Climate change mitigation requires a massive reduction of greenhouse gas (GHG) emissions and even negative emissions in the near future. To achieve GHG mitigation, low-carbon technologies are developed. However, environmental benefits are not generally proven since most technologies require significant amounts of low-carbon energy and interact in complex energy systems. Moreover, low-carbon technologies comprise a wide range of maturity and varying data availability. Assessing the full range of low-carbon technologies requires life-cycle assessment (LCA), from screening to an integrated energy system design at the concept, process, plant to system level.

At the concept level, we demonstrate handling of limited data availability and apply an LCA-based short-cut method enabling a best-case ranking of CO2-based chemicals. Half of these products have the potential to provide environmental benefits already today through shortened synthetic pathways and low H2 demand. In contrast, the other products could only achieve environmental benefits when sufficient low-carbon electricity is available.

Using a process from the best-case ranking, we expand the LCA model scope to the process level providing a more detailed environmental assessment for the example of CO2-based oxymethylene ethers (OME) fuels. Our well-to-wheel analysis shows a significant potential to decrease local pollutants, whereas climate impacts are only reduced if large amounts of low-carbon energy are available.

Subsequently, we extend the LCA model scope to the plant level exemplary for direct air capture (DAC). We demonstrate that climate benefits strongly depend on the electricity supply and the subsequent application of CO2: permanent storage leads to negative emissions, whereas using CO2 as feedstock for fuels could reach carbon neutrality at best. Furthermore, large-scale deployment of DAC, e. g., capturing 1% of global annual CO2 emissions, will not be limited by energy and materials requirements and will increase other environmental impacts by much less than 1%.

Our analyses emphasize the environmental potential of low-carbon technologies and their dependence on low-carbon energy; however, neglecting their cross-sectoral interconnectivity in the energy system. Therefore, we extend the scope of LCA to the system level by developing an energy system model with integrated LCA. The computed low-carbon transition pathways lead to many co-benefits in other environmental impact categories but also cause burden-shifting, which needs to be considered when developing climate mitigation strategies.