Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Article
  • Published:

Mapping the global variation in the efficiency of ocean alkalinity enhancement for carbon dioxide removal

Nature Climate Change volume 15, pages 59–65 (2025)Cite this article

Subjects

Abstract

To limit global warming to below 2 °C by 2100, CO2 removal from the atmosphere will be necessary. One promising method for achieving CO2 removal at scale is ocean alkalinity enhancement (OAE), but there are challenges with incomplete air–sea CO2 equilibration, which reduces the efficiency of carbon removal. Here, we present global maps of OAE efficiency, and assess the seasonal variation in efficiency. We find that the equilibration kinetics have two characteristic timescales: rapid surface equilibration followed by a slower second phase, which represents the re-emergence of excess alkalinity that was initially subducted. These kinetics vary considerably with latitude and the season of alkalinity release, which are critical factors for determining the placement of potential OAE deployments. Additionally, we quantify the spatial and temporal scales of the induced CO2 uptake, which helps identify the requirements for modelling OAE in regional ocean models.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on SpringerLink
  • Instant access to the full article PDF.

USD 39.95

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: Global maps of OAE efficiency.
Fig. 2: Simulated OAE in four representative locations.
Fig. 3: Schematic diagram of a three-box model of CO2 equilibration dynamics and surface alkalinity dilution, following alkalinity addition.
Fig. 4: Fitted parameters plotted against latitude for January and July pulse releases.
Fig. 5: Decomposition of air–sea CO2 equilibration timescales.
Fig. 6: Assessment of the spatial extents of CO2 uptake.

Similar content being viewed by others

Data availability

The data of the CESM2 simulation output (the primary dataset in this study) are archived in analysis-ready cloud-optimized format (https://ieeexplore.ieee.org/abstract/document/9354557) in an open access AWS bucket kindly provided by Source Cooperative, and can be found at https://beta.source.coop/repositories/cworthy/oae-efficiency-atlas/. The CESM2 netCDF output files and a sidecar file of icechunk references are provided, which allow the entire dataset to be accessed via the Zarr protocol. This data availability facilitates the interpretation and extension of the research in this article, via parallel analysis of the entire dataset (∼200 TB of data when uncompressed) by accessing it as a single Xarray dataset (https://openresearchsoftware.metajnl.com/articles/10.5334/jors.148). Instructions for doing so can be found in the README.md file included with the data.

Code availability

The code for simulating OAE in CESM2 and data analysis are available on Zenodo (https://doi.org/10.5281/zenodo.13900162)31.

References

  1. IPCC Climate Change 2023: Synthesis Report (eds Core Writing Team, Lee, H. & Romero, J.) (IPCC, 2023).

  2. IPCC: Summary for Policymakers. In Climate Change 2021: The Physical Science Basis (eds Masson-Delmotte, V. et al.) (Cambridge Univ. Press, 2023).

  3. Wang, H. et al. Simulated impact of ocean alkalinity enhancement on atmospheric CO2 removal in the Bering Sea. Earth’s Future 11, e2022EF002816 (2023).

    Article  CAS  Google Scholar 

  4. Oschlies, A. et al. Guide to Best Practices in Ocean Alkalinity Enhancement Research (Copernicus Publications, 2023).

  5. Berner, R. A., Lasaga, A. C. & Garrels, R. M. The carbonate–silicate geochemical cycle and its effect on atmospheric carbon dioxide over the past 100 million years. Am. J. Sci. 283, 641–683 (1983).

    Article  CAS  Google Scholar 

  6. Kheshgi, H. S. Sequestering atmospheric carbon dioxide by increasing ocean alkalinity. Energy 20, 915–922 (1995).

    Article  CAS  Google Scholar 

  7. Zeebe, E. R. & Wolf-Gladrow, D. CO2 in Seawater: Equilibrium, Kinetics, Isotopes (Elsevier, 2001).

  8. Renforth, P. & Henderson, G. Assessing ocean alkalinity for carbon sequestration. Rev. Geophys. 55, 636–674 (2017).

    Article  Google Scholar 

  9. Jones, D. C., Ito, T., Takano, Y. & Hsu, W. Spatial and seasonal variability of the air–sea equilibration timescale of carbon dioxide. Global Biogeochem. Cycles 28, 1163–1178 (2014).

    Article  CAS  Google Scholar 

  10. He, J. & Tyka, M. D. Limits and CO2 equilibration of near-coast alkalinity enhancement. Biogeosciences 20, 27–43 (2023).

    Article  CAS  Google Scholar 

  11. Burt, D. J., Fröb, F. & Ilyina, T. The sensitivity of the marine carbonate system to regional ocean alkalinity enhancement. Front. Clim. 3, 624075 (2021).

