Working at the Los Alamos National Laboratory during the 1990s, Klaus Lackner had numerous interests: the behavior of high explosives, nuclear fusion, and self-replicating machine systems. At some point, he turned his attention to the technology used to capture CO2 from the smokestacks of coal plants — technology in which the U.S. government has invested billions of dollars, with little to show for it. He began to wonder whether it might make more sense to scrub CO2 from the atmosphere. So when his daughter Claire asked for help with a science project, he asked her: “Why don’t you pull CO2 out of the air?”

Chemical engineers have known for decades that sodium hydroxide, a caustic base also known as lye, will bind with CO2, an acid, to make carbonates. That’s basically how CO2 is removed from the air so people can continue to breathe on submarines or in spaceships. Claire accomplished the feat by filling a test tube with a solution of sodium hydroxide, buying a fish-tank pump from a pet store, and running air through the test tube all night. By the next day, some of the sodium hydroxide had absorbed CO2, creating a solution of sodium carbonate.

“I was surprised that she pulled this off as well as she did,” Lackner recalls, “which made me feel that it could be easier than I thought.”

Duly inspired, Lackner set off on a quest to design a machine to pull CO2 out of the air. This would seem to be much harder than collecting carbon dioxide from the smokestacks of power plants that burn coal or natural gas, where concentrations of CO2 are about 12 percent (for coal) or 4 percent (for natural gas). Less than 0.04 percent of the air is CO2. Still, in a presentation called “Carbon Dioxide Extraction From Air: Is It An Option?” that he wrote in 1999 with Hans-Joachim Ziock, a colleague at Los Alamos, and the late Patrick Grimes, an expert in chemical processes, Lackner identified an important role for air-capture technology:

While it may be cost-advantageous to collect the carbon dioxide at concentrated sources without ever letting it enter the atmosphere, this approach is not available for the many diffuse sources of carbon dioxide. Similarly, for many older plants a retrofit to collect the carbon dioxide is either impossible or prohibitively expensive. For these cases we investigate the possibility of collecting the carbon dioxide directly from the atmosphere. We conclude that there are no fundamental obstacles to this approach and that it deserves further investigation.

This remains key to the appeal of air capture: Because greenhouse gases are dispersed around the globe, they can be extracted from the air anywhere. Carbon dioxide spewing from a tailpipe in Sao Paulo or a coal plant in China can be captured by a machine in Iceland or the Middle East, because the atmosphere functions as a conveyor belt, moving CO2 from its sources to any sink. That’s important, because while we can envision a world where most or all of the electricity we use comes from nuclear, solar, or wind energy, or from fossil fuels where the CO2 is captured at the power plant, it’s harder to see how emissions from cars, trucks, trains, ships, and planes can be eliminated. The beauty of air capture, Lackner and his colleagues explained, is that “one could collect CO2 after the fact and from any source … One would not have to wait for the phasing out of existing infrastructure before addressing the greenhouse gas problem.” Air capture plants, they wrote, could be located atop the best underground reservoirs for storing CO2, which may be in isolated locations. This fact is key to the business plans of all the air-capture start-ups. In only one regard was Lackner’s paper clearly mistaken — he estimated that the cost of air capture would be “on the order of $10 to $15 per ton,” a target that now looks wildly optimistic.