the Creative Commons Attribution-NonCommercial 4.0 Deed License.
the Creative Commons Attribution-NonCommercial 4.0 Deed License.
A computationally efficient method to model Stratospheric Aerosol Injection experiments
Abstract. Climate model simulations incorporating stratospheric aerosol injection (SAI) generally require more computational resources compared to out-of-the-box applications, due to the importance of stratospheric chemistry. This presents a challenge for SAI research, especially because there are numerous ways and scenarios through which SAI can be implemented. Here, we propose a novel method that allows SAI simulations to be performed without interactive stratospheric chemistry, saving a significant portion of the computational budget. The method requires a pre-existing dataset of an SAI experiment and its corresponding control experiment, with active stratospheric chemistry. The data is converted into a set of relations to determine the forcing fields given any required optical depth of the aerosol field. This makes the method suitable for applications that use dynamical feedback controllers. The results of climate simulations with aerosols prescribed by our method are in close agreement with those from full-complexity model, even for different model versions, resolutions and forcing scenarios.
Status: final response (author comments only)
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RC1: 'Comment on egusphere-2025-1476', Anonymous Referee #1, 10 May 2025
This is a fantastic paper. The work that the authors have done has the power to make complex geoengineering simulations more accessible. The development and exploration of the methodology are done quite well. I do have some comments:
I don’t have a sense of pros and cons, i.e., when this simpler method would work versus when you need a more complex model like WACCM. I don’t expect anything thorough, but if the authors could provide some opinions on this, it would be helpful.
There are situations where the authors claim to have explored a variety of scenarios and conclude that the method is robust to different scenarios. This is only partially true. You may get different answers if you use a different background scenario, for example one with strong mitigation or changes in tropospheric aerosols, as that will change the spatial patterns of forcing. Some appropriate caveats would be useful.
Lines 152-153: I think providing more details about the simulations here would be useful. I got a little lost. I suggest moving Table C1 into the main body of the text and expanding it so that it has more information about the specifications of each simulation.
Bullets on page 3: This is essentially pattern scaling. There’s a lot of literature you can lean on to show that this is a sensible thing to do.
Line 101: What does “similar” mean?
Line 186: I think you mean monotonically?
Section 2.2: It would be useful if you said somewhere that the approximations you make are good enough for this purpose, as the point of a feedback algorithm is to correct for such uncertainties. MacMartin et al. and Kravitz et al. both say this if you need citations.
Line 241: Your errors seem kind of high. Looking at Figure 2, an error of 0.4°C is a lot. This likely means your controller isn’t tuned as well as it could be, which isn’t a big deal, but it would be worth saying so.
Figure 2: I found the panels confusing, in that you’re mixing and matching units.
Line 257: Per the above comment, maybe change “well” to “adequately”.
Line 292: This is correct but also a strawman argument. You didn’t try to restore the climate completely.
Figure 5: I’m having trouble making sense of how important these results are. I wonder if you could compute z-scores (or something like that) so I would know whether the CAM minus WACCM differences are large compared to the natural variability of WACCM.
I did not find the paragraph on lines 376, nor Appendix B, terribly convincing. If you heat the stratosphere by 24°C, you are going to have substantial influences on ozone, and we know that ozone has an influence on surface climate. I would be more comfortable if you simply said that this is what you did, its effects of ozone changes on climate are likely smaller than the effects of the stratospheric heating on climate, and this should be explored further. That puts you on much safer ground.
Lines 400-402: Kravitz et al. (2014) demonstrated that the controller is likely robust to these sorts of differences. That gives some confidence that your controller indeed can handle this.
Lines 427ff: See recent work from the Cornell group, specifically led by Farley or Brody. They’re doing the initial steps of what you propose.
Code availability: Journals tend to want a fixed repository (e.g., Zenodo) rather than a changeable repository (Github).
