Direct air capture (DAC) may be critical for achieving stringent climate targets, yet the environmental implications of its large-scale deployment have not been evaluated. We used the IMAGE model to change the background data in Life Cycle Assessment (LCA) databases in order to do a prospective LCA of four different DAC technologies. We investigated the environmental impacts of DAC, the effect of a changing background energy system, the importance of technological learning, and the regional implications.
Our analysis shows that a rapid decarbonization of the power and energy demand sectors - that is consistent with the 1.5 °C climate target - can increase the net sequestration efficiency of DACCS and facilitate its climate change mitigation potential. This highlights that DACCS deployment and electricity system decarbonization should act synergistically in climate change mitigation efforts. A failure to do this could lead to important environmental trade-offs when using DAC.
Concerning environmental implications of DAC, electricity consumption is a major contributor to the terrestrial ecotoxicity and metal depletion levels of DACCS, which are mainly driven by the solar and wind penetration levels in the background electricity system in our scenarios. Therefore, as the decarbonization of the electricity system progresses with expanding renewable energy generation and storage capacities, additional efforts are needed to facilitate sustainable mining, manufacturing, and expanding the circular economy of energy materials used in those technologies, which will reduce these impact levels. Carbon management policies should consider research and development efforts to improve process and material efficiencies of DACCS and low-carbon energy generation technologies. Our results show that technology learning reduces levels of ecotoxicity, metal depletion, and water depletion (solvent-based DACCS only), highlighting its important role in avoiding potential environmental problem-shifting of DACCS deployment under a climate change mitigation pathway.
Whereas large-scale DACCS deployment will affect the supply and demand dynamics of the overall energy system, this effect is negligible compared to the effects of decarbonizing the power sector. Thus, the deployment of DACCS is complementary to the expansion of other net-zero emission technologies as well as BECCS in stringent climate change mitigation scenarios.