Direct Air Capture Capacity Triples as Climeworks Opens Mammoth II and Heirloom Cuts Costs Below $400 Per Ton

📋 Climeworks Doubles Down on Iceland

Climeworks, the Swiss pioneer of direct air capture technology, inaugurated its Mammoth II facility on May 22, 2026, at the Hellisheiði geothermal park in Iceland. The plant captures 72,000 metric tons of carbon dioxide from ambient air per year, tripling the capacity of the original Mammoth plant (36,000 tons/year) that started operations in May 2024. The CO2 is dissolved in water and injected into basaltic rock formations 700 meters underground by Climeworks' partner Carbfix, where it mineralizes into stable carbonate rock within approximately two years, achieving permanent geological storage.

The plant uses Climeworks' third-generation modular collector technology: each collector unit contains a solid sorbent filter material based on amine-functionalized cellulose that selectively binds CO2 from ambient air at approximately 420 ppm concentration. When saturated, the collector closes, and low-grade geothermal heat at approximately 100 degrees Celsius drives off the pure CO2 for collection.

The Hellisheiði site is co-located with ON Power's geothermal plant, providing renewable electricity and waste heat, which is essential because the thermal energy required to regenerate the sorbent constitutes roughly 70% of the plant's operating cost. Climeworks estimates the Mammoth II plant's capture cost at approximately $550 per ton, targeting below $300 per ton by 2030 through sorbent material improvements and manufacturing scale.

💡 Heirloom Carbon's Cost Breakthrough

Heirloom Carbon, a San Francisco-based startup founded in 2020 and backed by Breakthrough Energy Ventures, Microsoft's Climate Innovation Fund, and Carbon Direct, achieved a milestone in May 2026 by demonstrating a capture cost of $385 per ton of CO2 at pilot scale, down from approximately $1,000 per ton in 2023. Heirloom's approach eschews fan-driven collectors and solid sorbents in favor of a limestone-based cyclic process that takes advantage of the natural carbonation of calcium oxide.

Limestone (calcium carbonate) is heated in an electric kiln to produce calcium oxide (quicklime), releasing one molecule of CO2 per CaCO3 decomposed in a pure stream that can be captured. The calcium oxide is then spread in thin layers on vertically stacked trays exposed to ambient air, where it spontaneously reacts with atmospheric CO2 to reform calcium carbonate over approximately three days, completing the cycle.

Heirloom's cost reduction has been driven by process engineering rather than sorbent chemistry innovations: electric kilns running on a combination of solar and wind power eliminate the need for fossil fuel combustion, and the passive air contact design avoids the fan electricity that accounts for 25-30% of energy use in collector-based DAC systems. A partnership with CarbonCure Technologies injects the captured CO2 into fresh concrete, where it mineralizes and permanently strengthens the material, providing a near-term revenue pathway and avoiding the need for geological storage infrastructure.

The company aims to reach $200/ton by 2030 and projects a total addressable market measured in billions of tons per year if costs reach the $100/ton level that the IPCC has identified as economically viable for most emissions mitigation strategies.

📈 US Government Commitment and Market Realities

The US Department of Energy's Regional Direct Air Capture Hubs program, funded by the Bipartisan Infrastructure Law, awarded $3.5 billion in grants to two commercial-scale DAC hub projects. The first, Project Cypress in Louisiana, is a consortium led by Battelle, Climeworks, and Heirloom targeting 1 million tons per year capture capacity by 2030 with geological storage in saline aquifers. The second, the California DAC Hub led by the California Resources Corporation with Carbon Engineering as technology provider, targets 500,000 tons per year by 2028 with some CO2 used for enhanced oil recovery.

Carbon Engineering's Stratos plant, under construction in the Permian Basin of Texas and backed by Occidental Petroleum's 1PointFive subsidiary, is on track for a 2027 startup at a capacity of 250,000 tons per year, or potentially 500,000 tons in a planned second phase. Stratos uses a liquid-solvent-based capture system (potassium hydroxide solution) with calcination regeneration, a different technology from the solid sorbent and limestone approaches, and will leverage Occidental's expertise in CO2 handling and geological storage.

The plant is estimated to cost approximately $1.1 billion, or about $4,400 per ton-year of capacity, a figure that needs to fall to roughly $1,000 per ton-year for unsubsidized economic viability. The voluntary carbon market provides a bridge: Microsoft, Stripe, and Shopify are purchasing DAC credits at $800-1,200 per ton through the Frontier buyers' coalition, providing early revenue that helps companies move down the cost curve while meeting corporate net-zero commitments.