peru’s geothermal energy potential for his PhD, Andres came across data points in the Amazon that made him wonder if the legend could be real. Every scientist he asked told him no. One senior geologist told him flatly not to ask stupid questions. Then he mentioned it to his aunt at a family dinner in Lima.

Andres: “She looks at me and just says — the boiling river does exist. It’s real. I’ve been there. And I’m looking at her like, you’re crazy. She says, I swam in that river. And I’m like, yeah, no, I definitely know you’re crazy. You swam in a boiling river? And she’s not messing with me — she used to do indigenous rights work, had made friends with the wife of the powerful shaman who protected the area, and they’d been invited to visit.”

For months, Andres and his aunt tried to reach the shaman. Eventually, his aunt made the call: they needed to stop waiting and just go. The next morning, they were on a plane at 5am—one hour to Pucallpa in the central Amazon, three hours by truck, an hour by motorized canoe, then another hour on foot through the jungle.

The Discovery

Andres: “I get to the top of this big hill, hot day, carrying the packs. We sit down for a break. In the background I remember hearing this sound — like an ocean wave constantly crashing. I asked the shaman’s apprentice, what is that? And he just kind of smiles and points down towards the valley below and he says — that’s the river. I look down and I see between the trees these wisps of what I thought was smoke. He says, go. So I bolt down this hill, run through this community, and suddenly I stop at the clearing — and I’m face to face with everything my aunt said was going to be there. Sixty-foot walls of green. A river flanked by ivory-colored stones. The water itself almost transparent turquoise. A thin layer of mist dancing in the breeze. As wide as a two-lane road, going on for at least 200 meters. And all I could think of was — that’s a lot of steam.”

Andres: “I run down to the edge. I take that first breath in — hot, thick, moist air going into your nose, down your throat, into your lungs — I wasn’t prepared for that. Like walking into a sauna without thinking twice. And then I take the temperature measurement. Eighty-seven degrees Celsius. One hundred and eighty-nine degrees Fahrenheit. Over 700 kilometers from the nearest active volcanic center.”

Water burns human skin at forty-seven degrees Celsius. This river was running at nearly twice that — and science had no record of it.

The Shaman’s Charge

Andres: “His response was — yes, of course, I give you my blessing to study this river, but I ask you, in turn, to help us bring it to the world responsibly. And no longer conceal to protect. And even then, he was painfully aware that not only was his culture facing cultural degradation — globalization is advancing — but also the jungle is disappearing and continues to disappear. I have dedicated, at this point, a third of my adult life, if not more, to this project from that moment on. And we continue fighting for it. I’m not going to stop until it’s protected.”

The shaman passed away recently. Andres carries that charge forward. Today the Boiling River has nearly 200 collaborators working on it from research institutions around the world.

A Living Laboratory

Andres: “This is the hottest naturally occurring micro-ecosystem in all of the Amazon. It is a perfect window as to what a post-climate-change-impacted Amazonia might look like — because depending on where you are in the boiling river’s valley, the subsurface temperatures might be ten degrees Celsius hotter than background temperatures. And it’s already hit steady state, and it’s already jungle. So how is that impacting plants? There’s a group looking at ants and insects. Fish specialists, bird specialists — all sorts of people trying to understand this area. We need to understand the baseline, so we can make sure we keep to it as much as possible in the face of human impact.”

Andres: “People don’t realize it, but all of modern biotech — all of it — and all of modern medicine associated with that biotech, all of those advances are linked to geothermal systems and extremophile ecosystems. We got PCR — the polymerase chain reaction, the genetic copy machine that underpins everything in modern biology — because we protected Yellowstone, because we protected the mushroom hot springs, which allowed Thomas Brock to come study them. The Amazon is one of the most biodiverse places on Earth. The western Amazon in Peru is a megabiodiverse region. And within that megabiodiverse region, we have extreme ecosystems. There’s a lot there.”

We protected a hot spring in Wyoming, and it gave us the molecular tool that underpins modern medicine. The Boiling River sits at the intersection of the world’s greatest biodiversity and an extreme geothermal ecosystem we’re just beginning to study, and what it might yield is an exciting mystery.

The City of Gold

Andres: “The big smile just crept across his face and he looks at me and says — you mean you missed it? I was like, what do you mean I missed it? His eyes kind of glanced around, and he said — you missed it. It’s here. It does exist. And it all clicked. When the Inca said, go to the east, to the land of the plant, you’ll find an entire city made entirely of gold — the play on words is life. Gold can be seen as the tears or the sweat of the sun, representing life itself. To the east, in the land of the plant, there is a city of life. You will be walking on interlaced tree roots. You will be walking through great halls of columns of massive trees. There will be a canopy over your head that is the vaulted ceiling of the jungle. Tell me that’s not a city of life. The conquistadors were so focused on the gold, on the short-term monetary asset, that they missed that beautiful jungle that was in front of them.”

Andres: “What’s beautiful about nature — you give nature a chance and it will come back. Life will find a way. It will make it and it will adapt and it will evolve. We just need to keep those cycles in balance. We need to protect that. The jungle can grow back. Without it, there is no future. So what are your options? Charge the windmill.”

Conclusion

When I started working on this series, I viewed the Amazon as mostly a rainforest—a vital and irreplaceable one—but a forest nonetheless. What Carlos, Jimena, and Andres showed me is that I was only seeing one layer of an ancient and interconnected web of life, with systems so deeply interwoven that disrupting any one of them puts the others at risk. And yet at every level, there are people paying close attention and working in their own ways to hold the Amazon together.

In the next episode, we meet the people who have been standing up for the Amazon the longest, and in some cases, have paid the highest price for doing so.

I’m Brooke Mitchell. See you in Episode 6.