Whether by land, by sea, or through human innovation, carbon sequestration is likely coming to (or already happening in) a destination near you. As our planet, overdosed on greenhouse gases, battles climate disasters, a logical solution is to simply stop pumping carbon dioxide into the air. Legislation worldwide is aimed at that target, but reducing output alone may not be enough. There are still billions of tons of extra CO2 already in the atmosphere—this crossroads is where sequestration comes into play.
Carbon sequestration is exactly what it sounds like—the storage of CO2. Once carbon is sucked out of the air, or in some cases pulled directly from industrial smokestacks, sequestration can be undertaken in a lot of different ways. Carbon storage happens naturally, when forests and oceans absorb and convert CO2 into organic matter, but carbon dioxide can also be artificially injected into deep underground rock formations (or wells), or in some cases technological approaches repurpose carbon into a resource like concrete, or as a catalyst in a closed-loop industrial system. However it’s accomplished, the point of sequestration is to stabilize carbon and ensure it doesn’t creep back into our atmosphere. Researchers, like those at the United Nations’ Intergovernmental Panel on Climate Change, now say that CO2 removal is vital to keeping global warming to 1.5 degrees Celsius (past that threshold, climate change could reach catastrophic levels). A 2023 University of Oxford study estimated that, currently, about two billion metric tons of carbon dioxide are being removed each year, primarily through land management (i.e., planting trees), and suggested that we need to double that amount to avoid dangerous global warming levels. Along with recent Environmental Protection Agency (EPA) approvals for class VI injection wells in several states, carbon sequestration is also backed by a $444 million Biden Administration package for large-scale carbon management and infrastructure. Fresh legislation will certainly follow, to hold carbon innovators accountable for yet untested environmental impacts, and some detractors argue that sequestration is unproven and fails to disincentivize off-gassing. Nonetheless, major players around the world, from coastal ecologists in Massachusetts and California startups, to big energy executives and government leaders, are pursuing better carbon storage and view it as a non-negotiable for zero-carbon goals. Ahead, we look at techniques, some familiar and some surprising, for carbon sequestration.
Five If by Land
Forests are well known for their carbon-absorbing capacity, while large-scale farming is more likely to be villainized in today’s environmental discourse. Agriculture, though, is a hotbed for research on carbon sequestration.
More Salt?
Some scientists are proposing the idea of growing biomass crops to capture CO2 from the atmosphere; they would bury the harvested vegetation in engineered dry bio-landfills. With the agro-sequestration process, researchers say that stabilizing the captured carbon is as simple as putting salt on top of the buried debris to halt decomposition, allowing the plants to hang onto captured CO2 for thousands of years.
The BECCS We Can Do
The U.C. Berkeley team behind the biomass-based bioenergy with carbon capture and storage (BECCS) project touts it as a comparatively thrifty option. With BECCS, experts devised a system that captures carbon dioxide produced during the conversion of biomass crops into fuel or energy, permanently sequestering the CO2. The technique is considered one of the few that can potentially be scaled up to the massive volumes needed to make a dent in carbon reduction—and as a bonus it also produces green energy. However, BECCS would likely require tight regulations and thorough oversight to ensure biomasses are sustainably sourced.
Powering Up the Soil
In addition to biomass crops, some startups want to maximize soil’s natural affinity for hanging onto carbon. Andes, a company based in California, developed a microbe-based fertilizer of sorts that causes farmland to absorb higher levels of CO2, and in 2023, it treated 50,000 acres of U.S. land with the product. Similarly, major food industry companies like General Mills and Land O’Lakes have begun paying farmers to embrace regenerative techniques that optimize soil sequestration, such as planting cover crops and moving previous harvest seasons’ “trash” aside rather than tilling it under the soil. Soil-based carbon credits are becoming big business, with some estimates indicating the industry could be worth $50 billion by 2030. Deborah Bossio, the lead soil scientist for the Nature Conservancy, told Science.org that “I and many other scientists have a lot of confidence that we can build carbon in soil.”
Getting to the Roots of a Solution
In another study, farm industry leaders found that grazing dairy farms sequester a substantial amount of carbon, due in part to the grass and their root systems. Canadian researchers are even looking into incentivizing the preservation of the country’s swaths of rural grasslands, because they are such an effective tool for carbon sequestration—as long as they stay intact. The Forest, for the Trees. While farms could be an unexpected success story for carbon sequestration, forests remain an irreplaceable resource, with woodlands in the U.S. Northwest offsetting some 13% of U.S. greenhouse gas emissions. Forestry scientists are examining how to enhance our forests’ carbon sink by carefully timing harvests (which could look like thinning out trees, clear-cutting or even trimming the understory, at the optimal time). Plus, trees can continue holding carbon for up to 80 years after their death, as they slowly decompose. One 2019 study indicated that if the right species of trees are planted, emerging forests could capture 205 gigatons of carbon dioxide in the next 40 to 100 years. Straddling the line between land and sea, coastal habitats (think mangroves and wetlands) also remove a lot of carbon out of the atmosphere, at a rate 10 times greater than mature tropical forests. Researchers at the Smithsonian Environmental Research Center aim to boost the natural abilities of these wetlands by designing methodologies that would award carbon credits to tidal wetland projects.
Looking for a Sea Change
Oceans absorb at least a quarter of the world’s carbon emissions, with some sources putting that number in the 30% to 40% range. Investors are pouring millions into new projects that could further increase that amount. At the Startup Line. Despite questions about the impact of carbon sequestration on marine biodiversity—and how much of the carbon trapped in the ocean would actually stay there—startups are experimenting with creative approaches. Captura wants to remove dissolved CO2 gas from the ocean and pump it underground or reuse it for industrial needs. The company theorizes that shrinking carbon levels in the ocean will allow the bodies of water to absorb more greenhouse gases from the air. In a major deal for ocean-based carbon sequestration, California startup Equatic agreed to remove 62,000 tons of carbon on behalf of Boeing. Equatic’s technology uses an electrolytic process, in which ocean water is split into hydrogen and oxygen; then atmospheric air is run through the processed seawater, in effect stabilizing carbon dioxide permanently in the form of dissolved bicarbonate (in seawater) and solid mineral carbonates. The process also extracts hydrogen as a green energy. If you’ve ever been terrorized by sargassum, the stinky seaweed that has recently washed ashore in the Caribbean and Florida, scientists have a proposal for that aggravation. The National Renewable Energy Laboratory (NREL) conducted a study of several marine carbon management methods, including seaweed farming, microalgae farming, and artificial upwelling (which forces algae bloom by pumping nutrients to the surface from deep in the ocean). They found that though seaweed captures greenhouse gases, it may not store them for long. One potential answer is to sink the seaweed—like that pesky sargassum—deep into the ocean, where carbon could stay sequestered for hundreds of years. Sinking huge clumps of seaweed is not risk-free, though. Sea creatures might make a snack of the marine plants during their downward descent, and researchers don’t know how long the carbon would then remain stored safely away in the belly of a fish. Additionally, swarms of wildlife might gravitate to the seaweed, leading to low-oxygen zones that would kill off more wildlife. There are kinks to be worked out, but one Maine startup, RunningTide, recently signed an agreement with Microsoft to remove 12,000 tons of carbon dioxide via a method that relies on floating kelp; the CO2 is captured in kelp and then sequestered into attached wooden buoys that are sunk into the ocean. A Whale of a Solution? Scientists have even proposed that recovering whale…