Direct air capture: silver bullet or red herring?

The Committee on Climate Change’s Sixth Carbon Budget is clear that to achieve the UK’s net zero carbon emissions goal by 2050 will require engineering solutions to remove greenhouse gas emissions. Moreover, as the November date for the United Nations’ Climate Change Conference (COP26) in Glasgow draws ever closer, member nations’ will be considering how to capture emissions in their own plans to meet the targets of the Paris Agreement.

Enter direct air carbon capture and storage (DACCS), one of the negative emission technologies (NETs) highlighted by the Sixth Carbon Budget and being trialled around the world. It‘s a simple solution: direct air capture (DAC) technologies use low carbon energy to take carbon dioxide (CO₂) emissions straight from the air for either storage in geological sinks or reuse. But as the technology is in its infancy and unproven at scale, does DAC offer a silver bullet to the climate change conundrum?

DAC technologies remove the CO₂ content from ambient air – effectively, they act as an artificial tree. However, while some of the CO₂ captured by a tree can be released into the atmosphere when it dies, all of the CO₂ captured by DAC can be permanently stored (or re-used). ‘Traditional’ Carbon Capture and Storage (CCS) will capture carbon dioxide from the flue gas of large industrial sources, and can support the generation of energy such as hydrogen; whereas DAC captures carbon dioxide from ambient air. At present, DAC companies are using a process that chemically separates the CO₂ from air[1> – although both cryogenic processes, which freeze the CO₂ out of the air, or membrane technology could be possible alternatives.