Deep in the heart of the Amazon, the world’s largest tropical rainforest, something remarkable is happening. For decades, while the world has worried about its destruction, the trees themselves have been quietly responding to a changing atmosphere. A new study published in Nature Plants reveals that the average size of Amazonian trees has been increasing by about 3.2% every decade. This growth is consistent with the rising levels of carbon dioxide in the atmosphere—a greenhouse gas that is both fueling climate change and, paradoxically, nourishing the forest giants.
The finding is more than just a scientific curiosity. It speaks to the resilience of one of Earth’s most vital ecosystems, while also raising urgent questions about the fragile balance between human activity, climate change, and the natural world.
The Science Behind the Growth
The research was a colossal effort, involving nearly one hundred scientists working across 188 permanent plots scattered throughout the Amazon basin. Over three decades, they carefully monitored tree growth, measuring trunks, tracking canopies, and recording changes in the forest structure. Their conclusion was clear: Amazon trees, large and small alike, are growing bigger.
This widespread increase in size is thought to be linked to the fertilizing effect of carbon dioxide. Plants use CO₂ during photosynthesis, converting it into sugars that fuel growth. With higher concentrations of CO₂ in the atmosphere, trees have more of the raw material they need to grow, and the Amazon is responding in kind.
Professor Beatriz Marimon, who coordinated much of the Brazilian data collection, describes it as a “good news story.” Even amid relentless concerns about deforestation, droughts, and fires, the intact forests of the Amazon are showing an extraordinary ability to thrive.
The Role of the Giants
Not all trees are equal when it comes to storing carbon. The towering giants of the Amazon—some hundreds of years old—hold immense amounts of carbon within their trunks, branches, and roots. When these trees grow larger, they expand the forest’s ability to absorb CO₂ from the atmosphere, helping to offset some of the emissions caused by human activity.
Dr. Adriane Esquivel-Muelbert, joint lead author of the study, emphasizes this point: “Large trees are hugely beneficial for absorbing CO₂ from the atmosphere. This study confirms that, despite climate threats, the effect of CO₂ in stimulating growth is still there. It shows the remarkable resilience of these forests, at least for now.”
But the emphasis on for now is crucial. The growth trend may not last forever. As climate pressures intensify, the resilience of these massive trees could be tested in ways never seen before.
Why Deforestation Threatens the Balance
The research also highlights an uncomfortable truth: not all parts of the Amazon are benefiting equally. While intact forests are growing stronger, vast areas of the Amazon are being cut down, fragmented, or burned. Deforestation not only reduces the number of trees but also destroys the interconnected ecosystems that sustain the giants.
Dr. Rebecca Banbury Morgan warns that we cannot replace what is lost simply by planting new trees: “Large tropical trees are hundreds of years old. We can’t simply plant new trees and expect them to confer anything like the kinds of carbon or biodiversity benefits that the old, natural forest is providing.”
This point is critical. A plantation of young trees cannot replicate the ecological complexity of an ancient rainforest. The Amazon’s resilience depends on its continuity—millennia of growth, decay, and regeneration woven into a living network. Break that network, and even the strongest trees cannot survive.
A Story With Global Implications
The Amazon is often called the “lungs of the planet” because of its role in absorbing carbon and producing oxygen. This study reinforces its central role in mitigating climate change. But it also underlines a paradox: while CO₂ may be fueling growth in the short term, unchecked climate change threatens to destabilize the very systems that allow the forest to thrive.
Professor Tim Baker of the University of Leeds explains it simply: “We knew that the total amount of carbon stored in the trees of intact Amazonian forests has increased. What this new study shows is that all sizes of tree have grown larger over the same period—the whole forest has changed.”
This change is not just a local curiosity—it’s a shift in one of the Earth’s most critical climate regulators. The resilience of Amazon trees has direct consequences for the global fight against climate change.
The Uncertain Future of the Forest Giants
While the study offers hope, it also delivers a warning. As Professor Oliver Phillips points out, “What happens to big trees—including how they deal with increasing climate threats and manage to disperse their seeds—is now mission-critical. The only way the giants will stay healthy is if the Amazon ecosystem stays connected. Deforestation is a huge threat-multiplier and will kill them if we let it.”
The giants of the Amazon are not invincible. Prolonged droughts, increasing fires, and human-driven deforestation could undo the gains revealed in this study. If the forest becomes too fragmented, the cycle of growth and regeneration that sustains these trees may collapse, transforming the Amazon from a powerful carbon sink into a dangerous carbon source.
A Call to Action
As world leaders prepare for COP30 in Brazil, this research serves as both encouragement and warning. The Amazon is showing resilience, adapting to higher CO₂ by growing larger and stronger. Yet that resilience depends on our choices. Protecting intact forests, halting deforestation, and ensuring that the Amazon remains whole is not just a regional issue—it is a global necessity.
The giants of the Amazon have stood for centuries, weathering storms, droughts, and the slow passage of time. They are now growing taller in response to the atmosphere we have altered. Their strength is a gift, buying humanity precious time in the battle against climate change. But like all gifts, it is fragile.
If we wish to keep the Amazon thriving, we must act now to protect it. For the sake of the climate, for biodiversity, and for the generations yet to come, we cannot afford to let the forest giants fall.
More information: Increasing tree size across Amazonia, Nature Plants (2025). DOI: 10.1038/s41477-025-02097-4.
