For years, models warned the Amazon could thin toward savannah under climate stress. New long-term field data suggest a different, more nuanced story: across intact forest plots, trees have been getting larger—turning the basin into a stronger, though not invulnerable, carbon store.
A Twist No One Saw Coming
For decades, scientists have warned that the Amazon rainforest was teetering on the brink—its lush canopy destined to thin into dry savannah under the weight of climate change. But nature, it turns out, had other ideas. Instead of withering away, the trees of the Amazon are bulking up. Not just a few species, not just in select regions—all of them, across the board.¹
It’s an unexpected revelation from one of the most ambitious ecological studies ever carried out in the region. While the world braced for the collapse of Earth’s largest rainforest, something remarkable was unfolding in silence beneath its green roof: the forest was growing stronger.
A Study That Spans Decades And Continents
Picture this: nearly 100 researchers, over 40 years, monitoring 188 separate plots across the South American continent. The project began in 1971 and continued through 2015, with meticulous measurements of tree basal area—the space trunks occupy at ground level—to track how forest biomass changed over time.²
Did you know?
Basal area is a standard way foresters quantify how much of a plot is “wood,” helping compare changes in tree size even across very different sites.
View of the tropical rainforest canopy. Credit: Adriane Esquivel Muelbert
A Forest-Wide Growth Spurt
On average, tree size in the Amazon has grown by about 3.3% per decade since the 1970s.³ That might not sound dramatic, but across a forest the size of a continent, it’s massive. And here’s the kicker: increases show up from the understory to the canopy giants, pointing to a basin-wide structural shift—not a narrow gain among only the tallest trees.
This kind of growth wasn’t supposed to happen. Conventional ecological wisdom suggested only the most established trees would benefit, crowding out the rest. Instead, the study finds a shared advantage across size classes.
When A Pollutant Becomes A Nutrient
So, what’s behind this unexpected transformation? Rising atmospheric CO₂ appears to act like a fertilizer, enhancing photosynthesis and tree growth in intact tropical forests—a mechanism long theorized and increasingly observed in field syntheses.⁴ The Amazon may be making the most of the extra carbon, at least for now.
Everyone’s A Winner In This Forest
Researchers outlined possible responses to more CO₂: big trees only, small trees only, or broad gains. The data align with the “benefits shared” outcome, where trees of many sizes gain in parallel—supporting a more efficient carbon sink as additional carbon is locked into living wood.
The Amazon Fights Back—But For How Long?
Caveat time. The same literature underscores growing risks: parts of Amazonia—especially the southeast—have shifted toward a net carbon source in recent years, linked to deforestation, warming, and fire.⁵ In other words, today’s growth signal in intact plots doesn’t guarantee basin-wide resilience under escalating heat, drought, and land-use change.
The Amazon may be buying us time—but only if intact forests remain protected and degradation is curbed. Squandering that buffer risks losing a crucial ally in the climate crisis just when we need it most.
Footnotes
Nature Plants — “Increasing Tree Size Across Amazonia” — URL: https://www.nature.com/articles/s41477-025-02097-4
Nature Plants — “Increasing Tree Size Across Amazonia” — URL: https://www.nature.com/articles/s41477-025-02097-4
Nature Plants — “Increasing Tree Size Across Amazonia” — URL: https://www.nature.com/articles/s41477-025-02097-4
Earth System Dynamics (EGU) — “The Impacts of Elevated CO₂ on Forest Growth, Mortality, and Carbon Dynamics” — URL: https://esd.copernicus.org/articles/15/763/2024/esd-15-763-2024.pdf
Nature — “Amazonia as a Carbon Source Linked to Deforestation and Climate Change” — URL: https://www.nature.com/articles/s41586-021-03629-6
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Brian is a journalist who focuses on breaking news and major developments, delivering timely and accurate reports with in-depth analysis.
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