A new study based on 30 years of satellite data analysis indicates that small forest clearings, often smaller than 0.1 hectares, account for more than 56% of carbon loss, even though they make up only 5% of the total cleared area.
The researchers used data obtained from the European Space Agency's Biomass satellite. It is the first satellite equipped with a space radar. It is able to "see" through dense forest canopy and measure the amount of carbon stored in trunks, branches and biomass. The satellite system captures detailed structural information, offering a view of how the world's forests lose and regain carbon. According to a new study that challenges long-standing assumptions about the causes of emissions in the world's most important forests, it has been established that small forest clearings, often no larger than a football pitch, cause more than half of all carbon loss in the tropical region.
Published in nature.com, the study provides the most detailed reconstruction to date, showing how the amount of carbon in tropical forests in the Northern and Southern Hemispheres has changed over the past 30 years. Scientists from France's Laboratory of Climate and Environmental Sciences (LSCE), working together with specialists from the European Space Agency's Climate Change Initiative, found that clearings smaller than two hectares account for 56% of total carbon loss. The area of these small clearings makes up only 5% of the total affected area.
The research team used a high-resolution recording method that combines satellite observations of areas of less than a hectare with new biomass recovery curves, making it possible to map carbon losses and gains at a 30-metre scale. Analysis of the data indicates that the reduction in tropical rainforest area between 1990 and 2020 caused a carbon loss of almost 16 billion tonnes, while in tropical dry forests there was an approximate balance between losses caused by deforestation and natural regeneration. In recent years, several studies have pointed to agricultural expansion as the main cause of deforestation.
The study's lead scientists, Yidi Xu (Yidi Xu) and Philippe Ciais (Philippe Ciais), note that the ESA biomass maps delivered the breakthrough by providing unprecedented detail. "Unlike previous global models, which relied on simplified assumptions or continental averages, our approach allowed us to record how the type and scale of disturbance and local climatic conditions affect forest regeneration," the scientists emphasised. "This allowed us to discover that most tropical carbon loss is driven 'quietly' not by large-scale logging or forest fires, but by small-scale human impact."
Most of these sites are not linked to logging or catastrophic fires; rather, they reflect the cumulative impact of everyday human activity — expanding agricultural land, creating pasture, building roads and establishing settlements. In humid rainforests, these disturbances often do not encourage regeneration, locking in long-term emissions and amplifying the climate impact of every hectare lost.
The study also shows that disturbances are increasingly affecting denser, more carbon-rich humid forests. Although undisturbed tropical forests still act as carbon stores, their capacity to offset losses elsewhere is now only just sufficient to keep the overall tropical carbon balance close to neutral. The study's findings have significant implications for climate policy, for example in Africa, where relatively small-scale disturbances predominate. The scientists argue that curbing agricultural expansion could deliver far greater climate benefits than previously recognised. Regenerating forests must be protected from repeated disturbance in order to preserve their carbon storage potential.
Clement Albergel (Clement Albergel), head of the ESA's Actionable Climate Information section, emphasised that the study reinforces the importance of long-term satellite monitoring. "As tropical forests face ever more frequent threats, both from climate change and from fires and human impact, this study highlights an essential fact: even the smallest clearings matter. Using the ESA biomass maps, we are gaining unprecedented insight into how ecosystems lose and regain carbon. This knowledge is vital if we are to protect ecosystems while there is still time."