Carbon Capture Technology: Direct Air Capture, CCS, and the Cost Problem

$1,000 Per Ton of CO₂: Why Carbon Removal Costs Must Fall 90%

In 2024, the most advanced commercial direct air capture plant — Climeworks' Mammoth facility in Iceland — could remove carbon dioxide from the atmosphere at a reported cost of approximately $1,000 per ton of CO₂. Current atmospheric CO₂ concentration is approximately 425 parts per million (May 2024), representing about 3.3 trillion tons of anthropogenic excess CO₂ above pre-industrial levels. At $1,000/ton, removing just 1 billion tons annually — less than 3% of current global emissions — would cost $1 trillion per year. The IPCC's AR6 report states that limiting warming to 1.5°C will require removing between 100 and 1,000 billion tons of CO₂ from the atmosphere this century. The cost problem is, at present, almost incomprehensible in scale.

Carbon capture technologies fall into two broad categories: point-source capture (capturing CO₂ at the emission source before it enters the atmosphere) and carbon dioxide removal (CDR, capturing CO₂ from ambient air or oceans). Both are considered necessary components of net-zero pathways by the IPCC, the IEA, and most major climate scenarios.

Point-Source Carbon Capture and Storage (CCS)

Point-source CCS captures CO₂ from concentrated emission sources — power plants, cement factories, steel mills, and hydrogen production facilities — where CO₂ concentration in flue gas is 10–15%, dramatically lower than the 0.04% in ambient air but far more tractable chemically. Three main capture approaches are used:

• Post-combustion capture: CO₂ is separated from flue gas after fuel is burned, typically using amine-based chemical solvents (monoethanolamine is most common). The CO₂-rich solvent is heated to release pure CO₂; the solvent is recycled. This approach can be retrofitted to existing plants.
• Pre-combustion capture: Fuel is converted to hydrogen and CO₂ before combustion. The CO₂ is captured under high pressure, and the hydrogen is burned cleanly. Used in integrated gasification combined cycle (IGCC) plants.
• Oxy-fuel combustion: Fuel is burned in pure oxygen rather than air, producing a flue gas that is mostly CO₂ and water — easy to separate. Requires an air separation unit, adding significant energy cost.

Existing CCS Facilities

The global CCS pipeline as of 2024 includes approximately 41 operational facilities capturing about 49 million tons of CO₂ per year — a tiny fraction of the ~37 billion tons emitted annually. The IEA's Net Zero by 2050 scenario requires CCS capacity to scale to 1.7 billion tons per year by 2030.

Direct Air Capture (DAC)

Direct air capture removes CO₂ directly from the ambient atmosphere, where it exists at only 425 ppm (0.0425%). This dilution makes DAC far more energy-intensive than point-source capture — but DAC can be located anywhere, works regardless of emission source, and can remove historical CO₂ emissions from any emitter anywhere in the world.

• Liquid solvent DAC: Air is passed through a potassium hydroxide solution that absorbs CO₂. The resulting potassium carbonate is processed through a calciner at ~900°C to release pure CO₂ and regenerate the solvent. Carbon Engineering (acquired by Occidental Petroleum in 2023) uses this approach; their Stratos facility in Texas, targeting 500,000 tons/year capacity, began operations in 2024.
• Solid sorbent DAC: Air passes over solid materials (amines or metal-organic frameworks) that bind CO₂ at ambient temperature. Heating releases the CO₂. Lower energy requirement per unit than liquid solvent; used by Climeworks. Mammoth plant in Iceland (2024) targets 36,000 tons/year capture capacity.

Geological Storage: Where the CO₂ Goes

Captured CO₂ must be stored permanently to count as removal. Deep saline aquifers and depleted oil and gas reservoirs are the primary storage options. Geological storage requires:

• Sufficient porosity and permeability in the storage formation to accept large CO₂ volumes
• An impermeable caprock above the storage zone to prevent CO₂ migration
• Long-term monitoring to verify containment (>100 years)

Iceland's basalt geology offers a unique storage option: the Carbfix process reacts CO₂ with basalt to form stable carbonate minerals within 1–2 years, providing permanent solid-phase storage. Climeworks uses Carbfix at its Icelandic facilities. This mineralization approach eliminates long-term leakage risk but requires specific geological conditions not available everywhere.

The Cost Reduction Pathway

The US Inflation Reduction Act (2022) increased the 45Q tax credit for geological CO₂ storage to $85/ton for point-source CCS and $180/ton for DAC — levels that make some projects economically viable for the first time. The EU Innovation Fund and UKRI are providing comparable incentives. Government procurement programs, including the US Department of Energy's $3.5 billion CDR Purchase Pilot Prize, are intended to create early demand while costs fall along a learning curve similar to that observed in solar and battery storage.