Two key steps are crucial to tackling climate change and delivering a healthier planet: 1) emissions reduction and avoidance, and 2) emissions removal.
Although we first and foremost need drastic, radical emissions reductions such as clean electrification, the IPCC makes clear that removing CO₂ from the air, also known as carbon dioxide removal (CDR), is no longer optional if humanity wants to achieve net-zero emissions globally by mid-century, thus limiting global warming to 1.5°C, and eventually go net-negative after 2050. CDR is also referred to as negative emissions to signify the reduction of the absolute concentration of CO₂ in the atmosphere.
This is due to three reasons. First, some sectors like cement production or long-haul aviation are expected to maintain substantial emission levels even post-2050. CDR takes care of these unavoidable emissions, enabling the world as a whole to reach net-zero emissions. Second,in the case of temporary temperature overshoot, meaning that if humanity breaches the remaining carbon budget, additional CDR is needed to bring temperatures below 1.5°C again. Third, the world needs to eventually go net-negative by removing historic emissions post-2050, which will reduce the absolute CO₂ concentration in the atmosphere.
Reducing emissions is crucial, but carbon removal solutions are needed in addition to reach net-zero and eventually net-negative emissions.
Here, we would like to introduce a technological CDR solution: direct air capture and storage (DAC+S). And we will explain how it is different from carbon capture and storage (CCS), since the two terms are often confused with each other.
What is direct air capture and storage?
Direct air capture is a technology that captures carbon dioxide from ambient air. It can be classified as a CDR solution if combined with CO₂ storage. There are many options around the world to store carbon dioxide after it has been captured from the air, making direct air capture a flexible solution that can be situated anywhere in the world.
Climeworks operates the world’s largest DAC+S plant named “Orca” in Iceland. Orca nominally removes 4’000 tons of CO₂ from the atmosphere every year.
Climeworks direct air capture and storage facility 'Orca' in Iceland
The CO₂, which is captured by Orca, is permanently stored underground by turning it into stone with Carbfix’ mineralization approach.
Through the Carbfix process, the air-captured CO₂ from Orca is mixed with water and pumped deep underground, where it mineralizes.
The entire process is powered solely by renewable energy. DAC+S is a scalable solution, which does not compete with arable land, and truly permanent: by storing the captured carbon in basaltic rock formations deep underground, it stays safely stored for millions of years.
To sum up, DAC+S involves two steps:
- Direct air capture: Carbon dioxide is captured from ambient air.
- Permanent storage: The air-captured CO₂ is permanently stored, e.g. via underground mineralization.
What is carbon capture and storage?
Instead of capturing CO₂ from ambient air, carbon capture and storage (CCS) captures it directly from the point sources that produce fossil carbon dioxide, such as the chimneys of existing iron and steel factories. After that, the CO₂ is transported to a storage site, where it is sequestered.
CCS thus involves a three-stage process:
- Carbon capture: Fossil carbon dioxide is captured from a point source.
- Transport: The fossil carbon dioxide is transported to a storage site, because the source of the emissions is typically not located next to a storage site.
- Permanent storage: The carbon dioxide is stored, e.g. by injecting it into rock formations deep underground.
What is the difference between CCS and DAC+S?
CCS is a technology that helps to reduce emissions at the point source because it prevents new fossil CO₂ from entering the atmosphere. DAC+S, on the other hand, is a technology that goes beyond reducing: it removes carbon dioxide from the air, which produces so-called negative emissions. DAC+S allows to remove unavoidable or historic emissions that are already in the atmosphere.
DAC+S removes CO₂ from the air, whereas CCS captures CO₂ from point sources.
Both CCS and DAC+S have an important role to play for the world to reach net-zero emissions, but it’s key to note that they address different parts of our journey towards a net-zero and eventually net-negative world.
Key take-aways
- To stop climate change, we need both emissions reduction and emissions removal.
- Carbon capture & storage (CCS) is an approach that can help to reduce emissions as it captures fossil CO₂ from point sources, preventing it from entering the atmosphere.
- Direct air capture & storage (DAC+S) is a carbon removal solution: it captures CO₂ directly from the air, which is then permanently stored.
- Unlike CCS, DAC+S can produce negative emissions.
- Only by using negative emissions can the world achieve net-zero and eventually net-negative emissions.