The Buried Potential of Wood Vaults in Achieving Net Zero

The Terrestrial Pathway of carbon dioxide removal (CDR) involves solutions that leverage the natural processes and capabilities of plants, soil, and microorganisms to capture and store carbon out of the atmosphere. Carbon Lockdown, a recipient of Climate Vault’s 2023 Carbon Dioxide Removal Innovation Award, is one such project under the Terrestrial Pathway that is pioneering CDR by collecting sustainably-sourced woody biomass and burying it in a “wood vault” for long-term carbon sequestration. 

In a recent webinar, we sat down with Dr. Ning Zeng, the co-founder and head of science at Carbon Lockdown, and Professor Stephen Pacala, a leading expert in ecology and environmental biology and a member of the Climate Vault Tech Chamber, to learn about the science, technology, and future potential of carbon sequestration through wood burial. Here are the top five takeaways from the conversation:

1. Carbon Removal is Essential for Reaching Net Zero

Carbon removal is a critical component of achieving net zero emissions and mitigating the worst effects of climate change. The fundamental principle behind carbon removal lies in reversing the damage caused by releasing excess CO2, caused by human activities, into the atmosphere. In this way, CDR is a powerful way to mitigate climate impacts and move the planet closer to net-zero emissions. While current technology can mitigate about 80% of our emissions, the remaining 20%—such as emissions from food production—will require active carbon removal to offset. Professor Pacala highlighted the effectiveness of carbon removal strategies, like wood burial, in reversing the climate damage caused by releasing CO2 into the atmosphere, stating, “There’s nothing better when it comes to mitigation than being able to undo what you’ve already started to do.”

The concept of “undoing” climate damage is a powerful one. It reinforces the idea that we not only need to stop adding carbon to the atmosphere but also need to remove what’s already there. This dual approach of reduction and removal is essential in the fight against climate change, especially as we strive to meet international climate goals. Carbon removal strategies are becoming increasingly important as they address historical emissions already in the atmosphere and those that are difficult to eliminate, such as from food production and other essential activities, but the space remains a complex one to navigate. 

2. Wood Burial is Simple & Effective

Wood burial, a method grounded in ecological science, involves burying biomass underground in a controlled, anoxic (oxygen-deprived) environment. The anoxic conditions prevent the wood from decomposing, which means the carbon embodied in the wood is unable to re-enter the atmosphere. Dr. Zeng is credited as the originator of the idea of carbon sequestration via wood burial. According to him, “It’s very simple and requires no new technology. We know how to do this type of civil engineering. The key is to ensure an anoxic condition so that there’s no decomposition.”

The science behind this approach draws on knowledge of carbon cycles and soil microbiology. Plants naturally absorb carbon from the atmosphere via photosynthesis as they grow. Once the plant dies, it begins to decompose, and this process releases the stored carbon back into the atmosphere. While this is a naturally-occurring process, our ability to limit the amount of CO2 that is released back into the atmosphere, such as via wood burial, can help to lower the total amount of CO2 that accumulates in the atmosphere over time. By burying wood in conditions that are low in oxygen and moisture, the decomposition process is significantly slowed, and the carbon remains sequestered within the wood fibers. This method mirrors natural processes seen in peat bogs and other carbon-rich ecosystems, where organic matter is preserved for millennia. According to Professor Pacala, “The fundamental science behind it is really well established and is not really subject to dispute any longer.”

By creating conditions that prevent decomposition, wood burial ensures that the captured carbon remains sequestered for hundreds or even thousands of years. As Dr. Zeng explained, “Nature has already done the difficult job of capturing carbon, and we just need to add some engineering effort to really put the carbon back down.” The simplicity of this method—digging a trench, burying wood, and covering it with clay—is what makes it both effective and scalable. 

