Africa’s Forests Are Flipping From Carbon Shield To Carbon Source

For years, Africa quietly helped save the planet. Now, the continent’s forests are starting to push the climate problem in the wrong direction.

In a new study in Scientific Reports, an international team led by researchers at the University of Leicester used high resolution satellite data, machine learning and thousands of forest plots to track how much carbon is stored in trees and woody vegetation across Africa. Their conclusion is stark: between 2010 and 2017, Africa’s forests and woody savannas moved from absorbing carbon to emitting it, with a net loss of around 106 billion kilograms of forest biomass per year.

From Continental Sink To Source

Historically, Africa’s forests and woody savannas have played a pivotal role in the global carbon cycle, contributing a substantial share of the world’s carbon removals through photosynthesis. Earlier estimates suggested that sub Saharan Africa acted as a net carbon sink, although the exact size of that sink was hotly debated and sometimes wildly inconsistent across models.

The new analysis cuts through that debate by following the biomass directly. Using satellite derived maps of aboveground woody biomass at 100 meter resolution, the team reconstructed how much living carbon was stored across all major forest and savanna biomes between 2007 and 2017. They validated those maps against an extensive network of field plots and airborne LiDAR surveys, achieving strong agreement even in dense tropical forests where remote sensing has traditionally struggled.

From 2007 to 2010, the picture looked hopeful. Africa gained 439 ± 66 teragrams of aboveground woody biomass per year, roughly a 0.37 percent annual increase. After 2010, however, the sign flipped. Between 2010 and 2015, biomass declined by 132 ± 20 teragrams per year, followed by an additional loss of 41 ± 6 teragrams per year from 2015 to 2017. On average, the weighted mean loss over 2011 to 2017 was 106 ± 16 teragrams of biomass per year, equivalent to about 106 billion kilograms annually.

That is the moment when a continental carbon sink became a carbon source.

The Cost Of Losing Tropical Moist Forests

The study traces that reversal primarily to one biome: tropical moist broadleaf forest. These rainforests hold far more carbon per hectare than savannas or shrublands, with average aboveground biomass densities that can exceed 400 megagrams per hectare in parts of the Congo Basin. When those forests are cut, the climate impact is disproportionately large.

Between 2007 and 2010, tropical moist broadleaf forests in Africa were still gaining carbon, adding about 192 teragrams of aboveground biomass per year. In the following years, that gain collapsed into loss. From 2010 to 2015, the biome lost roughly 70 teragrams per year, and from 2015 to 2017 the loss more than doubled to 154 teragrams per year.

“This study provides critical risk data for Sylvera and the wider voluntary carbon market (VCM), and shows that deforestation isn’t just a local or regional issue, it’s changing the global carbon balance. If Africa’s forests turn into a lasting carbon source, global climate goals will become much harder to achieve. Governments, the private sector, and NGOs must collaborate to fund and support initiatives that protect and enhance our forests.”

These losses are concentrated in the Democratic Republic of Congo, Madagascar and several West African countries, where forest cover loss and forest degradation have accelerated. Satellite maps show biomass falling around settlements, roads and river corridors, as forests are cleared for agriculture, timber and fuelwood or degraded by partial removal of trees.

Savannas tell a more complicated story. Across much of the Tropical Grasslands, Savannas and Shrublands biome, aboveground biomass has increased over the study period, likely due to shrub encroachment and the carbon fertilisation effect of rising atmospheric carbon dioxide that shifts competition toward woody plants. Those gains help, but they do not compensate for the intense losses in dense tropical forests.

How Certain Is The Switch?

The team is cautious about the limitations of satellite based biomass maps, particularly in very dense forests where algorithms tend to underestimate biomass beyond about 350 megagrams per hectare. Even so, their uncertainty analysis points in one direction.

The confidence intervals on net biomass change for Africa do not overlap between the sink period and the source period, which means the shift from sink to source is statistically robust. Comparisons with United Nations Food and Agriculture Organisation country level biomass statistics also show that the new estimates are broadly consistent for nations that hold most of the continent’s forest carbon, such as the Democratic Republic of Congo.

In fact, because the remote sensing products likely underestimate biomass in the densest forests, the authors suggest that their results may be conservative. If more of the “missing” biomass is actually being lost in deforestation hotspots, then the true reversal from sink to source could be even more pronounced than their maps reveal.

“This is a critical wake up call for global climate policy. If Africa’s forests are no longer absorbing carbon, it means other regions and the world as a whole will need to cut greenhouse gas emissions even more deeply to stay within the 2°C goal of the Paris Agreement and avoid catastrophic climate change. Climate finance for the Tropical Forests Forever Facility must be scaled up quickly to put an end to global deforestation for good.”

Closing The Emissions Gap

Overall, the authors estimate that Africa’s forests and woodlands hold about 118 petagrams of aboveground biomass, corresponding to roughly 59 petagrams of carbon. Losing even a small fraction of that stock has consequences that ripple far beyond the continent, especially at a time when global climate agreements are counting on intact forests to help close the emissions gap.

The results dovetail with broader assessments that show a weakening of the global tropical forest carbon sink and a shift toward net emissions in many regions. For Africa, the study concludes, rising biomass losses from 2011 onward are now large enough to tip the continent’s net terrestrial carbon balance toward a source when all pools and fluxes are considered together.

That trajectory is not inevitable. The authors point to forest governance, enforcement against illegal logging, financial incentives such as REDD+, and large scale restoration initiatives like AFR100 and Restor as levers that can slow or reverse biomass loss. High resolution biomass maps, updated regularly, can help target those efforts to the places where they matter most.

The warning is clear, and it is written in the changing weight of trees. Africa’s forests once bought the world time. Without rapid action to protect and restore them, that time runs out faster, and the rest of the planet has to work even harder to keep the climate goals of the Paris Agreement within reach.

Journal: Scientific Reports
Article: “Loss of tropical moist broadleaf forest has turned Africa’s forests from a carbon sink into a source”
DOI: 10.1038/s41598-025-27462-3