Quantifying the Global and Regional Contribution of Terrestrial Carbon Pools to the Land Sink

Over the past several decades, terrestrial ecosystems have offset a ≈30% of anthropogenic CO2 emissions through increased CO₂ uptake. While this carbon enters the biosphere through photosynthesis into biomass, its current distribution across different pools—such as live biomass, dead biomass, and soil and sedimentary organic carbon—remains uncertain. The partitioning of carbon into these pools impacts future terrestrial carbon storage because they have different turnover times and sensitivities to environmental change. By harmonizing a set of global estimates for changes in live woody biomass, we found that while ≈35±14 gigatons of carbon (GtC) have been sequestered on land between 1992-2019, live woody biomass changed by only ≈2±7 GtC. These findings contrasted with results from global vegetation models, which show sustained increases in live biomass. We highlight key processes that are not currently included in models and can account for a large fraction of this discrepancy such as forest degradation or fluxes related to inland waters. We infer that recent gains in terrestrial carbon stocks are sequestered as non-living organic matter in a combination of dead biomass, soils, and other sedimentary deposits. These results suggest that terrestrial carbon accumulated in recent decades might be more persistent than previously appreciated, and that a substantial fraction of it is intimately linked to human activities such as river damming, wood harvest, and waste treatment.