Direct air capture (DAC)
Engineered systems that extract CO2 directly from ambient air using chemical sorbents or solvents, producing a concentrated stream for storage or use.
Atmospheric CO2 is only about 420 ppm (0.042%), roughly 300 times more dilute than coal flue gas, so direct air capture needs large air contactors and substantial energy. Two main approaches exist:
- Liquid solvent (Carbon Engineering / 1PointFive): potassium hydroxide captures CO2; regeneration through calcium carbonate calcination at about 900°C.
- Solid sorbent (Climeworks and others): amine-functionalised filters release CO2 at 80–120°C under low pressure, allowing use of low-grade or waste heat.
Thermodynamic minimum work to separate CO2 from air is about 0.5 GJ/t; real systems run 10–20 times higher. Current costs are USD 500–1,000/t; developers target USD 100–300/t at gigatonne scale. Climeworks' Orca (4,000 t/yr nominal) and Mammoth (36,000 t/yr) plants in Iceland store CO2 by mineralisation in basalt with Carbfix. The US Stratos plant in Texas was designed for 500,000 t/yr.
DAC only reduces net emissions when powered by low-carbon energy; with grid power at 400 g/kWh it would re-emit a large share of the CO2 captured. IEA net-zero pathways assign DAC roughly 1 Gt per year by 2050.
Related terms
All terms →- Carbon capture and storage (CCS)
Technologies that separate CO2 from flue gas or process streams, compress it, and inject it into deep geological formations for permanent storage.
- Net zero
A state in which anthropogenic greenhouse gas emissions are balanced by anthropogenic removals over a specified period, so net additions to the atmosphere are zero.
- Carbon offset
A tradable credit representing one tonne of CO2e reduced, avoided or removed by a project outside the buyer’s own operations, used to compensate for the buyer’s emissions.
- Carbon budget
The cumulative amount of CO2 that can still be emitted while keeping global warming below a given limit with a stated probability.
- E-fuels (power-to-X)
Synthetic fuels made from electrolytic hydrogen, sometimes combined with captured CO2 or nitrogen, such as e-methane, e-methanol, e-kerosene and e-ammonia.