While carbon removal is actually nothing new (plants, the ocean, soils have been absorbing carbon from the atmosphere and storing it throughout time), the emergence of carbon removal technologies as a tool to help restore our climate has put the topic of carbon removal - along with a flood of related terms - in the news with greater frequency these days. Terms like “carbon capture and sequestration” and “carbon removal” and “direct air capture” can be confusing, and the contrast with conventional carbon offsets further complicates the conversation. Here are a few definitions to help.
- Carbon capture refers to capturing carbon dioxide emissions at the source, at industrial power plants. Carbon capture removes new carbon emissions.
- Sequestration is the term often used alongside carbon capture to describe how the carbon dioxide is stored. Carbon sequestration can be geologic (e.g. in underground geologic formations) or biologic (e.g. in plants, soils, wood and wood products, and aquatic environments).
- Direct air capture removes past carbon emissions - carbon that has already been emitted into the environment. Direct air capture is different than carbon capture because it takes carbon dioxide from the ambient air verus from an industrial flue stream. This means that CO2 that has built up in the atmosphere is cleaned up through direct air capture, in contrast to removing new emissions from an industrial process. While direct air capture is not yet widespread (there are 15 operational direct air capture plants in the world), it is recognized as one of of few technology options available to help remove CO2 from the atmosphere quickly.
Both direct air capture and carbon capture can be combined with geologic storage (sequestration).
- In the case of Tomorrow’s Air partner Climeworks, which provides direct air capture with permanent storage, carbon dioxide is stored deep underground in porous basaltic rock (in the case of Iceland) or in peridotite (in Oman). The carbon dioxide collected from the atmosphere is dissolved in water prior to being put in the ground. This makes it dense and therefore it sinks; it is not near the surface. The reactions between the CO2 and the basaltic rocks are fast and once carbon dioxide is transformed into stone (mineralized) no weather conditions or fire can harm it or cause a release of carbon dioxide.
- Carbon capture and sequestration is often discussed in context with ‘enhanced oil recovery,’ the process is used to help extract more oil from wells that have been mostly depleted. When liquid carbon dioxide is injected into the geologic formation that held the oil, remaining oil is less dense, and floats to the top, permitting the oil well to be more productive.
In summary, removing CO2 from an industrial process ( new emissions) and removing CO2 existing in the atmosphere (legacy emissions) are different. It is important to understand that removing legacy emissions is necessary because Earth’s atmosphere now contains so much CO2 that even if all emissions halted today, we still have tons and tons of carbon dioxide to clean up. In fact, the Intergovernmental Panel on Climate Change’s (IPCC) 2018 report has said that in order to limit global warming we need to remove 100 - 1000 gigatons of carbon dioxide from the atmosphere over the 21st century. The National Academies of Science and Medicine advises “removing ~10 Gt/yr CO2 globally” by midcentury. Trying to get a sense of the scale is daunting. To visualize one gigaton imagine one billion metric tons or 2.2 trillion pounds, or 10,000 fully-loaded U.S. aircraft carriers.
The reality is that we now have so much CO2 built up in the atmosphere, natural systems alone can’t handle it all fast enough. Through Tomorrow’s Air, travelers and travel businesses can help spread the word about carbon removal technologies and remove and permanently store carbon themselves, too.
Helpful videos on carbon removal:
Joe Hezir presentation at Carnegie Mellon
National Academies of Science
Climeworks 44.01 partnership