The Amazon Rainforest: Earth's Lungs Explained by Science

The Amazon covers about 5.5 million square kilometers and holds an estimated 390 billion trees belonging to roughly 16,000 species. It is the largest remaining tract of tropical rainforest on Earth, and it behaves less like a passive green blanket than like a machine that moves water and carbon around a continent. A 2021 study in Nature found that parts of the southeastern Amazon now emit more carbon than they absorb. The popular nickname, "lungs of the Earth," gets the chemistry wrong but points at something real, and this article explains both halves.

Key takeaways

• The "lungs" label is misleading: the Amazon's net contribution of oxygen to the atmosphere is approximately zero, because the forest consumes nearly as much oxygen as it makes.
• Its real planetary roles are carbon storage, about 10% of the carbon held in ecosystems worldwide by one summary, and rainfall recycling that reaches as far as the La Plata basin.
• Scientists have proposed that clearing 20 to 25% of the forest could push parts of it into a self-reinforcing shift toward savanna-like vegetation, and about 20% has already been cleared across the basin.
• Brazilian deforestation fell by roughly 83% between 2004 and 2012, rose again after 2018, and was lower again in 2024, which shows policy can move the numbers.
• Indigenous territories and protected areas hold 58% of the region's carbon, according to a 2020 analysis.
• Planting trees helps only under the right conditions, and it cannot substitute for stopping the clearing of intact forest.

Why "lungs of the Earth" is the wrong metaphor

Lungs take in oxygen and release carbon dioxide. A forest does the reverse during the day: leaves absorb carbon dioxide (CO₂) and release oxygen through photosynthesis, the process that turns light, water, and CO₂ into sugar. Our explainer on how photosynthesis works covers the chemistry in detail.

The part the slogan ignores is that the forest also breathes in oxygen. Every living tree, fungus, insect, and microbe respires, and when plants die and decay, microbes consume oxygen to break them down. In a mature forest the two flows nearly cancel. According to a reference summary of the Amazon, the claim that the forest produces more than a quarter of Earth's oxygen refers to oxygen turnover, and its net oxygen contribution is approximately zero.

Think of a family that earns a large salary and spends almost all of it. The paycheck is huge, but the savings are tiny. The Amazon's photosynthesis is the paycheck; respiration and decay are the spending. What the forest actually saves is carbon, which sits in wood, roots, and soil for centuries, and that is where its climate importance lies.

What the Amazon actually does for the climate

Two functions matter most: it stores carbon, and it moves water.

The carbon vault

The summary cited above puts the carbon held in the Amazon's evergreen forests at about 10% of the carbon stored in ecosystems worldwide, on the order of 110 billion metric tonnes of carbon. A 2020 analysis in PNAS found that Indigenous territories and protected natural areas held 58% of the Amazon region's carbon (41,991 million tonnes) in 2016.

For decades the forest acted as a net sink, absorbing more carbon than it released. That sink is weakening. In a Nature study from 2015, Brienen and colleagues analyzed three decades of data from 321 plots and found that the net increase in above-ground biomass fell by one-third in the most recent decade compared with the 1990s. Trees were growing faster but dying younger, which shortens how long carbon stays locked up. A later study by Hubau and colleagues, published in Nature in 2020, concluded that carbon uptake by intact tropical forests peaked in the 1990s.

Drought makes the swings dramatic. The reference summary reports that the 2010 drought released about 8 gigatons of CO₂, compared with a typical annual absorption of 1.5 gigatons. That is one dry year erasing several years of uptake, and it is why scientists watch drought frequency closely.

The water pump

Trees pull groundwater through their roots and release it as vapor through pores in their leaves, a process called transpiration. In a rainforest this adds up to an enormous flow of moisture into the air. The vapor drifts downwind, condenses, and falls again as rain, which the next patch of forest recycles once more. Scientists call this moisture recycling, and some popular writers call the airborne streams "flying rivers."

The effect reaches well beyond the forest. Zemp and colleagues, writing in Atmospheric Chemistry and Physics in 2014, found that cascading moisture recycling contributes about 9 to 10% of total precipitation over South America and 17 to 18% over the La Plata basin. The same study estimated that the share of La Plata's wet-season rain that originates in the Amazon rises from 18 to 23% to 24 to 29% when the cascade is counted. The southwestern Amazon appeared to be a particularly important relay station.

In plain terms, farmland far from the forest may depend on rain that the forest made. This is the awkward logic of clearing forest to expand agriculture: the pasture may eventually get less of the rain that makes pasture possible. For the basics of how evaporation and rainfall connect, see how the water cycle works.

