Recent studies have shown that carbon sequestration in terrestrial ecosystems is increasing, mitigating around 30% of the CO2 emissions linked to human activities.
The overall value of carbon sequestration on the Earth’s surface is fairly well known, as it can be deduced from the planet’s total carbon balance anthropogenic emissions.
However, researchers know very little about carbon distribution between the various terrestrial pools: living vegetation, such as forests, and non-living carbon pools, which include soil organic matter, sediments at the bottom of lakes and rivers, and wetlands.
This non-living 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 non-living carbon pools are largely unknown and very difficult to measure.
A 30% increase in terrestrial carbon sinks over the last decade
Researchers measured fluctuations in total terrestrial carbon sinks 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 non-living carbon pools.
They 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.
However, vegetation, mainly forests, accounts for only 6% of these carbon gains. Until now, forests were considered to be the main forms of carbon sequestration.
However, disturbances linked to climate change or human activities have made them increasingly more vulnerable, and now, they could emit almost as much carbon as they accumulate.
Nevertheless, they remain important carbon stocks that need to be protected.
Accumulation from human activities
The results show that a substantial fraction of terrestrial carbon accumulation mechanisms are 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 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.
Future research: Expanding our knowledge of living and non-living carbon sinks
The recent increase in carbon sequestration provides a promising, though complex, outlook for mitigating climate change.
While forests remain vital carbon stocks, the study reveals that non-living carbon pools, such as soils, wetlands, and bodies of water, are playing a much larger role than previously understood.
The increase in terrestrial carbon sinks over the past decade, much of which is linked to human activities like dam construction, suggests that there are additional, overlooked opportunities for enhancing carbon storage. However, the vulnerability of ecosystems like forests to climate change and human activities highlights the need for comprehensive protection and more accurate carbon models.
By expanding our understanding of how carbon accumulates in both living and non-living ecosystems, we can better design strategies to preserve and enhance these critical carbon sinks for the long-term benefit of the planet.
