Carbon capture is likely to play a role in the path to net zero emissions – although debate rages as to how big that role should be.
But what should be done with the carbon once it’s captured? While it can be stored underground, it’s also possible to put the carbon to another use once captured, in building materials, industrial chemicals, or as a fuel that re-enters the atmosphere.
This is called carbon capture and utilisation (CCU), and unfortunately – according to a study in One Earth – most initiatives are unlikely to help us reach the Paris Agreement targets.
“It sounds really good, right?” says lead author Kiane de Kleijne, a climate researcher at Radboud University, the Netherlands.
“It’s taking problematic waste and turning it into a valuable product. But we assessed and harmonised many previous studies on CCU, and this showed us that CCU doesn’t consistently reduce emissions.”
The researchers investigated 74 different methods of CCU, considering the sources (whether capturing emissions from mining sites or power plants, or sucking carbon directly from the atmosphere), through to conversion, usage and lifetime of the carbon product.
Many of the capture and conversion technologies are very energy intensive, and some of the final products don’t store carbon for a long period of time – if it’s being converted to methane or methanol to be re-used as a fuel, for instance, it could re-enter the atmosphere in days.
The researchers assessed each of these methods against the Paris target of net zero emissions by 2050, and the Paris-compatible target of halving 2020 emissions by 2030.
Only eight of the 74 methods could reduce emissions significantly enough to meet 2030 goals, and just four were compatible with a net zero by 2050 target.
De Kleijne says that the handful of 2050-compatible routes are promising. Of particular interest is using captured CO2 to make steel slag for construction purposes, which would lock the carbon away for centuries.
But, in their paper, the researchers emphasise that this carbon dioxide would need to be removed directly from the atmosphere or from biogenic sources (plants and animals respiring CO2), and all of the energy involved in this capture and conversion would need to be zero emissions.
The researchers conclude that, while CCU has some potential, it shouldn’t be treated as a mature technology or a monolithic way of reducing emissions.
“We recommend that decision-makers recognise this diversity in CCU, base their decisions on the share of emissions an individual CCU technology can reduce, and whether (close to) zero emissions or [carbon dioxide removal] can be achieved rather than treating CCU as a homogeneous technology,” they write in their paper.
“If a technology is not going to reduce emissions by a lot and it’s still very far away from commercialisation, then maybe it is better to redirect funding to technologies that do have the potential of really drastically reducing emissions,” says de Kleijne.