Exploring site-specific carbon dioxide removal options with storage or sequestration in the marine environment - The 10 Mt CO2 yr-1 removal challenge for Germany

Marine carbon dioxide removal (mCDR) and geological carbon storage in the marine 53 environment (mCS) promise to contribute to the mitigation of global climate change in 54 combination with drastic emission reductions. However, the implementable potential of mCDR 55 and mCS depends, apart from technology readiness, also on site-specific conditions. 56 In this paper, we explore different options for mCDR and mCS, using the German context as a case study. We challenge each option to remove 10 Mt CO2 yr-1 57 , which accounts for 8-22% of 58 projected hard-to-abate and residual emissions of Germany in 2045. We focus on the 59 environmental, resource, and infrastructure requirements of individual mCDR and mCS options 60 at a specific site, within the German jurisdiction when possible. Furthermore, we discuss main 61 uncertainty factors and research needs, and, where possible, cost estimates, expected 62 environmental effects, and monitoring approaches. 63 In total, we describe ten mCDR and mCS options; four aim at enhancing the chemical carbon 64 uptake of the ocean through alkalinity enhancement, four aim at enhancing blue carbon 65 ecosystems’ sink capacity, and two employ geological off-shore storage. Our results indicate that 66 five out of ten options would potentially be implementable within German jurisdiction, and three 67 of them could potentially rise to the challenge. This exercise provides a basis for further studies 68 to assess the socio-economic, ethical, political, and legal aspects for such implementations.