3. Wood Vaults are Scalable & Verifiable

Speaking of scalability, this is a major concern for any carbon removal project developer. “As the climate change intensifies, the need for scalable and replicable carbon removal solutions becomes more urgent,” Professor Pacala explained. Both speakers agreed that carbon sequestration via wood vaults offer a scalable and cost-friendly solution to carbon sequestration—with Professor Pacala adding that the benefits of this approach are largely aided by the abundance of available biomass: “The planet produces an extraordinary amount [of wood] in secondary forests that are already harvested and a huge amount of that currently goes to waste.” 

Carbon Lockdown’s approach was also noted as being “entirely verifiable” by Professor Pacala, meaning that the carbon sequestered can be easily measured and verified by opening up the wood vault to find out the state of the wood inside. This type of verifiability is a critical factor for the credibility of any carbon removal project and is crucial for gaining the trust of investors and buyers.  

The ability to implement wood vaults in various locations, coupled with the abundance of available biomass, makes Carbon Lockdown’s method particularly promising. “This technology is scalable and it’s ready now,” stated Professor Pacala. “We don’t have to wait. It’s not a technology that has to be developed a lot in order to start scaling.”

4. The Importance of Site Location

The effectiveness of wood burial as a carbon sequestration method is significantly influenced by the location of the wood vaults. Dr. Zeng explained that the site for the Potomac Project, Carbon Lockdown’s first large-scale wood vault, was chosen based on its suitability for wood burial—specifically, its hydric (water-saturated) soil, proximity to a creek, and unsuitability for growing crops. 

For wood vaults, factors such as soil type, moisture levels, and the potential for disturbances must be carefully considered. The choice of site is critical to ensuring that the buried wood remains undisturbed and that the carbon sequestered remains locked away. Selecting sites with low risk of catastrophic disturbances, such as fire or flooding, is also crucial for the long-term success of terrestrial projects like these. 

By choosing sites that are unsuitable for other uses, such as agriculture in the case of Carbon Lockdown’s Potomac Project site, these projects can also avoid competing with food production while still contributing to climate goals by providing other co-benefits. “The plan [at the Potomac Project] is to bury 5,000 tons of CO2-equivalent of wood in it,” shared Dr. Zeng. “After enclosure, the land above the vault will be re-seeded with plants for pollinator species. And the topography at the surface can be regraded with quite some flexibility to enhance amphibian habitat. The farmer (the land owner) will still even be able to plant winter rye for grazing if he wants.”

5. Addressing Additionality & Leakage

Additionality refers to the principle that a carbon reduction or removal project should provide benefits that would not have occurred without the intervention. For Carbon Lockdown’s wood burial projects, additionality is addressed by ensuring that the wood used is sourced from sustainable forestry practices, where the trees would otherwise be burned or left to decompose, releasing carbon dioxide into the atmosphere. By diverting this wood to a controlled wood burial environment, Carbon Lockdown creates a clear additional carbon benefit that would not have happened in a business-as-usual scenario. 

Leakage, on the other hand, refers to the risk that a carbon sequestration project might indirectly cause an increase in emissions elsewhere. Carbon Lockdown’s wood vault mitigates this risk by carefully managing the entire lifecycle of the wood, from sourcing to burial, and ensuring that the project does not inadvertently lead to deforestation or land-use changes that could negate the carbon benefits. By rigorously addressing both additionality and leakage, Carbon Lockdown is able to demonstrate how wood burial projects are able to provide reliable and verifiable carbon sequestration that contributes meaningfully to climate goals. 

Carbon Lockdown—Ready to Go

Climate Vault’s “Digging into the Terrestrial Pathway with Carbon Lockdown” webinar highlighted the potential of wood burial via wood vault as a scalable, practical, and scientifically sound method for carbon sequestration. With the right conditions and a focus on additionality, leakage, and verifiability, projects like Carbon Lockdown’s could play a significant role in the global effort to combat climate change. As Professor Pacala aptly put it, “Carbon Lockdown is ready to go now, it’s scalable, and some of its competitors may never develop.” 

Want to learn more about Carbon Lockdown and its potential impact on the CDR space? Register to view the webinar-on-demand and hear from Dr. Zeng firsthand about the way wood vaults provide a scalable and cost-effective method backed by science to fight climate change.