    Article  Google Scholar 

  12. Humphreys, M. P., Daniels, C. J., Wolf-Gladrow, D. A., Tyrrell, T. & Achterberg, E. P. On the influence of marine biogeochemical processes over CO2 exchange between the atmosphere and ocean. Mar. Chem. 199, 1–11 (2018).

    Article  CAS  Google Scholar 

  13. Köhler, P., Abrams, J. F., Völker, C., Hauck, J. & Wolf-Gladrow, D. A. Geoengineering impact of open ocean dissolution of olivine on atmospheric CO2, surface ocean pH and marine biology. Environ. Res. Lett. 8, 014009 (2013).

    Article  Google Scholar 

  14. González, M. F. & Ilyina, T. Impacts of artificial ocean alkalinization on the carbon cycle and climate in Earth system simulations. Geophys. Res. Lett. 43, 6493–6502 (2016).

    Article  Google Scholar 

  15. Feng, E. Y., Koeve, W., Keller, D. P. & Oschlies, A. Model‐based assessment of the CO2 sequestration potential of coastal ocean alkalinization. Earth’s Future 5, 1252–1266 (2017).

    Article  CAS  Google Scholar 

  16. Ilyina, T., Wolf-Gladrow, D., Munhoven, G. & Heinze, C. Assessing the potential of calcium-based artificial ocean alkalinization to mitigate rising atmospheric CO2 and ocean acidification. Geophys. Res. Lett. 40, 5909–5914 (2013).

    Article  CAS  Google Scholar 

  17. Keller, D. P., Feng, E. Y. & Oschlies, A. Potential climate engineering effectiveness and side effects during a high carbon dioxide-emission scenario. Nat. Commun. 5, 3304 (2014).

    Article  Google Scholar 

  18. Kwiatkowski, L., Berger, M., Bopp, L., Doléac, S. & Ho, D. T. Contrasting carbon dioxide removal potential and nutrient feedbacks of simulated ocean alkalinity enhancement and macroalgae afforestation. Environ. Res. Lett. 18, 124036 (2023).

    Article  CAS  Google Scholar 

  19. Tamsitt, V. et al. Spiraling pathways of global deep waters to the surface of the Southern Ocean. Nat. Commun. 8, 172 (2017).

    Article  Google Scholar 

  20. Ho, D. T. et al. Measurements of air–sea gas exchange at high wind speeds in the Southern Ocean: implications for global parameterizations. Geophys. Res. Lett. 33, L16611 (2006).

    Google Scholar 

  21. Wanninkhof, R. Relationship between wind speed and gas exchange over the ocean revisited. Limnol. Oceanogr. Methods 12, 351–362 (2014).

    Article  Google Scholar 

  22. Yankovsky, E. et al. Impulse response functions as a framework for quantifying ocean-based carbon dioxide removal. Preprint at EGUsphere https://doi.org/10.5194/egusphere-2024-2697 (2024).

  23. Long, M. C. et al. Simulations with the Marine Biogeochemistry Library (MARBL). J. Adv. Model. Earth Syst. 13, e2021MS002647 (2021).

    Article  Google Scholar 

  24. Bach, L. T. The additionality problem of ocean alkalinity enhancement. Biogeosciences 21, 261–277 (2024).

    Article  CAS  Google Scholar 

  25. Danabasoglu, G. et al. The Community Earth System Model Version 2 (CESM2). J. Adv. Model. Earth Syst. 12, e2019MS001916 (2020).

    Article  Google Scholar 

  26. Yeager, S. G. et al. The seasonal-to-multiyear large ensemble (SMYLE) prediction system using the Community Earth System Model version 2. Geoscientific Model. Development 15, 6451–6493 (2022).

    CAS  Google Scholar 

  27. Kobayashi, S. et al. The JRA-55 reanalysis: general specifications and basic characteristics. J. Meteorol. Soc. Japan II 93, 5–48 (2015).

    Article  Google Scholar 

  28. Oschlies, A. Impact of atmospheric and terrestrial CO2 feedbacks on fertilization-induced marine carbon uptake. Biogeosciences 6, 1603–1613 (2009).

    Article  CAS  Google Scholar 

  29. Tyka, M. D. Efficiency metrics for ocean alkalinity enhancement under responsive and prescribed atmosphere conditions. Preprint at EGUsphere https://doi.org/10.5194/egusphere-2024-2150 (2024).

  30. Friedlingstein, P. et al. Global carbon budget 2023. Earth Syst. Sci. Data 15, 5301–5369 (2023).

    Article  Google Scholar 

  31. Long, M. et al. CWorthy-ocean/OAE-Efficiency-Map-v0: InitialRelease (InitialRelease). Zenodo https://doi.org/10.5281/zenodo.13900162 (2024).