Biodiversity in numbers

The Amazon holds about one in ten of the world's known species. The reference summary lists at least 40,000 plant species, 2,200 classified fish species, 1,294 birds, 427 mammals, 428 amphibians, 378 reptiles, and roughly 2.5 million insect species. Many insects remain undescribed.

Tree diversity is better quantified than most. Ter Steege and colleagues combined data from 1,170 plots and estimated in Science (2013) that Amazonia has about 16,000 tree species. Only about 227 of them, or 1.4%, make up half of all trees. Those "hyperdominant" species are mostly habitat specialists, not all-purpose survivors. The remaining thousands are rare, which means each is vulnerable to local clearing.

Group	Documented in the Amazon	Note
Plant species	At least 40,000	Includes about 16,000 tree species (estimate)
Fish	About 2,200 classified	More are undescribed
Birds	1,294	Reference summary
Mammals	427	Reference summary
Amphibians	428	Reference summary
Reptiles	378	Reference summary
Insects	About 2.5 million species (estimate)	Most not formally described

Biodiversity ties directly to place. Many Amazonian species live in narrow ranges and need large intact patches, so habitat loss translates quickly into extinction risk. For a ranking of how the Amazon's host nations compare with others, see our list of countries with the most biodiversity. Another tropical ecosystem with a similar dependency between structure and species is the reef, covered in how coral reefs work.

The people who live in the forest

More than 30 million people live in the Amazon, from about 350 ethnic groups, according to the reference summary. Indigenous peoples make up about 9% of the population, 3,344 formally acknowledged Indigenous territories exist, and about 60 groups remain largely isolated.

These communities matter for conservation, not only for ethics. The PNAS analysis found that Indigenous territories and protected areas together accounted for just 10% of the region's net carbon loss (about 130 million tonnes, out of 1,290 million tonnes lost region-wide), even though they hold 58% of the carbon. In other words, the lands where people hold secure tenure and legal protection lost carbon far more slowly than the rest of the forest.

That finding comes with a caveat. The same paper found that degradation and disturbance, meaning logging, fire, and edge effects that damage forest without clearing it, made up 47% of regional emissions. In seven countries they accounted for more than 75% of carbon losses. Counting only clear-cut deforestation understates the damage.

The tipping point problem

A tipping point is a threshold beyond which a system shifts to a different stable state, often one that is hard to reverse. For the Amazon, the feared shift is from closed-canopy rainforest to open, savanna-like vegetation with far less carbon storage and rainfall generation.

The mechanism is a feedback loop. Forest cover creates its own humid microclimate. When forest is cleared, the land heats up, transpiration falls, local humidity drops, and rainfall decreases. A drier forest burns more easily, and fire kills trees, which cuts transpiration further. Each turn of the loop makes the next one more likely, like a thermostat wired backward.

What the evidence says

Three lines of research frame the debate, and they differ in strength.

Study	Type	Key finding
Lovejoy and Nobre, Science Advances, 2018	Editorial and synthesis	Tipping point at 20 to 25% deforestation in eastern, southern, and central Amazonia; suggested keeping clearing below 20%
Boulton, Lenton, and Boers (preprint 2021, later published 2022)	Analysis of satellite vegetation data, 1991-2016	Resilience has declined since about 2003, most steeply in drier regions and near human activity
Flores and colleagues, Nature, 2024	Review and spatial analysis	By 2050, 10 to 47% of Amazonian forests could be exposed to compounding disturbances

The Lovejoy and Nobre piece is an editorial in Science Advances, not a single experiment, and it argues that deforestation, climate change, and fire together set the threshold. It also noted that many studies indicate 4 degrees Celsius of global warming would be a tipping point for degraded savanna in most of the central, southern, and eastern Amazon, and that the droughts of 2005, 2010, and 2015 to 2016 "could well represent the first flickers" of the tipping point. The dry season in the southern and eastern Amazon had lengthened over the previous two decades.

The Boulton study used early-warning indicators, statistical signals such as slower recovery after disturbance, which can precede a shift. The authors reported resilience had declined since about 2003. The Flores paper reviewed five main drivers of water stress, including warming, drought, deforestation, and fire, and identified three plausible ecosystem trajectories.

The numbers are estimates with real uncertainty. The 20 to 25% threshold is a model-based range, not a measured cliff, and the forest will not change state everywhere at once. Researchers expect patches in the drier south and east to shift first. The shared message is that the system is under compounding stress, so the safe margin is shrinking.

