Carbon stocks tougher than we thought

Where does carbon go when carbon goes out? More than we thought ends up in non-living material ... a persistent form of storage.

SL Staff B

05 Apr 2025 • 2 min read

You'd think not much was left to learn about carbon dioxide, right? People, factories, monkeys, Hummers ... lots goes on to emit CO₂. You know the list. And a few things absorb carbon: oceans, geological processes, grasslands ... and, to quote Michael Pollan: "mostly plants".²

Carbon mysteries are still left for us to solve. Notably, we can measure how much carbon dioxide enters and exits the atmosphere ... and the totals haven't added up the way we thought.

Specifically, we can estimate how much atmospheric CO₂ plants store. All the living mass of plants is just not enough to account for all the carbon dioxide that gets sequestered.

In a recent attempt to reconcile remote-sensing data and carbon field inventories collected from 1992 to 2019, a research team found that terrestrial ecosystems accumulated around 35 gigatonnes of carbon, which amounts to about 30% of human-caused CO₂ emissions. However, only about 1 gigatonne of carbon was stored in living biomass³ (we're glossing over some subtleties in the numbers here to keep this article easy to read, so please visit the original paper in Science to get a complete picture).

Where does the rest go?

Into non-living carbon sinks.

Non-living sinks inherit carbon in the form of dead plant matter, but sequester it away in stable forms (underground, for example) or in anaerobic environments where it doesn't degrade into gases very quickly.

Some of these sinks are natural soils and sediments embedded in grasslands and wetlands, but others are in durable wood products made by humans or even in landfills and under areas flooded by dams.⁴

Stable carbon storage is good news. Living carbon sinks are environmentally sensitive and easy to disrupt. Non-living sinks generally are not.

Think of the huge amounts of carbon re-released into the atmosphere by the fires in Siberia in 2021⁵ or in Canada in 2023.⁶ Not only did the fires release stored carbon: they also prevented the living sink from ever taking up any more.

Non-living carbon sinks are tougher, harder to destroy. They are more stable, and can absorb a lot of carbon in semi-permanent forms.

By understanding more about how non-living carbon sinks work, we should be able to develop long-term carbon storage that is both tough and well-aligned with natural processes.

Every little bit counts, but non-living sinks aren't a "little bit". They are gigatonnes.

Stange, Jamie. "Louder Than Bombs." Beer & Brewing, https://beerandbrewing.com/louder-than-bombs/.
Michael Pollan, “Unhappy Meals,” New York Times, January 28, 2007, https://www.nytimes.com/2007/01/28/magazine/28nutritionism.t.html.
Bar-On, Yinon M., Xiaojun Li, Michael O’Sullivan, Jean-Pierre Wigneron, Stephen Sitch, Philippe Ciais, Christian Frankenberg, and Woodward W. Fischer. “Recent Gains in Global Terrestrial Carbon Stocks Are Mostly Stored in Nonliving Pools.” Science 387, no. 6740 (March 21, 2025): 1291–95. https://doi.org/10.1126/science.adk1637.
Canadell, Josep G. “Looking beyond the Trees for Carbon Storage.” Science 387, no. 6740 (March 21, 2025): 1252–53. https://doi.org/10.1126/science.adw3259.
B. Zheng, P. Ciais, F. Chevallier, H. Yang, J.G. Canadell, Y. Chen, I.R. van der Velde, I. Aben, et al., “Record-high CO₂ emissions from boreal fires in 2021,” Science 379, no. 6635 (2023): 912–917, https://doi.org/10.1126/science.ade0805.
P. Ke, P. Ciais, S. Sitch, W. Li, A. Bastos, et al., “Low Latency Carbon Budget Analysis Reveals a Large Decline of the Land Carbon Sink in 2023,” National Science Review (2024), https://doi.org/10.1093/nsr/nwae367.

Sign up for more like this.