Most efforts to address carbon emissions focus on preventing them from entering the atmosphere in the first place. But how to get rid of CO2 already there? Start-ups are developing prototype air-capture systems.
Efforts to combat global warming, triggered and reinforced by rising levels of carbon dioxide as humans burn fossil fuels and convert forests to farmland, largely focus on preventing CO2 from entering the atmosphere in the first place.
But small groups of researchers are pursuing a complementary approach. They are looking for ways to remove CO2 already in the air.
On small scales, the approach has been used since the 1930s at dry-ice facilities, as well as to scrub CO2 from the air on submarines and on the International Space Station. Proposals to use air capture to help reduce atmospheric CO2 concentrations first appeared in 1999.
However, "over the last two or three years, there's been a lot of new [research] publication in this field," says Alain Goeppert, a researcher with the Loker Hydrocarbon Research Institute at the University of Southern California (USC).
The interest is driven in no small part by a handful of start-up firms that are developing prototype air-capture systems. But it's also driven by the recognition that CO2 concentrations in the atmosphere already exceed a level that some scientists say stands the best chance of holding global warming by the end of this century to about 2 degrees Celsius (3.6 degrees Fahrenheit) above preindustrial levels.
Air capture essentially involves passing ambient air across liquid or solid materials that absorb CO2. Conceptually, it's similar to extracting CO2 from coal-fired power-plant emissions.
But air-capture advocates note that some 30 percent of the world's CO2 emissions come from cars, aircraft, and other mobile "nonpoint" sources, where scrubbers at the tailpipe are impractical.