Download references

Acknowledgements

This material is based on work supported by the National Center for Atmospheric Research, a major facility sponsored by the National Science Foundation under cooperative agreement no. 1755088. Any opinions, findings, conclusions or recommendations expressed in this material do not necessarily reflect the views of the National Science Foundation (NSF). We acknowledge high-performance computing support from Cheyenne (https://doi.org/10.5065/D6RX99HX) provided by the National Center for Atmospheric Research (NCAR) Computational and Information Systems Laboratory, sponsored by the NSF. This research used resources of the National Energy Research Scientific Computing Center, which is supported by the Office of Science of the US Department of Energy under contract no. DE-AC02-05CH11231. [C]Worthy acknowledges support from the Grantham Foundation for the Environment, Founders Pledge, the Chan Zuckerberg Initiative, ClimateWorks Foundation and Stripe. M.Z. acknowledges support from NSF grant no. OCE-1924270 awarded to J. Granger and S. Siedlecki at the University of Connecticut.

Author information

Author notes

  1. These authors contributed equally: Mengyang Zhou, Michael D. Tyka.

Authors and Affiliations

  1. Department of Marine Sciences, University of Connecticut, Groton, CT, USA

    Mengyang Zhou

  2. Google Inc., Seattle, WA, USA

    Michael D. Tyka

  3. Department of Oceanography, University of Hawaiʻi at Mānoa, Honolulu, HI, USA

    David T. Ho

  4. [C]Worthy, LLC, Boulder, CO, USA

    David T. Ho, Elizabeth Yankovsky, Scott Bachman, Thomas Nicholas, Alicia R. Karspeck & Matthew C. Long

  5. National Center for Atmospheric Research, Boulder, CO, USA

    Scott Bachman & Matthew C. Long

Authors
  1. Mengyang Zhou
    View author publications

    Search author on:PubMed Google Scholar

  2. Michael D. Tyka
    View author publications

    Search author on:PubMed Google Scholar

  3. David T. Ho
    View author publications

    Search author on:PubMed Google Scholar

  4. Elizabeth Yankovsky
    View author publications

    Search author on:PubMed Google Scholar

  5. Scott Bachman
    View author publications

    Search author on:PubMed Google Scholar

  6. Thomas Nicholas
    View author publications

    Search author on:PubMed Google Scholar

  7. Alicia R. Karspeck
    View author publications

    Search author on:PubMed Google Scholar

  8. Matthew C. Long
    View author publications

    Search author on:PubMed Google Scholar

Contributions

M.C.L., M.Z. and M.D.T. conceptualized the numerical experiments. M.C.L. and M.Z. performed the CESM2 model simulations to generate the underlying data. M.D.T. designed the box model. M.Z. and M.D.T. produced the figures. T.N. made the dataset publicly accessible. All authors contributed to the writing of the text. M.Z. and M.D.T. contributed equally to this work.

Corresponding authors

Correspondence to Mengyang Zhou or Michael D. Tyka.

Ethics declarations

Competing interests

The authors declare no competing interests.

Peer review

Peer review information

Nature Climate Change thanks the anonymous reviewers for their contribution to the peer review of this work.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary Figs. 1–11 and Discussion.

Supplementary Video 1

Evolution of surface pCO2 deficit, OAE efficiency and vertical distribution of excess ALK, for the simulated OAE experiments near Greenland.

Supplementary Video 2

Evolution of surface pCO2 deficit, OAE efficiency and vertical distribution of excess ALK, for the simulated OAE experiments in the Subpolar North Atlantic.

Supplementary Video 3

Evolution of surface pCO2 deficit, OAE efficiency and vertical distribution of excess ALK, for the simulated OAE experiments in the Subtropical North Atlantic.

Supplementary Video 4

Evolution of surface pCO2 deficit, OAE efficiency and vertical distribution of excess ALK, for the simulated OAE experiments in the Equatorial North Atlantic.

Rights and permissions

Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Zhou, M., Tyka, M.D., Ho, D.T. et al. Mapping the global variation in the efficiency of ocean alkalinity enhancement for carbon dioxide removal. Nat. Clim. Chang. 15, 59–65 (2025). https://doi.org/10.1038/s41558-024-02179-9

Download citation

  • Received:

  • Accepted:

  • Published:

  • Version of record:

  • Issue date:

  • DOI: https://doi.org/10.1038/s41558-024-02179-9

This article is cited by

Search

Advanced search

Quick links

Nature Briefing Microbiology

Sign up for the Nature Briefing: Microbiology newsletter — what matters in microbiology research, free to your inbox weekly.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing: Microbiology