Counting 10 billion trees to reveal Africa's hidden carbon secrets
Beyond the continent's famous tropical forests lies a vast, sparse landscape of drylands. By using artificial intelligence to map nearly 10 billion individual trees, scientists have finally achieved the first comprehensive estimate of carbon density across Africa's Saharan, Sahel, and Sudanian zones.
For years, estimating carbon storage in Africa's semi-arid regions was a guessing game. Because tree cover in these landscapes is so dispersed—ranging from dry grasslands to scattered savannahs—previous satellite-based estimates often mistook shrubs and grasses for trees. This error led to significant over-predictions of how much carbon these regions actually hold.
A team of NASA-funded scientists, including lead scientist Dr. Compton Tucker, recently corrected this record. Published in the journal Nature on March 1, 2023, the study utilized sophisticated machine learning to analyze over 326,000 high-resolution commercial satellite images from providers like Maxar Technologies. By processing data from satellites such as QuickBird-2, GeoEye-1, and WorldView-3, the researchers were able to identify trees at an individual level.
The findings revealed a complex reality: while there are far more trees spread across these semi-arid regions than previously believed, they also store less carbon than some models had predicted. The team estimated that roughly 0.84 petagrams—or 840 million metric tons—of carbon are locked within these African drylands. This distinction is vital for climate projections, as the 'carbon residence time' in trees is much longer than the seasonal cycles of grasses and bushes.
This level of precision, which was previously only possible on small, local scales, provides a new foundation for conservation efforts and our global understanding of the carbon cycle.