Citation: https://doi.org/10.5194/egusphere-2025-1476-RC1 -
AC1: 'Reply on RC1', Jasper de Jong, 17 Jun 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-1476/egusphere-2025-1476-AC1-supplement.pdf
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AC1: 'Reply on RC1', Jasper de Jong, 17 Jun 2025
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RC2: 'Comment on egusphere-2025-1476', Anonymous Referee #2, 26 May 2025
This manuscript by de Jong at al. is trying to do two things: first, it is trying to describe how to prescribe stratospheric aerosols forcing in a different model. Second, it’s trying to show the surface climate differences in two different CESM1 versions (CESM2-CAM6, CESM1 and CESM2-WACCM6) forced by the same aerosol fields (prescribed, in the case of CAM).
The main thing I take issue with, in the first part, is that essentially what they are proposing to do is not novel at all. Prescribing an aerosol field externally is something that has been done before multiple times not just for volcanism (the entirety of CMIP6 historical simulations used prescribed aerosols) but for SRM, too. Conveniently, the authors leave out all the references of this, trying to pass it off as “novel”. Personally, I deeply dislike this way of not acknowledging past work (or to avoid performing a literature search that would have made past works emerge) to hype up one’s own.
Here are three main examples:
- Tilmes et al. (2016) proposed a prescribed aerosol forcing file for models with no interactive sulfate cycle. Such forcing field was then used in Xia et al. (2017) and in one of the models for G6sulfur (CNRM) as described in Visioni et al. (2021).
- Still in G6sulfur, the model MIP prescribed their own aerosol field and scaled them up in their two fully-coupled versions, also as described in Visioni et al. (2021).
- Finally, Tilmes et al. (2024) proposed a new experiment for CCMI with a new aerosol field for SAI, also describing climatic differences in WACCM when fully interactive vs prescribed aerosols are used, with much more details provided on how to prescribe the aerosols fields in different models provided in Jörimann et al. (2025). Reading Jörimann et al. (2025) could also illuminate for the authors how hard it is to prescribe aerosol fields in other models’ version, as one needs to get optical properties that might be treated differently in different models with different ways to translate aerosol size distribution to forcing.
None of this is ever acknowledged in the (rather short and non comprehensive in general) cited literature, giving the reader the impression that this is the first time something like this has been attempted (cue the word “novel” used frequently in the text, and also in the Key Points).
So, what’s novel? The use of a scaled-up, mono-dimensional control algorithm (not that different from what was used in multiple G6 models, see above) used in multiple publications starting in MacMartin et al. (2014)? That’s hardly new – and the simplified controller used here hardly seem well tuned, considering the pretty large errors shown in Fig. 2!
The second part then offers a description of surface climate differences between CAM and WACCM. This part (which would also not be particularly fitting for GMD on its own) is awfully lacking as well.
First, I don’t see any kind of discussion of the biases between the two models’ versions without SAI, and I think that would be a fundamental starting point to understand the sources of differences to a forcing. Even very similar versions of CESM2-WACCM6 that differ by the inclusion or not of tropospheric chemistry can present relevant distinctions in some modeled trends (see i.e. Davis et al., 2023), let alone two basically different models. Aside from surface climate, most of the differences in the stratospheric response are also left very vague (for instance, Section 3.3 essentially doesn’t offer anything more than guesses (“These features occur in Control as well and are assumed to be model differences”) that don’t really provide much confidence to the reader that the authors know what they’re talking about. The entire paragraph from l. 376 to l. 384 is very high level, does not cite any of the relevant literature about the impacts of stratospheric ozone changes on surface climate (to begin with, but the list is very long, see Bednarz et al., 2022).
I do not wish to claim that novelty in itself makes a study worthy of being published, and actually I think quite the contrary: but a study that wishes to claim novelty as its main strength, fails to deliver and also ignores relevant literature that would help frame this work in the broader context (out of curiosity, the manuscript has 24 references, of which 7 are in the first paragraph to prove/disprove the permissibility of SRM research or to discuss climate change, one of them is a non-peer reviewed link to CarbonBrief, and one a never accepted preprint from 2023, casually including one of the authors of this piece) is setting itself up to fail for anyone who has any familiarity with the field.
