Pathway-101

Mineralization is the family of carbon dioxide removal (CDR) approaches that convert CO₂ into solid carbonate minerals — the same calcium and magnesium carbonates that make up limestone and dolomite. Once CO₂ is bonded into a carbonate lattice, it is thermodynamically stable on geological timescales, which is why mineralization sits at the durable end of the CDR spectrum alongside geologic injection. The pathway matters because it offers storage that does not depend on monitored plumes, biological uptake, or intact ecosystems — and because the reactive feedstocks (basalt, peridotite, olivine, steel slag, cement kiln dust, mine tailings, alkaline ash) are already abundant, often as waste streams. ...

Afforestation, reforestation and the wider “land sink” bucket Afforestation — planting trees where there were none in recent history — and its close cousin reforestation (replanting where forest was recently cleared) remain the largest single category of carbon removal sold today, by both tonnes issued and dollars transacted. The pitch is straightforward: trees pull CO₂ out of the air through photosynthesis and lock a fraction of it into wood, roots and soil organic matter for as long as the forest stands. The complications are equally straightforward: forests burn, get cut, get sick, and the carbon goes back. For a senior buyer comparing pathways, the central question is not whether trees sequester carbon — they obviously do — but how durable, additional and well-measured a given project actually is, and how that compares to engineered alternatives at 10–100× the price per tonne. ...

What BECCS is, and why it’s in the durable-CDR conversation Bioenergy with carbon capture and storage (BECCS) is the simple-sounding idea of growing plants (which pull CO₂ out of the air via photosynthesis), using that biomass to produce energy or fuel, capturing the CO₂ released when the biomass is processed, and putting that CO₂ somewhere it won’t come back out — almost always a deep saline aquifer or depleted hydrocarbon reservoir. The net result, if the accounting holds, is atmospheric CO₂ removed and geologically stored on the order of 10,000+ years. ...

What “Ocean CDR” actually means Ocean carbon dioxide removal is a family of techniques that use the sea — the planet’s largest active carbon reservoir, holding roughly 50 times more carbon than the atmosphere — to draw down atmospheric CO₂ and keep it down. The ocean already absorbs about a quarter of annual anthropogenic emissions through air-sea gas exchange (Friedlingstein et al., 2023). Ocean CDR approaches either accelerate that natural uptake (by shifting seawater chemistry) or use biology to fix carbon and export it below the mixed layer, where it stays out of atmospheric contact for centuries to millennia. The appeal for buyers chasing durable removal is straightforward: the storage reservoir is enormous, and the residence times — particularly for bicarbonate ion in the deep ocean — are on the order of 10,000 years (Siegel et al., 2021). ...

What “soil carbon” means in a CDR context Soil carbon as a removal pathway is the deliberate addition — or protection — of organic carbon in agricultural and grassland soils so that atmospheric CO₂ ends up stored as soil organic matter rather than circulating in the air. In practice, almost every commercial project in the directory today is doing this through biochar: pyrolysing biomass into a stable, carbon-rich solid and burying it in farmland. A smaller share of projects pursue management-based sequestration (cover crops, no-till, compost, agroforestry) where the carbon gain comes from shifting the balance between plant input and microbial decomposition. The two approaches share a destination — carbon in soil — but the durability profiles and the science behind them are very different, which is the single most important thing for a buyer or journalist to internalise before going further. ...

Direct Air Capture (DAC) is the use of engineered equipment — fans, sorbents, solvents, or electrochemical cells — to separate carbon dioxide from ambient air, concentrate it, and hand it off to either permanent storage or industrial use. Unlike point-source capture at a power plant or cement kiln, DAC has no flue gas to draw from: it works against an atmospheric concentration of roughly 425 ppm, which is the central reason it is both energy-intensive and, when paired with geological storage, one of the most durable carbon dioxide removal (CDR) options available. For buyers and policymakers building portfolios with century-plus permanence, DAC sits alongside mineralization and bio-oil sequestration as a small-but-growing share of the durable removals market. ...

The pathway Enhanced weathering (EW) accelerates a chemical reaction that the Earth already runs at geological pace: the dissolution of silicate rocks by carbonic acid in rainwater. When fast-weathering rocks like basalt, olivine, or wollastonite are crushed to fine particles and spread — usually on cropland, sometimes in rivers, forests, or mine pits — the surface area available for reaction increases by orders of magnitude. CO₂ dissolved in soil water reacts with the minerals, producing dissolved bicarbonate ions that drain through soils to groundwater and eventually the ocean, where the carbon is stored on timescales of 10,000 to 100,000+ years. That long-tailed durability is why EW sits alongside direct air capture and mineralization in most “durable CDR” portfolios, even though it borrows infrastructure (quarries, ag spreaders) from existing industries. ...

Biochar: the pathway Biochar is what you get when you cook biomass — crop residues, forestry waste, sewage sludge — in a low-oxygen environment at several hundred degrees Celsius. The carbon that the plant pulled out of the atmosphere ends up locked in a stable, ring-structured solid that resists microbial decay for centuries when applied to soil or used as a filler in concrete and asphalt. It is, by volume, the largest delivered carbon dioxide removal (CDR) pathway today: biochar accounts for the majority of tonnes actually issued on registries like Puro.earth and the European Biochar Certificate (EBC), even as direct air capture attracts more capital per tonne announced. ...

The premise Biomass burial is the deliberate placement of plant matter — wood chips, agricultural residues, sludges, algae, even whole logs — into an environment where it cannot decompose. The carbon a tree pulled from the air over its lifetime stays as carbon, instead of returning to the atmosphere as CO₂ or methane within years or decades. The appeal is that the hard part of carbon removal — pulling CO₂ out of dilute air — has already been done, for free, by photosynthesis. The engineering problem is narrower: stop the rot. ...