The aim of this study is to provide a transparent framework to evaluate the potential (in terms of sequestered and displaced carbon), and economics (in terms of cost of carbon avoided and removed) of a non-exhaustive selection of NETs pathways. Ecosystem and socio-economic impacts associated with their deployment is also quantified.

The study sets out to help the carbon capture and storage (CCS) community in trying to gain a better understanding of the costs and value of NETs. It also helps the modelling community in being able to better model the role of NETs; and policy/decision makers in having more information on costs, value and scalability of NETs.

Key Messages

• 11 key performance indicators (KPIs) have been defined and assessed for a select number of NET pathways, including direct air capture (DAC), biochar and bioenergy with CCS (BECCS) for power, fuel, hydrogen, steel and cement production.
• The highest CO2 removals are achieved in NET pathways that maximize the capture of CO2, have low energy conversion efficiencies, or have access to low-carbon energy. This is especially important when quantifying the net removal potential of DAC: if the energy is supplied by fossil sources, the amount of negative emissions generated lowers significantly.
• Except for corn-based ethanol, all BECCS to bioenergy pathways achieve net negative emissions in the range of 0.08 - 0.35 tCO2/GJ. Whilst hydrogen production pathways exhibit high capture rates, the energy conversion efficiency for these processes is also high, so less biogenic emissions are being sequestered in the process compared to other biofuel pathways. The production of biochar via slow pyrolysis leads to a net removal of 0.47-0.89 tCO2 per tonne of dry mass of feedstock (2.6-3.3 tCO2 /tchar).
• For pathways involving the production of bioenergy, the amount of CO2 emissions that can be avoided depends on the carbon intensity and on the products/fuel's substitution factor. In low-carbon power grids, biomass provides a much greater value in decarbonizing the transport sector by substituting gasoline than in the power sector.
• Configurations that maximize the CO2 capture perform better in terms of certain ecosystem impacts. Due to the lower permanence of carbon in soil compared to geological storage, the production of biochar results in the largest water and land footprints among all routes investigated. These trade-offs might be lower when accounting for the potential long-term agricultural benefits of biochar in soil, which have not been included in the present analysis.
• Recommendations:
         - Demonstration of NETs at scale to improve and validate the existing data.
         - NETs should be included in new and existing emission trading schemes.