Pulling CO2 from the air: promising idea, big price tag

The Institution of Mechanical Engineers estimates that it could take as many as 10 million air-capture devices sucking up one metric ton of CO2 per day to absorb just 3.6 billion tons - about one-tenth of current global emissions. The costs of deploying these devices could be staggering. Climatologist James Hansen estimates it would cost roughly $20 trillion per 50 ppm of CO2 removed.

“It’s on the scale of the global military effort,” the Carnegie Institution’s Caldeira says. “The tragedy is there’s no reason to be considering these options at all if we could just learn to cooperate [on reducing emissions], but the evidence that we are learning to co-operate is not very strong.”

Still, Lackner remains undeterred. By the end of the year, he hopes to have a small demonstration of his resin-based artificial tree - looking more like a mobile home with a large pinwheel on top - running at Columbia University. Physicist David Keith of the University of Calgary will launch his air capture company, which uses amines to extract CO2, in October.

“If we had lots of money and things went really well, we could build a pilot plant in five years,” Keith says. “I’m not saying we will be. This field is filled with people’s overconfidence.”

The Royal Society’s Shepherd said that, given the expense of air capture technology, “the first line of defence would be carbon capture and storage and taking it out at the point of emission”. But air capture could be effective in offsetting emissions from sources such as airlines, Shepherd said.

The challenges - and expense - of air capture also serve as a stark reminder to policy makers that the best tactic for combating climate change is to pursue energy efficiency and renewable energy programs and avoid emitting CO2 in the first place. As the Royal Society report notes: “The safest and most predictable method of moderating climate change is to take early and effective action to reduce emissions of greenhouse gases. No geoengineering method can provide an easy or readily acceptable alternative solution to the problem of climate change.”

Not even artificial trees.