Environment: Removing carbon dioxide directly from the atmosphere could help combat climate change. Will it really work?
Preventing catastrophic climate change, most people agree, will mean reducing the level of man-made carbon dioxide (CO2) in the atmosphere. That, in turn, will require the widespread use of “low carbon” technologies such as solar and wind power, more energy-efficient buildings, and so on. Some countries have pledged to reduce their greenhouse-gas emissions by 80% by 2050, and campaigners are calling for cuts of 90% or even 100%. New Zealand, Costa Rica and Norway are racing to become the world's first “carbon neutral” country. But some researchers think there might be a simpler way to reduce the level of CO2 in the atmosphere: to build “air capture” machines that, as their name suggests, grab it from the air.
This is not as mad as it sounds. After all, such machines already exist. they are used to “scrub” carbon dioxide from the air on board submarines and spacecraft. “It has been around for decades, but the only people who cared were at NASA, because too much CO2 in a space shuttle means you die,” says Matthew Eisaman, a researcher at the Palo Alto Research Centre (PARC) in California. Proponents of air capture propose scaling up such machinery so that it can process the atmosphere directly, extracting the CO2 so that it can be sold for industrial use or stored underground.
In some respects this is a more ambitious version of the “carbon capture and sequestration” (CCS) technology that is being developed to strip carbon dioxide from the exhaust gases produced by coal- and gas-fired power stations. The exhaust from a coal-fired power station is around 10% carbon dioxide, however, whereas the level in the atmosphere is a mere 0.04%. But scientists working on air capture suggest that this difference is not as significant as it may seem, and that the kinds of industrial methods needed to strip CO2 from the air have already been proven in industrial processes such as papermaking.
Air capture has the further advantage that it can be done anywhere, not just in places where carbon dioxide is being emitted, such as power stations. An air-capture plant could, for example, be set up at a site where CO2 can be easily stored, such as an empty oilfield, and air capture would open the way to capturing emissions produced by millions of cars and aircraft.
If air capture is to get anywhere, however, it must overcome three sets of objections: technical, financial and political. The process is no good if it produces more carbon-dioxide emissions than it removes from the atmosphere. Nor is it of any practical value unless the cost of removing each ton of CO2 is lower than the alternatives. And whether or not it can be made to work efficiently and cheaply, air capture will be politically controversial because the mere possibility of its deployment could be used as an excuse to put off other action to reduce emissions.