The State of the Science for Marine Carbon Dioxide Removal (mCDR) – A Summary for Policy Makers

The State of the Science for Marine Carbon Dioxide Removal (mCDR) – A Summary for Policy Makers

Authors: Chris Vivian* (WG Co-Chair), Miranda Boettcher*, Philip Boyd (WG Co-Chair), Alejandro H. Buschmann, Long Cao, Olaf Corry, Mike Elliott, Aarti Gupta, Clare Heyward, Rahanna Juman, Alana Lancaster, Nadine Mengis, Christine Merk, Andreas Oschlies, Masahiro Sugiyama, Guanqiong Ye.

Affiliation: Members of GESAMP Working Group 41 (www.gesamp.org/work/groups/41)

*Corresponding authors: chris.vivian2@btinternet.com, miranda.boettcher@swp-berlin.org

In 2019 GESAMP Working Group 41 published a report titled ‘High Level Review of Wide Range of Proposed Marine Geoengineering Techniques’ (GESAMP, 2019[1]). It reviewed 27 approaches (including variations of approaches) including Carbon Dioxide Removal (CDR), Albedo Modification (AM), and hybrid (i.e., for purposes extending beyond CDR or AM) technologies. The report was one of the first high-level assessments of ‘marine geoengineering’ interventions. The report highlighted that the assessment was not able to be fully comprehensive, and that there was a need to further “Foster the development of socio-economic, geopolitical and other relevant societal aspects of marine geoengineering assessments, including societally relevant metrics where possible, to ensure a holistic approach to subsequent assessment process(es)”.

Since 2020, there has been a surge of interest in marine CDR (mCDR) techniques to store carbon in ocean reservoirs using a range of methods. However, all of these techniques are in the early stages of development with much still to learn about their potential efficacy, environmental impacts and societal implications. Most interest is currently focused on ocean alkalinity enhancement (which includes mineral, electrochemical and electrodialysis techniques), biomass sinking (e.g. crop wastes and macroalgae) into the deep ocean, direct ocean capture of CO₂ and ocean iron fertilization (OIF), which pose many technical, environmental, political, legal and regulatory challenges, among others. This increased interest is reflected in the continuing significant increase in the number of scientific papers on mCDR, the growing number of start-ups developing mCDR techniques, the significant funding for mCDR research announced by the US and the EU in 2023 and the current consideration of potential regulation of several mCDR techniques by the London Protocol Parties. This has led to significant number of field trials/pilot studies taking place or being planned in the marine environment for a range of mCDR techniques.

The paper will review the current state of the science for mCDR techniques with a focus on those techniques that are currently under active investigation.

[1]http://www.gesamp.org/site/assets/files/1996/rs98e-1.pdf