The umbrella term negative emission technologies (NET) describes different nature-based and technological methods to remove CO₂ from the atmosphere and store it long term (so-called carbon dioxide removal (CDR) methods). CDR methods include the targeted expansion of the storage capacity for carbon in plants and soils, the enrichment of recycled and carbon-storing building materials and their reuse, the capture of CO₂ by means of technical and chemical processes from the ambient air or from industrial processes, and the capture in long-term storage sites.
Thanks to innovative research projects and companies in the field of CDR methods, Switzerland is currently a leader in the development and application of some of these processes, such as the production of carbon-negative cement or the direct capture of carbon from the air. However, the further development, market introduction and scaling of these approaches face many challenges. On the one hand, it is difficult to acquire the necessary financial resources for research and development, to find implementation partners in industry and to obtain permits for test facilities. On the other hand, the further expansion of processes that are already marketable requires an expansion of the supply of renewable energies, the development of sustainable storage options and functioning logistics for biomass and carbon.
Last but not least, the public must be informed about the advantages, disadvantages and possible risks of the different processes, and a broad discourse about corresponding uncertainties and ambiguities must be initiated. In order to ensure a sustainable expansion of NET, this process should also include the political decision-makers who are responsible for ensuring a conducive political and legal framework in the future.
Currently, the expansion of the following CDR methods is being discussed:
Afforestation + Reforestation
Forest management measures that optimize and increase the CO₂ uptake of woodlands by expansion, protection or reforestation. A sustainable management ensures that the carbon is bound in the soil and living biomass of healthy forests for a long time. Further, this approach can include using wood for long-lived products or energy production in cascaded use.
Biochar + Soil Carbon Sequestration
Conversion of biomass (e.g. harvest residues) into mineral-rich charcoal at high temperatures and in the absence of oxygen (i.e. pyrolysis), making it resistant to decomposition. Allows to sink C in agricultural soils, with various co-benefits. This approach includes further agricultural practices that aim to increase the soil carbon content and thus uptake of CO₂ from the atmosphere. Biochar is also used outside agriculture. The production and storage of biochar is also called pyrogenic carbon capture and storage (PyCCS).
Direct Air Carbon Capture & Storage (DACCS or DAC+S)
Removal of CO₂ from ambient air through various chemical or engineering processes, e.g. adsorption, methanation or via hydroxide solutions (powered by residual heat or renewable energy). Captured CO₂ may then be stored long-term, e.g. by injecting it into depleted oil and gas fields or saline aquifers, or used in consumer goods and other applications.
Enhanced Weathering + Carbon Uptake in Cement
Application of minerals, such as rock powder, that naturally absorb CO₂ by chemical weathering, in terrestrial or aquatic systems. Depending on the used rock, nutrients are released and soil properties can be improved. This approach also includes enhanced CO₂ uptake in cement by means of concrete recycling technologies, e.g. the carbonation of crushed concrete materials, that allow long-term storage of captured CO₂ in built structures.
Bioenergy with Carbon Capture + Sequestration (BECCS)
Integration of carbon removal technologies in a wide range of industrial processes that convert biomass (i.e., put simply, carbon stored by/in plants) into products, such as fermentation, gasification or combustion. Carbon captured in e.g. combined heat and power plant, in biogas plants, the paper and pulp industry or during ethanol production may then be stored long-term.
Cultivation + Restoration of Wetlands
As a natural carbon sink, wetlands generate biomass that conserves carbon dioxide, e.g. through the formation of peat in raised bogs. Thus, cultivating and restoring wetlands, peatlands and coastal habitats have the potential to combine long-term carbon absorption and storage with nature conservation.
