Introduction to Direct Air Capture

The atmosphere contains 3,200 gigatons of CO₂, and we add 40 gigatons annually. Cutting emissions to zero is necessary but insufficient—we've already emitted too much. IPCC pathways limiting warming to 1.5°C require removing 6-10 gigatons CO₂/year by 2050. Direct Air Capture (DAC) pulls CO₂ directly from ambient air (420 ppm concentration) using chemical processes, then stores it permanently underground or converts it to products. Unlike point-source capture (power plants, cement factories), DAC works anywhere and addresses legacy emissions. The physics are brutal: CO₂ is dilute in air (0.042%), requiring enormous air throughput. A 1 Mt/year DAC plant must process 24 billion cubic meters of air annually—equivalent to the volume of 10,000 Empire State Buildings. Two technology approaches dominate: Liquid solvent systems (amine-based) and solid sorbent systems (temperature-swing or moisture-swing). Both require significant energy (1.5-2.5 MWh per ton CO₂) for capture and regeneration. Current capacity is tiny: Global DAC removes ~10,000 tons CO₂/year (0.01 megatons). Climeworks' Orca plant in Iceland captures 4,000 t/year. Carbon Engineering's pilot in Canada captures 1 t/day. To hit 2050 targets, we need 10,000x scale-up in 25 years—comparable to deploying solar/wind but for a technology still in its infancy.