This manuscript, in another venue but GMD, could provide some interesting analyses of what happens when you prescribe the same aerosol field in different model’s versions given much more in depth, careful analyses, exploring the sensitivities, performing further experiments (i.e. different scenarios, which are available in CESM2-WACCM6, could be compared with the same prescribed CAM6 results to understand if the differences observed are a function of magnitude, of the specifics of the AOD pattern, of the broader atmospheric response, of the underlying emission scenario; the ozone field could have actually been changed; CAM6 simulations with fixed SSTs could have been performed to understand the actual forcing response; different patterns of AOD from different injection locations could have been combined to understand the linearity of the response, etc. The authors do acknowledge that “It might be worthwhile to expand the method for additional use cases.” But, given the paucity of interesting results otherwise, I think they should be the ones, and not somebody else at a later date). In its current form, however, I cannot recommend publication in this venue.
References
Bednarz, E. M., Visioni, D., Banerjee, A., Braesicke, P., Kravitz, B., & MacMartin, D. G. (2022). The overlooked role of the stratosphere under a solar constant reduction. Geophysical Research Letters, 49, e2022GL098773. https://doi.org/10.1029/2022GL098773
Davis, N. A., Visioni, D., Garcia, R. R., Kinnison, D. E., Marsh, D. R., Mills, M., et al. (2023). Climate, variability, and climate sensitivity of “Middle Atmosphere” chemistry configurations of the Community Earth System Model Version 2, Whole Atmosphere Community Climate Model Version 6 (CESM2(WACCM6)). Journal of Advances in Modeling Earth Systems, 15, e2022MS003579. https://doi.org/10.1029/2022MS003579
Jörimann, A., Sukhodolov, T., Luo, B., Chiodo, G., Mann, G., and Peter, T.: A REtrieval Method for optical and physical Aerosol Properties in the stratosphere (REMAPv1), EGUsphere [preprint], https://doi.org/10.5194/egusphere-2025-145, 2025.
Tilmes, S., Mills, M. J., Niemeier, U., Schmidt, H., Robock, A., Kravitz, B., Lamarque, J.-F., Pitari, G., and English, J. M.: A new Geoengineering Model Intercomparison Project (GeoMIP) experiment designed for climate and chemistry models, Geosci. Model Dev., 8, 43–49, https://doi.org/10.5194/gmd-8-43-2015, 2015.
Tilmes, S., Bednarz, E. M., Jörimann, A., Visioni, D., Kinnison, D. E., Chiodo, G., and Plummer, D.: Stratospheric Aerosol Intervention Experiment for the Chemistry-Climate Model Intercomparison Project, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2024-3586, 2024.
Visioni, D., MacMartin, D. G., Kravitz, B., Boucher, O., Jones, A., Lurton, T., Martine, M., Mills, M. J., Nabat, P., Niemeier, U., Séférian, R., and Tilmes, S.: Identifying the sources of uncertainty in climate model simulations of solar radiation modification with the G6sulfur and G6solar Geoengineering Model Intercomparison Project (GeoMIP) simulations, Atmos. Chem. Phys., 21, 10039–10063, https://doi.org/10.5194/acp-21-10039-2021, 2021.
Xia, L., Nowack, P. J., Tilmes, S., and Robock, A.: Impacts of stratospheric sulfate geoengineering on tropospheric ozone, Atmos. Chem. Phys., 17, 11913–11928, https://doi.org/10.5194/acp-17-11913-2017, 2017.
