By Dan Drollette Jr March 12, 2025. Carlos Afonso Nobre is a Brazilian scientist and meteorologist who is mainly highlighted in global warming-related studies.
For roughly 65 million years, the forests of the Amazon were resilient to changes in the climate. But that is changing rapidly, as the region is exposed to unprecedented stress from global warming, extreme droughts, and fires, leading to massive deforestation—even changing the biome itself, from that of a rainy forest rich in biodiversity to a much drier and less-diverse savannah.
Dan Drollette Jr: In 2019, you co-wrote an open letter in Science Advances called “Amazon tipping point: Last chance for action.” How have things changed since then? Is it better, worse, the same?
Carlos Nobre: I think things are becoming much worse, particularly from the second half of 2023 onwards. We had record-breaking drought in the Amazon, as well as record-breaking forest fires. In 2024 we had more than 180,000 forest fires all over the Amazon, with close to 148,000 of them in the Brazilian Amazon alone. 98% were of man-made origin. We suspect that the man-made wildfires were mostly criminal in origin.
The point is that the Amazon had record-breaking drought, and record-breaking fires—which also put the Amazon at its lowest river level in history. All these issues came together, to make 2023 and 2024 closest to the tipping point ever.
When people are talking about tipping points in the Amazon, what do they mean, exactly?
There are really two ways of looking at how close the Amazon is to a tipping point.
The first one is that over a huge area of the southern Amazon—from the Atlantic all the way to the lowlands of Bolivia, Peru, and Colombia, along with all the southern Brazilian Amazon— the dry season is becoming lengthier and lengthier, decade after decade.
This is an area close to 2.5 million square kilometers, that over the last 45 years, has been seeing the dry season get 5 weeks lengthier.
The dry season over this southern portion used to be 3 to 4 months—and even during the driest part of the dry
season, there was a little bit of rain, maybe 40 or 50 millimeters.
But what we are seeing now is that the dry season is not only 5 weeks lengthier, but the rainfall during this season is about 20 or 30% less—and the temperature is 2, or 3˚C warmer.
So, as I said, where historically the dry season lasted 3 to 4 months, now it’s already 4 to 5 months, which is dangerously close. As soon as it reaches 6 months, that’s the point at which you hit the climate envelope. What was jungle becomes savannah, the kind of biome found south of the Amazon and north of the Amazon. So that’s one reason why we say we are very close to the tipping point.
Number two is that studies have shown that in the south-eastern Amazon over the last 15 years, some forestland has stopped being a carbon sink and has started to become a carbon source. And that’s significant: Historically, forests remove more than 30% of all the carbon dioxide that we release into the atmosphere; as late as the 1990s, the Amazon rainforest was still removing close to 1 billion tons—and in some years, closer to 1.5 billion tons—of carbon dioxide. So it’s very concerning that in this area of the Amazon, the forest itself has become a carbon source. And it’s become a carbon source because the dry season is longer, the temperature is much hotter, and tree mortality is increasing tremendously.
So I’m saying that these two factors are going on at the same time —the dry season in the southern Amazon is 5 weeks lengthier, and in the southeastern Amazon, the forest has become a carbon source. Consequently, it’s obvious that the Amazon is at the edge of a tipping point.
Why is the dry season becoming 5 weeks longer?
This is a synergistic combination of droughts induced by global warming, combined with deforestation in the Southern Amazon mostly for pastures for cattle ranches. And when those forests go, that has a huge effect.
Over tens of millions of years of ecological evolution, many trees in the Amazon have developed a very deep rooting system, that gets down to 7, 10, or even 12 meters below the surface, where they can access water deep underground. It’s unique—no other forest in the world, has this. And what it means is that even when there is more solar radiation, there is plenty of water deep in the soil that the trees can pump up.
But when you replace the trees of that forest with pasture, what happens is that the kinds of plants that live in pasture have very, very shallow rooting systems, going only about 1.5 meters down. So, during a severe dry season, the pasture-associated tree is unable to capture moisture. The amount of what we call “evapotranspiration” is about one-third to one-fourth that of trees in the Amazon rainforest.
This is happening across the large areas in the Amazon: something like 1 million square kilometers that’s turned to pastures
Once an area of rainforest has turned into savannah, is there much chance of it turning back on its own to the kind of jungle that was there before?
No, not really, because it’s a self-degradation system, where it builds on itself. And once it reaches that point—most likely around 2050—then about half to 70% of the rainforest will become this degraded, savannah-like biome.
What many studies show is that if we exceeded two to 2.5˚C, and have only 20 to 25% of the Amazon forest left, then we are going to reach the tipping point where it will self-degrade. And if that happens, then we release more than 200 billion tons of carbon dioxide into the atmosphere, making it almost impossible to keep global warming down.
How would you reply to someone—say, someone here in North America —who says “Okay, so the Amazon dries up in the Southern Hemisphere. It doesn’t affect us up here.”
I would say that there have been numerous science papers published, which show that this drying-up process means that there would be at least a 30% reduction in rainfall. And studies have shown as soon as you do something on that scale in the Amazon, then you start generating atmospheric wave effects that propagate to the north, through Central America, Mexico, and all the way to California. And these waves would induce even more droughts in California, similar to what an El Nino does.
And a second impact is what I already mentioned—that within 30 to 50 years, we are going to lose at least 202 billion tons of carbon, making it impossible to keep the temperature rise below 1.5˚C.
And a third impact I’d tell them is that the degradation of the Amazon rainforest raises tremendously the risk of epidemics and pandemics. For the first time in 500 years, we are having epidemics that can be traced to the Amazon. Two of them are especially concerning: One is a virus called mayaro fever, and the other is oropouche fever. Both are likely native to the Amazon, and have now spread all over Brazil. They are transmitted by infected mosquitoes; there are no vaccines to prevent them or medicines to treat them. There are least 48 such zoonoses that we know of from this region—that is, diseases that can be passed from animals to humans. So there will be pandemics, yes, and that will affect the whole planet, including North America.
And a fourth impact is that if the Amazon goes, then we are going to lose the largest level of biodiversity on the planet.
What is the biggest challenge?
The big challenge is how to combat organized crime. As I said, most of the fires in the Amazon were man-made. And a lot of those fires were caused by organized crime, which historically has been responsible for about 80% of deforestation in the history of the Amazon. It’s all associated with drug trafficking, illegal gold mining, illegal selective logging, and illegal wildlife trafficking.
Studies show that, in some years, the economy of this organized crime in the Amazon is about $280 billion a year. Organized crime is involved in the illegal land market. They go to public lands, or areas that fall into gray areas—lands that were not clearly designated as public, or as conservation units, or as indigenous territories. So they go set fire to the forest, bring in cattle, start a ranch, and sell it. And it seems that a lot of what happened last year was related to organized crime.