Dear authors,

the reviewers recommend your manuscript for publication after a number of major issues have been resolved and addressing a range of other suggestions.

As the editor I find that your proposed revisions largely address the reviewer’s concerns (somewhat more for reviewer #1 than for reviewer #2) and improve the manuscript in important respects. Thank you for responding to the comments made in a substantial manner.

I therefore ask you to submit a revised manuscript for publication that contains the changes you outlined in your responses.

As the editor, I would like to make some additional suggestions that you might want to consider when preparing the final revision of your paper.

Despite improved wording that describes the nature of your study and guards against an “overly optimistic” interpretation of results, I believe you still treat a full 3-fold increase of the world’s agricultural area in too casual a manner.

Agriculture is by far the main driver of environmental degradation, habitat loss and biodiversity decline today. Ecosphere stability is a critical issue because of these developments. Both at the poor end and at the industrial end unsustainable practices are wide-spread.

The huge expansion of agricultural area you model under what you claim are criteria of sustainability is largely not driven by the dynamic climatic feedback effects your model is built to take into account but by an enormous expansion of agriculture into land you deem available and suitable already under current climate (an expansion seen as being met essentially within the next decade, which already illustrates the highly artificial nature of the study).

Technically, geophysically, there is a basis for that, as you argue, but this is from a mostly hydroclimatic view of the Earth’s ecosphere, not an actual consideration of “sustainability” or even functional ecosphere stability. I think the limitations inherent to the approach suggest you should be explicit about the particular nature of the study you conducted through your advance in modelling – I do not think it is the actual carrying capacity of Earth. Nonetheless, you readily translate this huge expansion of land under direct human use into a carrying capacity that is also several times larger than the current world population. Can you do that with any confidence?

It is great progress that ESMs are beginning to enter this arena, however, the model approaches used are not superior to those used in the respective more disciplinary fields (that neglect the feedbacks) and therefore need to be treated with appropriate caution.

The strength of your approach, your core advantage, is a study of the feedbacks with the climate system. However, in agriculture these frequently are not the largest factor determining yields. What is more, in your manuscript you do not focus mostly on characterizing the effects of feedbacks, but equally on the overall total productivity, with implications e.g. for carrying capacity, which then requires confidence in the baseline results.

I am not criticizing that you venture into these fields, this is great progress for ESMs, but I am as sceptical as perhaps the reviewers of the real-world veractity of the results obtained. Despite your discussion of CFE and performance of runs without it, you heavily rely on it – as a consequence you see the largest carrying capacity under business-as-usual climate warming. This does not match established findings of the detrimental consequences of high-end climate change and should lead to a more careful, critical discussions of your own results – in your responses to the reviewers you tend to dismiss this aspect by stating that your results cannot really be compared to other studies and that you indeed see a decline in the no-CFE case.

Nonetheless, the paper merits publication as it reflects an important advance in Earth system modelling with comprehensive climate models, the study is done with competence and the manuscript is much improved in response to the reviewers. I particularly agree with the proposed change in title and look forward to your revised submission.

Thank you for paying such detailed attention to all the suggestions!
I hope you agree that the paper has benefited from the process - which now is complete!