Unveiling the Dominance of Nonliving Carbon Pools in Terrestrial Sinks

Recent research led by Yinon Bar-On from the California Institute of Technology found that terrestrial carbon sequestration increased by 30 % over the past decade, reaching 1.7 gigatons per year. However, forests accounted for only 6 % of these gains. The study, published in Science, reveals that much of the carbon is stored in anaerobic environments, such as water bodies.

Recent studies indicate that carbon stocks in terrestrial ecosystems are increasing, offsetting approximately 30 % of CO₂ emissions from human activities. While the total value of carbon sinks on Earth's surface is relatively well understood—based on the planet's carbon balance, anthropogenic emissions, atmospheric accumulation, and ocean sinks—researchers have limited knowledge of the carbon distribution among terrestrial pools. These pools include living vegetation, primarily forests, and nonliving carbon pools, such as soil organic matter, sediments in lakes and rivers, and wetlands.

Nonliving carbon primarily originates from the excrement and decomposition of dead plants and animals, which eventually serves as food for soil organisms. While the mechanisms of carbon accumulation in living biomass, particularly through photosynthesis, are well understood, variations in nonliving carbon pools remain largely unknown and difficult to measure.

To address this, researchers analyzed fluctuations in total terrestrial carbon stocks by harmonizing global estimates derived from various remote sensing technologies and field data collected between 1992 and 2019. They combined their global estimates with a recent compilation of carbon exchanges among land, atmosphere, and oceans to allocate terrestrial carbon accumulation between living and nonliving carbon pools.

A 30 % Increase in Terrestrial Carbon Sinks Over the Last Decade

Forests have long been considered the primary carbon sink. However, disturbances from climate change and human activities, such as fires and deforestation, have made them more vulnerable. In some cases, forests may release nearly as much carbon as they absorb. Despite these challenges, forests remain crucial carbon stocks that must be preserved.

The Main Terrestrial Carbon Sinks Are More Enduring

The findings suggest that human activities, such as dam construction, artificial pond creation, and timber use, may influence a significant portion of terrestrial carbon sinks. A key positive outcome of the study is the discovery that most terrestrial carbon gains are sequestered more permanently than in living vegetation.

The lack of data on carbon accumulation in soils, bodies of water, and wetlands has caused current dynamic global vegetation models to significantly overestimate the role of forests in terrestrial carbon sinks. This study highlights critical processes in terrestrial carbon accumulation that are missing from existing models. As a result, this data could serve as a valuable resource for improving and validating future dynamic global vegetation models related to living plant biomass.

Journal Reference:

Bar-On, Y. M., et al. (2025). Recent gains in global terrestrial carbon stocks are mostly stored in nonliving pools. Science. doi.org/10.1126/science.adk1637.