Table of Contents
Summary:
Researchers analyzing global carbon fluxes from 1992 to 2019 found that only about 6% of the terrestrial carbon sequestered in this period is stored in living vegetation. Instead, the majority is retained in nonliving reservoirs such as soils, wetlands, and sediments at the bottom of lakes and rivers. This shift is likely due to forest degradation from wildfires, droughts, and deforestation, which have reduced forests’ ability to store carbon.
The study, published in Science, highlights the need to better understand these nonliving carbon pools, many of which are not currently accounted for in global climate models. Researchers also found that a significant share of terrestrial carbon accumulation is linked to human activities, such as dam construction and timber use, which contribute to long-term carbon storage. These findings could improve future climate predictions by refining models of carbon sequestration on land.
Most of the carbon sequestered on land is stored in soil and water
An international study, with the participation of INRAE and the CEA, has discovered that the majority of terrestrial carbon sequestered over the last 30 years is stored in nonliving forms such as the bottom of lakes and rivers, wetlands and soils. Until now, forests were considered to be the main carbon sinks on terrestrial surfaces. However, an analysis of carbon fluxes over the last few decades reveals that, if we take into account gains and losses on a global scale, only around 6% of the total sequestered carbon is stored in live biomass.
This loss could be the result of forest degradation in many parts of the world — caused by fires, droughts and deforestation. Very little is known about the key sequestration processes in these nonliving pools, and currently, many are not included in global models of changes in carbon stocks. These results could help to better predict the future trajectory of these reservoirs and how they are affected by human activities and climate change.
Recent studies have shown that carbon stocks in terrestrial ecosystems are increasing, mitigating around 30% of the CO2 emissions linked to human activities. The overall value of carbon sinks on the earth’s surface is fairly well known — as it can be deduced from the planet’s total carbon balance anthropogenic emissions, the accumulation of carbon in the atmosphere and the ocean sinks — yet, researchers know very little about carbon distribution between the various terrestrial pools: living vegetation — mainly forests — and nonliving carbon pools — soil organic matter, sediments at the bottom of lakes and rivers, wetlands, etc.
This nonliving carbon is derived in particular from the excrement and decomposition of dead plants and animals, and eventually becomes food for soil organisms. While the mechanisms by which carbon accumulates in living biomass are well known — photosynthesis in particular — variations in the nonliving carbon pools are largely unknown and very difficult to measure.
Researchers measured fluctuations in total terrestrial carbon stocks by harmonising a set of global estimates based on different remote sensing technologies and field data between 1992 and 2019. They combined their global estimate with the recent compilation of carbon exchanges between land, atmosphere and oceans to distribute terrestrial carbon accumulation between living and nonliving carbon pools.
A 30% increase in terrestrial carbon sinks over the last decade
The research team, coordinated by Yinon Bar-On (California Institute of Technology), found that around 35 gigatonnes of carbon were sequestered on the Earth’s surface between 1992 and 2019. This accumulation of terrestrial carbon has increased by 30% over the last decade, from 0.5 gigatonnes per year to 1.7 gigatonnes per year. Yet, vegetation, mainly forests, accounts for only 6% of these carbon gains.
Until now, forests were considered to be the main carbon sinks, however, disturbances linked to climate change or human activities — fires, deforestation, etc. — have made them increasingly more vulnerable and now, in certain situations, they could emit almost as much carbon as they accumulate. Nevertheless, they remain important carbon stocks that need to be protected.
The main terrestrial carbon sinks are more enduring
The results show that a substantial fraction of terrestrial carbon accumulation mechanisms is linked to the burial of organic carbon in anaerobic environments, such as the bottoms of natural and artificial bodies of water. More surprisingly, the results indicate that a significant proportion of terrestrial carbon sinks could be linked to human activities such as the construction of dams or artificial ponds, or even the use of timber.
A positive outcome of this study is the discovery that the majority of terrestrial carbon gains are sequestered in a more enduring manner, compared to in living vegetation.
The lack of data on carbon accumulation in soils, bodies of water and wetlands has led current dynamic global vegetation models to greatly overestimate the role of forests in terrestrial carbon sinks. This study identifies key processes in terrestrial carbon accumulation that are not included in current models. As a result, this data could serve as a valuable resource for validating future dynamic global vegetation models in living plant biomass.
Journal Reference:
Yinon M. Bar-On et al., ‘Recent gains in global terrestrial carbon stocks are mostly stored in nonliving pools’, Science 387, 6740, 1291-1295 (2025). DOI: 10.1126/science.adk1637
Article Source:
Press Release/Material by National Research Institute for Agriculture, Food and Environment (INRAE)
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