Confused about carbon capture? Experts explain why we need different types

The production of steel, concrete, fuel and agriculture chemicals is energy intensive. These industries critically rely on vast amounts of fossil fuels (coal, oil and gas) because the electricity grid doesn’t yet have enough capacity to distribute, store and supply renewables at scale.

Fossil resources are also locked into these industries, with supply chains relying on the chemistry of fossil fuels. During the manufacture of steel, for example, coal is heated without oxygen and converted into coke (another carbon-rich material) – that coke is used in blast furnaces to make molten iron which gets transformed into steel. Therefore, to limit climate change, these industries eventually need to be carbon free. But we do not have the time to make them completely emissions free before global temperatures get any higher.

So what can be done? CO₂ emissions can be captured before they escape into the atmosphere. If that CO₂ is captured, some can be used to make additional products, such as the fizz in beer, sustainable concrete or sustainable fuels for aircraft.

All of this affects us directly in some shape or form, particularly because there have been shortages of CO₂ (due to CO₂ supply relying heavily on fertiliser (ammonia) and bioethanol plants). As fossil fuels become more expensive, these sources become uneconomical to run and production shuts down. Recent global conflicts have also stalled the delivery of liquefied natural gas (LNG), further compounding rising energy costs.

As for the rest of the CO₂, it needs to be stored securely. There is simply too much of it to use and letting even more greenhouse gas emissions escape into the atmosphere contributes to climate change. This whole process is known as carbon capture, utilisation (use) and storage (CCUS).

The CO₂ from industry is removed before it’s emitted, and a small amount of captured CO₂ is used by other industries that rely on CO₂ as a product, then the rest is stored permanently. Using renewable energy to capture the CO₂ avoids further emissions during the capture process.

Unfortunately, CCUS alone is not enough. There are currently around 77 facilities operating worldwide which capture and store or “geostore” CO₂ in rocks underground and in former oil and gas fields. This only accounts for about 0.01% of humanity’s emissions. The processes are expensive and require huge investments from governments or private companies, so it’s hard to scale. Facility costs vary wildly depending on the capture technology, transport and storage option, but lie roughly between US$300 million (£224 million) to US$1 billion.

CCUS facilities simply cannot capture the huge scale of CO₂ in these critical industries all the time, everywhere. Even if industry emissions were capped, that only limits current emissions. Past emissions of CO₂ are still in the atmosphere, so capture of CO₂ directly from the atmosphere is critical.

There is another form of carbon capture, but with a different source of CO₂ – the legacy of burning fossil fuels for more than 260 years since the industrial revolution began. This is known as carbon dioxide removal (CDR) and includes direct air capture which strips the CO₂ from the atmosphere.

Once again, renewable energy is needed to power this process. Another CDR approach is carbon mineralisation in which CO₂ along with water is injected into basalt and similar rocks, then the CO₂ reacts with calcium and magnesium in this water to form solid minerals, rather like the limescale that forms in kettles.

Understanding the difference between these very important approaches enables governments, industries and research funders to know when and where to use them. Time is short. Global temperatures continue to rise. Industrial and domestic decarbonisation needs to progress in parallel with the remedial processes of carbon capture, its use, and removal.