Linus Hofstetter

The world is headed on a gradual journey towards net zero carbon emissions, one potentially big player in reaching this goal are negative emissions technologies. They might even turn out to be our most important tool in preventing the devastating consequences of climate change and are heavily endorsed in the most recent IPCC report and by experts all around the world. But what technologies are already available and are they capable of saving the world?

There are many forms of negative emissions technologies (NET) and a wide variety of ideas on how and where to capture and store carbon, but while NETs are developing at a fast pace, they still have a long way to go until extensive implementation(Royal Society of Chemistry, 2022). Two of the most discussed methods are capture and storage in Biomass, and direct carbon capture from the air.

Afforestation and reforestation

Afforestation describes the process of establishing forest in an area that has not previously been under tree coverage, reforestation is recultivating recently deforested areas with new trees. Capturing excess carbon in Biomass trough photosynthesis is a trivial, but relevant way of negative emissions. It has the huge advantage to be independent of new technologies or complex infrastructure and external power, but it does need gigantic areas of forest per ton of captured CO2 compared to other NETs(Erans et al., 2022). Under optimal conditions during the first 20 years of growth, a forest can store up to 10 kg of CO2 per m2 per year, but under normal circumstances this number turns out to be much smaller and is highly dependent on the type of forest in question(Bernal et al., 2018; US. Environmental Protection Agency, 2012).

Furthermore, the changes in albedo that come with covering new areas with forest can have counterproductive effects on the global climate, especially when affecting areas often covered in snow. The long-term storage of captured carbon poses another problem since it is released back into the atmosphere as soon as the tree that captured it starts to decompose. Re- and Afforestation are most effective on fertile soil which causes a conflict between them and agricultural needs that are increasingly threatened by soil degradation(Bernal et al., 2018; Erans et al., 2022).

Direct air capture (DAC)

One of the most researched approaches to reach negative emissions, is extracting carbon directly from the air and letting it mineralize underground or selling it and processing it further. This is exactly what companies like Carbon Engineering, 1pointfive or the swiss company Climeworks are trying to achieve. To do this, air is pulled through a high surface area PVC packing system and the CO2 reacts with an alkaline solution flowing through it, forming a carbonate salt. This salt is isolated and pure CO2 is extracted again via heating; all reactants are directly recycled on site(1pointfive, 2022; Climeworks, 2021; Carbon Engeneering Ltd., 2022). According to Climeworks, s single Collector has the capacity to capture as much CO2 as 2000 Trees, on a fraction of the area and its installation speed isn’t limited by biomass accumulation speed(Climeworks, 2021; Carbon Engeneering Ltd., 2022).

Direct carbon capture aims to accelerate global emissions reduction, while enabling net zero emissions by addressing carbon, emitted over the last decades. Considering this, direct air capture is a complementary technology to carbon capture and storage (CCS), which aims to capture emissions right at the source. Some industries cause decentralized emissions and are harder to decarbonize, like for example small vehicles or planes. Direct air capture can help compensate their emissions. Since CCS mostly operates under high concentrations of not only CO2, but also SO2 and NOx, its performance and lifespan can be significantly worse than it is with direct air capture facilities(van Egmond & Hekkert, 2012).

Direct air capture has many problems to overcome to be a relevant contributor in getting to net zero emissions. At the moment it is just not an economically viable option to mitigating climate change(Socolow et al., 2011). In contrast to renewable energy, direct air capture generates no direct monetary value, but has considerable costs in installation and maintenance. Costs per ton of captured CO2 are estimated to be at 1000 US dollars minimally, whereas capturing the same amount of CO2 today through CCS at the source of centralized emitters, costs around 10 US dollars. Companies involved in direct carbon capture claim to being able to reach prices of under 100 US dollars per captured ton of CO2 soon, but the feasibility remains unclear(Socolow et al., 2011).

As many other local solutions tackling global problems, direct carbon capture is victim to a tragedy of the commons. Everyone benefits from low CO2 concentrations in our atmosphere, but free riders profit just as much from NETs as investors, without carrying their cost. Another potential hurdle to overcome is public acceptance. As of today, most people have yet to form an opinion concerning direct air capture, which makes it hard to predict how the public opinion on this technology will look like in the future. But since direct carbon capture can hardly be self-sustaining financially, it will most likely be heavily dependent on public funding which is much harder to get without public acceptance(Erans et al., 2022; Gbrielli et al., 2020; Royal society of chemistry, 2022).

With NETs comes the danger of policies and other decisions to rely on future technologies that may promise more than they can deliver. The fact that we might be able to effectively filter carbon out of the atmosphere, should and can not be used to justify delaying other measures combating climate change(Socolow et al., 2011).

So what?

What we can conclude is, that NETs are complementary technologies to conventional decarbonization and climate change mitigation options, not a substitute. Direct carbon capture and organic carbon fixation via trees might turn out to be highly important in the future and should certainly be researched further, but today, they fall short on too many important aspects in comparison to other methods reducing emissions. As long as centralized sources with emissions of highly concentrated CO2 exist, local carbon capture installed directly in emitters is cheaper, more efficient and tackles the problem at the source. Re- and Afforestation are slow and high effort. They constitute one small part of the solution, but preventing deforestation remains cheaper, faster, and easier to implement. What we learn from those examples is, that prevention should always be the first step and if we have our positive emissions in check, NETs are hopefully ready to deal with the rest.

References

1pointfive. (2022). DAC Technology | 1PointFive. https://www.1pointfive.com/dac-technology

Bernal, B., Murray, L. T., & Pearson, T. R. H. (2018). Global carbon dioxide removal rates from forest landscape restoration activities. Carbon Balance and Management, 13(1), 1–13. https://doi.org/10.1186/S13021-018-0110-8/FIGURES/4

Carbon Engeneering Ltd. (2022). Direct Air Capture Technology | Carbon Engineering. https://carbonengineering.com/our-technology/

Climeworks. (2021). Climeworks. https://act.climeworks.com/fight-climate-change-video/?utm_source=google&utm_medium=cpc&utm_campaign=GS-AO-Top4-en-Generic&utm_term=carbon capture&gclid=CjwKCAjwgr6TBhAGEiwA3aVuITpmQTDXAnKMFeykjAzpR9ecyjtDZBkQ7I0DFyr85XfYJRaFzgsdnxoC7VkQAvD_BwE

Erans, M., Sanz-Pé rez, E. S., Hanak, D. P., Clulow, Z., Reiner, D. M., & Mutch, G. A. (2022). Direct air capture: process technology, techno-economic and socio-political challenges. This Journal Is Cite This: Energy Environ. Sci, 15, 1360. https://doi.org/10.1039/d1ee03523a

Gbrielli, P., Gazzani, M., & Mazzotti, M. (2020). The role of carbon capture and utilization. I&EC Research, 59, 7033–7045.

Royal society of chemistry. (2022). Direct air capture: process, technology and challenges. Energy Environ. Sci., 15, 1360–1405.

Socolow, R., Desmond, M., Aines, R., Blackstock, J., Bolland, O., Kaarsberg, T., Lewis, N., Mazzotti, M., Pfeffer, A., Sawyer, K., Siirola, J., Smit, B., & Wilcox, J. (2011). Direct Air Capture of CO2 with Chemicals.

US Environmental Protection Agency. (2012). Carbon Sequestration through Reforestation.

van Egmond, S., & Hekkert, M. P. (2012). Argument map for carbon capture and storage. 11.