Where the Amazon is already a carbon source

In 2021, Gatti and colleagues published an unusual dataset in Nature. They used 590 aircraft profiles of CO₂ and carbon monoxide at four sites from 2010 to 2018, measuring the air above the forest instead of relying on tree plots.

They found carbon emissions were higher in eastern Amazonia, mainly because of fire, and that the southeast acted as a net carbon source. Over the previous 40 years, the east had experienced more deforestation, warming, and moisture stress, especially in the dry season. The authors linked the intensifying dry season and rising deforestation to more fire and higher emissions.

A fair reading is that this is a regional signal, not a verdict on the whole Amazon: the southeast was the part identified as a net source. The result does show that a forest can flip from helping the climate to harming it when it is stressed.

Deforestation: causes, trends, and what worked

Satellite monitoring by Brazil's space agency, INPE, tracks forest loss in the Brazilian Amazon each year. The figures below come from the summary table of those data; the page gives 27,423 km² for 2004 in its text and 27,772 km² in its table, so treat the earliest value as approximate.

Year	Forest loss, Brazilian Amazon (km²)	What was happening
2004	About 27,000	Peak year
2012	4,571	After years of enforcement and monitoring
2018	7,536	Rising
2021	10,476	Higher
2022	About 11,600	Highest of the years listed after 2004
2024	6,288	Lower again

The drop from the 2004 peak to 2012 is roughly 83%. That is among the best documented conservation successes, and it is commonly credited to satellite monitoring paired with enforcement. The later rise suggests that gains can reverse.

What drives the clearing

Most Amazon deforestation ends up as pasture. The reference summary attributes about 80% of Brazilian Amazon deforestation to cattle ranching, and reports that about 70% of formerly forested land in the Amazon, and 91% of land deforested since 1970, has been used as livestock pasture. Soy cultivation is the other commodity most often linked to clearing.

Across the whole basin, about 20% of the forest has been deforested and another 6% is highly degraded, according to the same summary. Brazil holds about 60% of the forest, so its policies carry the most weight. Our explainer on deforestation, its causes and solutions covers the global pattern, and the ranking of countries with the most forest cover puts Brazil in context.

Policy tools in play

Tool	What it does	Status
Soy Moratorium	Voluntary agreement aimed at keeping soy from newly cleared Amazon land out of supply chains	Began 2006; described as weakening; a 2015 study found about 1% of new soy expansion after eight years came at the expense of forests
COP26 pledge	More than 100 countries, including Brazil, agreed to end deforestation by 2030	Made in November 2021
EU Deforestation Regulation	Requires proof that cattle, soy, palm oil, wood, cocoa, coffee, and rubber products are not from recently deforested land	Latest amendments (December 2025) set application for large and medium operators at December 30, 2026, and for micro and small operators at June 30, 2027
Tropical Forest Forever Facility	Pays countries $4 per hectare of intact forest, deducting $400 per hectare deforested and $100 per hectare degraded	Proposed for launch at COP30 in Belém in November 2025; planned fund of $125 billion, not a completed raise; 20% of payments to go to Indigenous peoples and local communities

Details on the EU rules come from the European Commission, and the facility's design is summarized on its reference page. Because implementation dates in this area have changed more than once, check the Commission page for the current schedule.

None of these tools is a silver bullet. Consumers in Europe, China, and North America buy the beef and soy, which makes deforestation partly an import problem. At the same time, local politics, land speculation, and illegal grabbing of public land play large roles that trade rules reach only indirectly.

Restoration: planting trees is not enough

Tree-planting pledges are popular, but ecologists warn against treating them as a simple fix. Karen Holl and Pedro Brancalion titled their 2020 commentary in Science "Tree planting is not a simple solution", a title that captures the concern: planting trees is easy to announce and hard to do well, because survival, species choice, and land tenure all matter.

Natural regeneration, in which cleared land is simply left to regrow from seed banks, roots, and animal-dispersed seeds, is often more cost-effective than planting. Cook-Patton and colleagues compiled about 13,000 field measurements of carbon accumulation in regrowing forests for a Nature paper in 2020 and produced a global map at roughly 1-kilometer resolution. They found more than a 100-fold variation in accumulation rates and estimated that the maximum climate mitigation potential of regrowth is about 11% lower than previously reported. Climate explained more of the variation than land-use history.

The practical lesson is that regrowth works best where rainfall is adequate, seed sources are nearby, and there is no new clearing or fire. Those are exactly the conditions under pressure in the Amazon's drier south and east. A regrowing forest also takes decades to approach the carbon and species richness of old forest, which is why protecting intact forest comes first.