Citation: https://doi.org/10.5194/egusphere-2025-1476-RC2 -
AC2: 'Reply on RC2', Jasper de Jong, 17 Jun 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-1476/egusphere-2025-1476-AC2-supplement.pdf
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CEC1: 'Comment on egusphere-2025-1476 - No compliance with the policy of the journal', Juan Antonio Añel, 13 Jun 2025
Dear authors,
Unfortunately, after checking your manuscript, it has come to our attention that it does not comply with our "Code and Data Policy".
https://www.geoscientific-model-development.net/policies/code_and_data_policy.htmlYou have not published all the code necessary to replicate your manuscript in a suitable repository, as requested by our policy. This includes the CESM (CAM) code for the version that you have used here, and all the scripts that you have stored in a GitHub site. I should note that GitHub is not a suitable repository for scientific publication. GitHub itself instructs authors to use other long-term archival and publishing alternatives. Therefore, the current situation with your manuscript is irregular. Please, publish your code in one of the appropriate repositories and reply to this comment with the relevant information (link and a permanent identifier for it (e.g. DOI)) as soon as possible, as we can not accept manuscripts in Discussions that do not comply with our policy. Also, please include the relevant primary input/output data.
Also, you must include a modified 'Code and Data Availability' section in a potentially reviewed manuscript, containing the DOI of the new repositories.
I must note that if you do not fix this problem, we will have to reject your manuscript for publication in our journal.
Juan A. Añel
Geosci. Model Dev. Executive Editor
Citation: https://doi.org/10.5194/egusphere-2025-1476-CEC1 -
AC3: 'Reply on CEC1', Jasper de Jong, 17 Jun 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-1476/egusphere-2025-1476-AC3-supplement.pdf
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CEC2: 'Reply on AC3', Juan Antonio Añel, 17 Jun 2025
Dear authors,
What you mention as a solution to comply with our code and data policy is right. However, you must reply to this comment with such information, not simply state that you will do it. Please, do it, as the Discussions stage for your manuscript ends today, and such information should be public.
Juan A. Añel
Geosci. Model Dev. Executive Editor
Citation: https://doi.org/10.5194/egusphere-2025-1476-CEC2 -
CC1: 'Reply on CEC2', Claudia Wieners, 17 Jun 2025
Dear dr. Añel,
maybe the previous author reply was not 100% clear, because it didn't state any time line. We are working on the issue right now, i.e. extracting the relevant data sets for uploading on github and unifying the codes. I'm not sure if we will finish it today, but I'm confident we can do it within this week. Given that the previous comment attending us to the issue was made last Friday, i.e. just 2 workdays ago, we hope that a small extension of a few days can be granted, while we work on this as fast as possible. Apologies for not having finished this earlier; we mistakenly believed that this step would only be required upon acceptance of the article, as is common in many journals.
Kind regards
Claudia Wieners
Citation: https://doi.org/10.5194/egusphere-2025-1476-CC1
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CC1: 'Reply on CEC2', Claudia Wieners, 17 Jun 2025
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CEC2: 'Reply on AC3', Juan Antonio Añel, 17 Jun 2025
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AC4: 'Reply on CEC1', Jasper de Jong, 22 Jun 2025
Dear chief editor,
We have added the relevant code and data to the repository and published it with a permanent identifier. A revised version of the preprint, differing only in the Code and Data availability section, has been sent to the handling editor and uploaded to ESS Open Archive, where it is awaiting moderation. We sincerely hope our article now complies to GMD standards.
Kind regards,
Jasper de Jong
Citation: https://doi.org/10.5194/egusphere-2025-1476-AC4 -
CEC3: 'Reply on AC4', Juan Antonio Añel, 22 Jun 2025
Dear authors,
Many thanks for addressing this issue. However, you must publish the information here, in reply to this comment, not to submit a new version of your manuscript in the current stage.
Therefore, publish here the requested information, so that all the readers and reviewers can access it, which is what is necessary for the review and Discussion processes.
