The trees of the Amazon rainforest are getting larger, and scientists believe rising carbon dioxide levels in the atmosphere are the reason why.
A new international study published in Nature Plants found that the average size of Amazonian trees has increased by about 3.2% every decade for at least the past 30 years.
The study involved nearly one hundred scientists from more than 60 universities worldwide, who monitored trees across 188 long-term plots in the Amazon.
The results suggest that higher levels of carbon dioxide, a key driver of climate change, may also be fertilizing the trees and stimulating their growth.
Professor Beatriz Marimon from Universidade do Mato Grosso in Brazil, who helped oversee data collection, called the finding “a good news story.”
She noted that while deforestation and climate change continue to pose serious threats, intact forests still show resilience, with even the largest and oldest trees continuing to grow.
The research shows that both small and large trees are benefiting from the extra carbon dioxide. This growth has big implications for the climate, since larger trees are more effective at absorbing carbon from the atmosphere.
Dr. Adriane Esquivel-Muelbert of the University of Cambridge, one of the study’s lead authors, explained that this underscores the critical role of tropical forests in slowing global warming.
“Large trees are hugely beneficial for absorbing CO₂,” Esquivel-Muelbert said. “Despite fears that climate change might weaken the Amazon’s ability to act as a carbon sink, the effect of CO₂ in boosting growth is still happening. These forests are remarkably resilient—at least for now.”
However, the researchers also caution that deforestation and fragmentation of the Amazon threaten this resilience. Dr. Rebecca Banbury Morgan of the University of Bristol stressed that the destruction of ancient forests cannot be undone simply by planting new trees. Many of the Amazon’s giants are hundreds of years old, and their size and biodiversity value cannot be quickly replaced.
Professor Tim Baker of the University of Leeds, another senior author, added that this is the first study to show how CO₂ has systematically altered the tree-size structure of Amazon forests. The increase is not limited to a few species; rather, trees of all sizes have grown larger, reshaping the entire forest.
But the future of these giants is uncertain. Professor Oliver Phillips, also of the University of Leeds, warned that deforestation multiplies risks for big trees, from climate stress to seed dispersal challenges.
“What happens to big trees is mission-critical,” he said. “They will only stay healthy if the Amazon remains intact. If deforestation continues, we risk losing them.”
The study offers a rare piece of optimism in the fight against climate change—evidence that nature is still responding to rising CO₂ by growing stronger. Yet it also highlights the urgent need to protect the Amazon, one of the planet’s most important defenses against global warming.
