Hope for CO₂ air capture

John Tanner’s summary of carbon dioxide air-capture costs (Physics Today, February 2023, page 12 ) takes the glass-half-empty approach to an extreme. At the average US retail price for electricity (12¢/kWh), the thermodynamic energy demand of direct air capture ¹ would indeed add $15 to the cost of collecting a metric ton of CO₂ from air. But large power consumers, such as aluminum smelters, get much better pricing. ²

Moreover, removing 8 billion metric tons of CO₂ for a mere $120 billion would be a good deal. It would cancel past emissions from about 20 billion barrels of oil. The world buys that much oil every 200 days for $1.6 trillion. Prices for such a quantity have fluctuated between $200 billion and $3 trillion over the years. The implied surcharge of $6 per barrel seems cheap for fixing the climate.

Can air capture achieve such economics? The bad news is that current costs are above $500 per metric ton of CO₂. I agree with Tanner that thermodynamic limits plus unavoidable raw-material inputs set a lower bound around $10–$20 per metric ton. ³ The good news is that no physical law prevents approaching that bound through learning by doing. Betting against an order-of-magnitude cost reduction ignores the two-orders-of-magnitude reduction in wind and solar. It collides with the frequently expressed optimism that batteries will get cheaper if we produce a lot of them. Mass production has proven over and over that costs can drop 10-fold if cumulative capacity increases 1000-fold. ⁴ For air capture, which needs to grow more than a millionfold, that represents just the beginning of the growth curve. ⁵ Obviously, success is not guaranteed, but closing the door to the opportunity without trying is self-defeating.