Juan A. Añel
Geosci. Model Dev. Executive Editor
Citation: https://doi.org/10.5194/egusphere-2025-1476-CEC3 -
AC5: 'Reply on CEC3', Jasper de Jong, 22 Jun 2025
Dear chief editor,
That was not clear to me. I will provide the additional information here:
The repository containing the feedback controller code, analysis code and data, used CESM settings and generated forcing files is provided at https://doi.org/10.5281/zenodo.15715224. The CESM model code is available from (https://www.cesm.ucar.edu/models/releases, last visited June 2025). WACCM geoengineering simulations for CESM2 and CESM1 are available at https://doi.org/10.5065/3WEZ-DD73 and https://doi.org/10.5065/D6JH3JXX, respectively. WACCM control simulations are published under CMIP5 and CMIP6 for CESM1 and CESM2, respectively, through the Earth System Grid Federation (ESGF: https://esgf-node.llnl.gov, last visited: June 2025).
Kind regards,
Jasper de Jong
Citation: https://doi.org/10.5194/egusphere-2025-1476-AC5 -
CEC4: 'Reply on AC5', Juan Antonio Añel, 22 Jun 2025
Dear authors,
Unfortunately, the site that you provide for the CESM/WACCM code does not comply with the requirements of our policy. Therefore, you must store the CESM/WACCM code you have used (the exact version) in one of the repositories acceptable according to our policy.
A similar issue happens with the links to the datasets that you provide. One of them is hosted by the NCAR RDA, and it is ok. However, the others are stored in the Climate Data Gateway, which is going to be deprecated by next August: in this case you should provide a new DOI for the RDA, instead of the link to the Climate Data Gateway. Regarding the simulations stored in the Earth System Grid Federation, two outstanding issues remain: First, we can not accept such site as a valid repository for scientific publication. Therefore, you must provide a different repository, one that complies with our policy, containing the data that you have used and is stored in the Earth System Grid Federation. I understand that full simulation outputs are too big in size for it, but we only request the exact variables that you use for your study, not full output files. Second, the current link that you provide, is simply a link to the main web portal, which makes hard for readers to identify what exact dataset you have used, where to find it and download it. This is why you need to provide a precise link and permanent identifier for the data you have used.
Please, address the above mentioned issues.
Juan A. Añel
Geosci. Model Dev. Executive Editor
Citation: https://doi.org/10.5194/egusphere-2025-1476-CEC4 -
AC6: 'Reply on CEC4', Jasper de Jong, 03 Jul 2025
Dear editor,
The issues you mentioned have been addressed. Here follows an overview of the code and data we published:
- Zenodo repository, https://doi.org/10.5281/zenodo.15715224, containing the feedback controller code, analysis code and data, used CESM settings and generated forcing files.
- Yoda* repository, https://doi.org/10.24416/UU01-84QO0O, containing the feedback controller code, used CESM settings and generated forcing files, pre- and postprocessing scripts, the CESM1(WACCM) control and geoengineering data, CESM model code, restart files and relevant model output.
- NCAR-RDA, https://doi.org/10.5065/3WEZ-DD73, containing the CESM2(WACCM) geoengineering data
- ESGF, https://doi.org/10.22033/ESGF/CMIP6.10115, containing the CESM2(WACCM) control data
* The data will be stored locally at Utrecht's University's YoDA system (https://www.uu.nl/en/research/yoda) where data will be stored for at least 10 years and is made publicly available via a DOI, complying with FAIR principles. Yoda is an infrastructure developed at the Utrecht University and provides an integrated collaboration, secure and (long-term) storage environment. The data will be preserved in a vault where the data are kept safe and cannot be tampered with.
We hope this is now sufficient to comply to your code and data policy.
Kind regards,
Jasper de Jong
Citation: https://doi.org/10.5194/egusphere-2025-1476-AC6
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AC6: 'Reply on CEC4', Jasper de Jong, 03 Jul 2025
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CEC4: 'Reply on AC5', Juan Antonio Añel, 22 Jun 2025
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AC5: 'Reply on CEC3', Jasper de Jong, 22 Jun 2025
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CEC3: 'Reply on AC4', Juan Antonio Añel, 22 Jun 2025
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AC3: 'Reply on CEC1', Jasper de Jong, 17 Jun 2025
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