Inspired by an ancient buried log, researchers present a novel method to remove and store atmospheric carbon for hundreds of years or more. It involves locking woody biomass away in "wood vaults." The approach could provide a cost-effective solution to mitigate climate change. Achieving net-zero carbon dioxide (CO2) emissions is crucial for combating climate change, yet reducing fossil fuel emissions alone is insufficient to meet the Paris Agreement's targets. To achieve these goals, carbon dioxide removal (CDR) methods must be implemented, including engineering solutions, like direct air capture, and nature-based approaches, such as reforestation or afforestation. Forests play a crucial role in the climate change discourse as significant carbon sinks in natural carbon cycles, sequestering atmospheric carbon through photosynthesis. However, the carbon stored in wood via this natural carbon cycle is often quickly returned to the atmosphere due to decomposition or burning of biomass, leaving little net impact on atmospheric carbon. It is unknown whether carbon-storing woody biomass can be preserved long enough (hundreds of years or longer) to have an appreciable effect on reducing anthropogenic CO2 in the atmosphere. Here, Ning Zeng and colleagues explore the viability of a CDR strategy involving burying sustainably sourced wood in an engineered structure called a "wood vault" to prolong the duration of carbon storage by preventing decay and decomposition. This novel method was inspired by the discovery of a remarkably preserved 3775-year-old Eastern red cedar log buried in clay soil in Quebec, Canada – a find that demonstrates the potential for long-term carbon storage through wood burial within certain environments. By comparing the ancient log to a modern sample from the same species, Zeng et al. found that, despite being buried for nearly 4 millennia, the ancient wood had only lost up to 5% of its carbon, likely due to the low permeability and anoxic nature of the compact clay soil in which it was buried. Using carbon cycle modeling and forestry data, the authors estimate that up to 10 gigatons of CO2 could be sequestered via wood vaulting annually, using trees as well as underutilized wood residues, such as urban tree waste and forest byproducts from commercial thinning. The authors also estimated an initial CDR cost of only $100 to $200 per ton. "A full life-cycle assessment is needed to quantify the net emissions and environmental impacts across ecosystems, supply chains, and engineered wood vaults, as well as to understand how these impacts vary by location and wood sources," writes Yuan Yao in a related Perspective. "These understandings will be critical to developing biomass burial projects on a global scale."
A segment of Science's weekly podcast with Ning Zeng, related to this research, will be available on the Science.org podcast landing page after the embargo lifts. Reporters are free to make use of the segments for broadcast purposes and/or quote from them – with appropriate attribution (i.e., cite "Science podcast"). Please note that the file itself should not be posted to any other Web site.
