Dear Tongwen,

Firstly, please accept my apologies for the delay in responding to your submission of a revised manuscript along with your responses to the two constructive reviews that you received.
Secondly, I’ve been asked by the Executive Editors that your manuscript be fully compliant with the requirements of Geoscientific Model Development. Specifically, I’m asking you to comply with the following:

1. The model source code is “freely available upon request”. This does not meet the requirements of the journal. If the source code is freely available, can you please archive it in accordance with GMD policy and update the code/data availability section of your manuscript? If it cannot be published, then you will need to indicate the licence conditions in the manuscript.
2. Model outputs on ESGF is very good practice but can be difficult to find. ESGF provides the correct data citation for each piece of data on the corresponding catalogue page, so can I please ask that you precisely cite the data? Precise instructions for citing CMIP6 data are here: https://docs.google.com/document/d/1SnwBL9MJQNEU1_nJ661SN3-SSxR0j1mAYan6-WXfaSU/edit
3. The model input files required to reproduce the simulations are not referred to. Again, may I please ask that you publicly archive these and update the code/data availability section accordingly?

You can find full details of the requirements of the journal for model description papers at:
https://www.geoscientific-model-development.net/about/manuscript_types.html#item1

Thirdly, on reading the reviewer comments, your responses to them, and the revised manuscript, I feel that you have addressed the majority of comments from Reviewer #1 with one exception as follows.

Reviewer #1 raised an important point about the imbalance in the TOA radiative fluxes in BCC-ESM. Although you cite Wild et al. (2013) to support that such an imbalance is common among other models, the comparison of models and the observational dataset used in that paper is referring to the present day, in which case an imbalance would be expected. However, in a pre-industrial control experiment as described in your manuscript, there is little anthropogenic forcing and as such, the TOA is expected to be more in balance. You clearly show little drift in surface temperature and sea surface temperatures in your Figure 1 but can you confirm whether BCC-ESM is indeed conserving energy?

In relation to Reviewer #2, they had concerns about the level of detail in the description of the aerosol scheme and how it compared with other existing schemes, and noted that the evaluation of the scheme itself in BCC-ESM1 was mainly qualitative and when quantitative, referred to quite old references.

I think the additional comparisons that you’ve made (e.g. HIPPO, Taylor plot) and the inclusion of more quantitative measures of skill (e.g. Table 7) add to the quality of the evaluation and the manuscript.

However, I would ask that you include information on the requested optical properties used (e.g. extinction co-efficient, asymmetry parameter etc..).

Finally, I also have a number of specific comments below that I ask you to implement.

Specific Comments:
1. When referring to GHGs, replace NO2 with N2O? (Line 86 of revised manuscript) and give full names e.g. nitrous oxide (N2O)
2. Please give complete names. As an example, replace CH2O with “formaldehyde (CH2O)” (Lines 142-144) and do likewise for all species referred to in the manuscript.
3. Replace “Wet removals …. are …” with “Wet removal … is …” (Line 138)
4. Please include appropriate references for CMIP6 biomass burning emissions, GHGs and solar forcing (e.g. van Marle et al., 2017)
5. The protocol for the CMIP6 coupled historical experiment is from Eyring et al. (2016). AerChemMIP (Collins et al., 2017) is using those historical ensemble members as controls for parallel sensitivity experiments. Please remove Collins et al. (2017) as the reference for the coupled historical simulation protocol (Line 307-308)
6. For N2O and CH4, it is still unclear whether they are only prescribed at the surface (and at the top boundary) and their concentrations in the remaining atmosphere are interactive. When you say “CH4, N2O, CO2, CFC11, and CFC12 are prescribed using CMIP6 historical forcing data as suggestion in AerChemMIP protocol. Although CH4 and N2O are prognostic variables in the chemistry scheme (Table 1), their prognostic values at each model step in the historical experiment are replaced by CMIP6 data“, are their concentrations replaced throughout the model domain or only at the surface and top boundary? Please clarify. Again here, Collins et al. (2017) and AerChemMIP are not the appropriate reference for the coupled historical protocol (Lines 310-313 and 378-380)
7. Give full name for ACCMIP (Line 333)
8. Change “eruption” to “eruptions” in Section heading (Line 354)

If you can address my query about the TOA radiative imbalance, implement the recommended changes in the specific comments, and comply with the requirements of GMD, I will be happy to recommend that your manuscript be accepted for publication.

