Reducing greenhouse gas emissions has become a vital target to prevent a planetary climate crisis. A major hurdle is that practical carbon removal methods are often costly and limited in scale. Two American scientists propose an unconventional solution: using salt to dry and bury biomass. They argue this approach can work and be scalable.
The study, published in the Proceedings of the National Academy of Sciences, argues that their recommendations are necessary because they offer an easy and inexpensive way to store carbon for thousands of years.
The authors describe growing biomass to capture atmospheric carbon, then using salt to maintain dryness and limit microbial activity and decomposition. After harvesting, the vegetation would be buried in specially engineered dry sites designed for this purpose. The researchers emphasize that this could be a practical form of carbon storage.
Eli Yablonovitch, the lead author and a professor at the University of California, Berkeley, calls the result carbon negative and says the approach could be a game changer in the fight against global warming.
He notes that the right engineering could address the climate challenge at a manageable cost. If such a sequestration method were applied globally, not only could current emissions be reduced, but it could also address emissions from earlier years.
In other words, while most efforts focus on reaching zero emissions, the proposed method envisions net negative carbon impact.
The study reports encouraging figures: for each ton of dry biomass, roughly two tons of carbon dioxide could be sequestered.
A technique from the Bronze Age
The idea of embedding biomass to store carbon is not new. It has gained attention in recent years, with groups experimenting with burying various forms of plant matter and even wood in the ground.
The challenge is that even when tanks are made oxygen-free, anaerobic microorganisms can continue to move, breaking biomass into CO2 and methane. This makes some approaches only carbon neutral at best.
California researchers pursued a different path. They began with the assumption that all life, including anaerobic organisms, needs water and moisture.
They found that life processes stall when internal water activity drops below about 60 percent. Living cells require nutrients and water to survive, and a drop below 60 percent can halt metabolism.
How can this be achieved? The scientists turned to an ancient preservation technique: salt. For thousands of years, salting has helped keep food dry and safe.
They claim that their method can securely retain carbon in dry, salted biomass for thousands of years. It is described as lower cost and higher carbon efficiency than many other air capture options.
In addition to long-term stability, the approach could be designed as an agricultural and biological landfill. The authors estimate costs around 54 euros per tonne of CO2 captured, which is far less than several atmospheric CO2 capture strategies in use today.
Biological dumps
A major advantage is that this approach does not require converting land used for food production. Biomass can be grown on marginal grassland, forest land, or fallow fields, making it possible to avoid competing with food crops.
While it may not remove all historic emissions, there is believed to be enough underutilized land to contribute significantly, according to the researchers.
The authors compile a list of more than fifty high-efficiency plant varieties that can thrive in diverse climates while delivering high dry biomass yields and substantial carbon sequestration.
The concept involves salting these plants and burying the dry, engineered biomass in deep, dry landfills that are protected from human activity and natural disasters.
The design draws on practices used in modern landfills, such as adding two nested layers of polyethylene to ensure dryness and stability.
Deckman notes that the approach is technologically ready. Farmers could switch to biomass farming relatively quickly, with an estimated transition time of about a year to convert existing farmland.
The researchers argue that their strategy offers benefits in cost, scalability, and long-term stability. They also say it relies on familiar technologies to provide a practical path for removing carbon dioxide from the atmosphere and addressing climate change.
Still, the scientists acknowledge that society should continue its broader decarbonization efforts, including deploying solar and wind energy and improving energy storage solutions.
A reference report for the study can be found in the PNAS publication.
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