Six years after I myself called for the usage of CCS (Carbon Capture and Storage), I have now come to the realization that this was a mistake. Why this change of heart?
Natural carbon sinks versus CCS
Natural CO2 sinks such as forests, soils, wetlands and even algae could absorb much more CO2 if they were promoted and protected accordingly. All organic materials, living organisms, plants and bacteria store carbon in their cells until they decompose into smaller carbon units. The smallest of these units are carbon dioxide or methane. In the case of trees, this decomposition can take several thousand years. In permafrost soils, the plant leftovers remain frozen until they thaw and start emitting again. These processes can also occur in wetlands if they are reused as farmland. Simple rewetting would almost completely halt the degradation processes here. These natural “technologies” deserve more attention.
Unfortunately, this is not happening. The German government just suggested a law allowing underground storage due to their struggle with hard-to-abate emissions. At the same time, the IPCC necessarily expects natural sinks to at least triple their CO2 uptake in the coming decades. Hardly anyone is talking about this. No one starts planting trees – not even in their own gardens. This is not part of European carbon emissions trading, and farmers cannot benefit financially from near-natural reforestation or leaving land to nature.
One hectare of forest for example could absorb around 10-25 tons of CO2 per year. Germany is 30% forested, which corresponds to around 11 million hectares. However, deforestation, forest dieback and wildfires cause that this potential won’t be reached even closely. In the case of wetlands, on the other hand, agricultural conversion – i.e. draining – causes up to 40 tons of CO2 emissions per hectare. This is happening due to the decay processes mentioned above. Natural peatlands often emit little methane and bind some CO2.
Forests and peatlands are being deliberately destroyed globally to use the areas for agriculture (often related to meat or soy production). This destruction contributes massively to CO2 emissions. Healthy forests could store hundreds of gigatons globally, if we would let them.
At the same time, we should not forget that 99.9% of the Earth’s carbon – several hundred million gigatons in total – is also bound in the lithosphere as sedimentary rocks. Limestone, dolomite and other rocks consist of carbonates with a high content of calcium and/or magnesium. Over millions of years, these carbonates have formed from marine organisms and through natural chemical precipitation. This precipitation can be caused by changes in salinity, pH or temperature as CO2 is highly water soluble (with reduced solubility with increasing temperature). This can also easily be done in any laboratory.
Technical solutions and their problems
Unfortunately, underground storage solutions such as CCS are being promoted instead. They are seen as the next big business opportunity. CO2 is being captured, purified and, if necessary, transported very far to the seashore in a yet-to-be-created transportation system and injected into geological structures with new deep bore holes. However, this involves numerous risks and is extremely costly.
The idea behind CCS is: CO2 is „stored“ savely in underground geological formations. While at some locations supercritical CO2 was mainly being suggested for enhanced oil recovery, because CO2 is a good solvent for organic compounds, usually the CO2 dissolves in any water present and forms carbonates if the circumstances are right.
However, these phase transitions will cause micro earthquakes and leakages to some degree. Underground geological layers often don’t have clear boundaries, which means that the CO2 can diffuse uncontrollably in different directions. This could even penetrate into groundwater layers and cause serious environmental problems.
An example from Germany is the pilot plant in Ketzin, where CO2 storage was operated and tested from April 2004 to December 2017. It shows that the underground distribution of CO2 is not exactly as predicted. From an injection site hundreds of meters deep, the CO2 is being distributed in a point-like manner in rock layers. In reality, it is distributed in various directions, which can lead to clumping on the one hand and wide distribution and unwanted leaks on the other.
In Australia, the Glencore Carbon Transport and Storage Corporation’s Surat Basin Carbon Capture and Storage (CCS) project was also recently halted by the authorities due to its potential impact on groundwater resources.
In Canada, Capital Power Generation canceled a $2.4 billion CCS project in early May. They stated that although the project was technically feasible, it was not economically viable.
Climeworks: a ray of hope?
One company in the field of technical CO2 sinks that should be highlighted is the Swiss company Climeworks. Their technology captures CO2 directly from the air using adsorption-desorption technology and pumps it, dissolved in water, into deep boreholes on site. This has the advantage that CO2 does not have to be transported over long distances and there are no intermediate steps in CO2 processing.
However, in addition to the geological risks of underground storage, which may also require constant re-drilling to depths of up to 1 km, this process is currently also very expensive: CCS at Climeworks costs around 1,300 $ per tonne of CO2. Despite the increase in efficiency, the fundamental question remains as to whether the large-scale technical storage of CO2 underground is the right approach.
Economic considerations
Instead of storing CO2 in the underground, it could be used above ground and reused in various industries. Magnesium carbonate costs around 50 euros per kilogram, calcium carbonate around 20 euros, and even 500 grams of CO2 cost around 10 euros in a household soda cartridge. These materials could also be used in cement production or for other industrial purposes instead of being considered „waste“ as promoted by CCS interest groups.
Circular economy instead of underground storage
In my opinion, we should strive for a circular economy in which materials are reused instead of “stored” underground in a risky and irretrievable way. The concept of the circular economy aims to use resources efficiently and minimize waste. CO2 could be dissolved in water, precipitated using brine, for example, and deposited in above-ground storage facilities. This would not only conserve resources, but also minimize the environmental impact. At the same time, it would reduce global dependencies, as a large proportion of carbonates first have to be extracted in mines, processed and imported into the EU and the US.
Conclusion
Technical CO2 sinks are to be scaled up to huge quantities over the next few decades in order to reduce global CO2 emissions. But instead of relying on unsafe and expensive solutions, we should promote and protect natural CO2 sinks. The answer lies in a sustainable and well thought-out circular economy that conserves natural resources and protects the environment at the same time.
CCS may be a tempting solution on paper – as it was for me, but the reality is that it is neither profitable nor reliable. Nature already provides us with the tools to capture CO2 effectively – we just need to use and promote them properly. Despite some positive aspects of technologies like from Climeworks, we should focus on natural solutions and a circular economy approach to be successful in the long term and reach the climate targets.
The German Bundestag will soon have to decide how Germany positions itself on this topic.