Regards,
Fiona O’Connor

Dear Tongwen,

Thank you for your revised manuscript. Having read your response and your revised manuscript, and after consulting with the executive editors of GMD, I am writing to confirm that I can only recommend publication in GMD once you have adhered to GMD's strict policy on model code availability.

See below for an extract of what is written in relation to model code availability for model description papers at:
https://www.geoscientific-model-development.net/about/manuscript_types.html

The complete policy can be found at:
https://www.geoscientific-model-development.net/about/code_and_data_policy.html

The original manuscript stated that the model code was freely available. However, your latest response states that it is not ready for release. GMD do not accept this as a valid reason for not making the model code available - the model has been scientifically frozen, is being used to contribute to CMIP6, and underpins this paper. May I please ask that you make the model code (as used in the simulations described in your paper and from which you've archived data to the CMIP6 archive) available through a repository with a doi, and update your manuscript accordingly? I also ask that you make the input files used in the simulations available too, with relevant changes to the section on model code/data availability? You will see from the policy that GMD would like papers to include a user manual but it is not a strict requirement so, my request does not include making your user guide available.

This new model is a valuable contribution to CMIP6 and this paper is a valuable contribution to the scientific literature and to the climate research community. And you've had some very constructive reviews on your manuscript and you have addressed the other outstanding comments. However, it is only when the model code and model input files are made available that I will be able to accept your manuscript for publication in GMD. So, I would like to stress the importance of meeting the above requirements.

I do hope that you will be able to comply in a timely manner.

Regards,
Fiona O'Connor



Part of GMD's policy:
Code must be published on a persistent public archive with a unique identifier for the exact model version described in the paper or uploaded to the supplement, unless this is impossible for reasons beyond the control of authors. All papers must include a section, at the end of the paper, entitled "Code availability". Here, either instructions for obtaining the code, or the reasons why the code is not available should be clearly stated. It is preferred for the code to be uploaded as a supplement or to be made available at a data repository with an associated DOI (digital object identifier) for the exact model version described in the paper. Alternatively, for established models, there may be an existing means of accessing the code through a particular system. In this case, there must exist a means of permanently accessing the precise model version described in the paper. In some cases, authors may prefer to put models on their own website, or to act as a point of contact for obtaining the code. Given the impermanence of websites and email addresses, this is not encouraged, and authors should consider improving the availability with a more permanent arrangement. Making code available through personal websites or via email contact to the authors is not sufficient. After the paper is accepted the model archive should be updated to include a link to the GMD paper.

Dear Tongwen and co-authors,

Thank you for making the BCC climate model source code and input files available through a repository, including the provision of a doi.

However, I note that my request to precisely cite the model output data from the CMIP6 archive hasn't been addressed. May I please ask that you correct this, so that the revised manuscript fully complies with the GMD data policy?

As mentioned previously, model output on ESGF is very good practice but can be difficult to find. ESGF provides the correct data citation for each piece of data on the corresponding catalogue page. Precise instructions for citing CMIP6 data are here: https://docs.google.com/document/d/1SnwBL9MJQNEU1_nJ661SN3-SSxR0j1mAYan6-WXfaSU/edit

As soon as I'm satisfied that the model output is being cited precisely, I will accept your manuscript for final publication in Geoscientific Model Development.

Regards,
Fiona O'Connor

Dear Tongwen,

Many thanks for the various updates to make your manuscript fully compliant with the policies of Geoscientific Model Development.

I am pleased to inform you that I'm happy with your updates and recommend that your manuscript describing and evaluating the Beijing Climate Center Earth System Model be accepted for final publication in Geoscientific Model Development.

Regards,
Fiona O'Connor