Common misunderstandings

"If the Amazon burned, we would run out of oxygen." No. Net oxygen from the forest is approximately zero, and the atmosphere holds an enormous reserve compared with what any forest turns over. The danger of burning is the CO₂ released and the loss of rainfall and species, not suffocation.

"The Amazon is almost gone." It is not. About 20% of the basin has been deforested, and the largest intact blocks remain. The point of the tipping-point research is that the remaining forest is more fragile than its size suggests, not that it has vanished.

"Deforestation only matters in Brazil." Brazil holds about 60% of the forest, but the Amazon also spans parts of Bolivia, Peru, Colombia, and other countries, and global supply chains pull on all of them.

"Planting trees offsets clearing forest." The carbon and biodiversity of intact old forest take decades to centuries to rebuild, so offsetting a hectare of clearing with a hectare of planting is not an even trade.

"Climate change and deforestation are separate problems." They reinforce each other. A hotter, drier climate lengthens the dry season and raises fire risk, while clearing reduces the moisture that buffers drought. For the wider science of warming, see climate change science: how it works.

FAQ

Q: Why is the Amazon called the lungs of the Earth? A: The nickname refers to the forest's huge photosynthesis, but it is misleading because the forest also consumes oxygen through respiration and decay, so its net oxygen contribution is approximately zero. The Amazon's real climate roles are storing carbon and recycling rainfall.

Q: What is the Amazon tipping point? A: It is a proposed threshold beyond which deforestation, warming, and fire could push parts of the forest into a savanna-like state. Lovejoy and Nobre suggested that 20 to 25% deforestation could trigger this in the eastern, southern, and central Amazon, and that clearing should stay below 20%. It is a model-based estimate, not a precise line.

Q: How much of the Amazon has been destroyed? A: Across the whole basin, about 20% has been deforested and another 6% is highly degraded, according to one summary of the literature. Rates differ by country and region, and Brazil holds about 60% of the forest.

Q: Is the Amazon a carbon source or a carbon sink? A: Overall it has been a net sink, but the sink is weakening, and a 2021 Nature study based on aircraft measurements found the southeastern Amazon acting as a net carbon source, driven largely by fire. The balance varies by region and by year, and drought years can reverse it.

Q: Has Brazilian deforestation gone up or down recently? A: Annual loss in the Brazilian Amazon fell from about 27,000 km² in 2004 to 4,571 km² in 2012, rose to about 11,600 km² in 2022, and was 6,288 km² in 2024, according to INPE-based figures. The trend has depended heavily on enforcement and policy.

Q: Do Indigenous lands really help protect the forest? A: A 2020 PNAS analysis found that Indigenous territories and protected areas held 58% of the Amazon region's carbon but accounted for only about 10% of its net carbon loss. Secure land rights are associated with lower loss, though the study also shows that degradation can still occur inside protected lands.

Q: What can individuals do? A: The evidence is strongest for supply-chain and policy changes, but consumer choices matter at the margin, since most clearing becomes pasture and soy. Our guide to reducing your carbon footprint ranks actions by measured impact, and the list of countries with the highest CO₂ emissions shows where the largest flows originate.

The takeaway

The Amazon deserves protection for reasons that are more interesting than the lungs slogan. It stores a large share of the world's ecosystem carbon, it recycles rainfall across a continent, and it holds roughly one in ten known species. Because those functions depend on the forest staying large and wet, the risk is nonlinear: each additional hectare cleared, burned, or dried makes the next loss more likely.

The most encouraging fact in the data is that the trend has bent before. Brazil cut forest loss by about 83% between 2004 and 2012, and the 2024 figure was well below the 2022 level. The most sobering fact is that the forest's resilience has been declining since about 2003 even as that policy worked. Protecting what is left, and keeping it wet, is worth more than any amount of replanting.

Sources

• Gatti et al., "Amazonia as a carbon source linked to deforestation and climate change," Nature 595 (2021), doi:10.1038/s41586-021-03629-6
• Brienen et al., "Long-term decline of the Amazon carbon sink," Nature 519 (2015), doi:10.1038/nature14283
• Walker et al., Amazon Indigenous territories and protected areas carbon dynamics, PNAS 117 (2020), doi:10.1073/pnas.1913321117
• Zemp et al., "On the importance of cascading moisture recycling in South America," Atmospheric Chemistry and Physics 14 (2014), link
• Flores et al., "Critical transitions in the Amazon forest system," Nature 626 (2024), doi:10.1038/s41586-023-06970-0
• European Commission, EU Deforestation Regulation

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• Deforestation Explained — Causes, Effects, and Real Solutions
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• How Coral Reefs Work — and Why They're Dying