The paper is a comprehensive and reasonable review article focused on coral reefs under local as well as global environmental changes, which would be valuable for researchers and managers in this field.

However, ｗhile the paper describes the concept as a threshold characterized by non-linear hysteresis or cascading effects resulting from positive and negative feedback loops, it falls short in offering a systemic elucidation of why the outcome becomes synergistic rather than merely additional from the point of system science. To rectify this critical shortcoming, urgent measures should be taken to enhance the originality and academic contribution of this paper. Strongly recommended actions include incorporating more quantitative analyses or empirical evidence supporting the discussed concepts and delving deeper into the systemic dynamics driving the observed phenomena.

In conclusion, the lack of an effective explanation due to the absence of original data significantly undermines the academic value of this paper. Consequently, the paper, in its current state, is more suitable for publication in a general introduction book rather than an academic journal.

Other specific comments:

Earth System Dynamic 0 2023-35

The paper reviews climate impacts on coral reefs to consider adjusting the tipping points for coral reefs. It is not clear until the conclusions that they are suggesting a further reduction in temperature thresholds from the original 1.5 estimates. There are many problems with this assessment that are briefly outlined below. Perhaps, the greatest is that it is a poor review of the literature in that it is out of date and selective citation of the literature. I only give a small number of papers that should be considered in a thorough and up-to-date review. The authors needs to do a systematic review of the recent literature and write a current status review that is more balanced, quantitative, and explains the decisions better.

There is also the problem of the tipping point definition and how it is measured and if they are rates or states, what is the time scale of the change, what are the specific irreversible changes, and what are the confidence intervals around estimates. There are two recent reviews that summarizes these problems well and would cause a reconsideration of the confidence in this new lower threshold.

Klein, S. G., C. Roch, and C. M. Duarte. 2024. Systematic review of the uncertainty of coral reef futures under climate change. Nature Communications 15:2224.

McClanahan , T. R. 2022. Coral responses to climate change exposure. Environmental Research Letters 17:073001.

Table 1 is the core finding of the paper but it still reads as poorly articulated draft. I would suggest the authors review the current literature, summarize it and present table 1 as a key element. Then, most of the text can focus on the evidence or lack of evidence for the conclusions in this table.  The authors could conclude with what are the key unknowns required to better estimate the tipping points. Otherwise, the current draft is an uncritical, out of date, and selective citation review of a much richer, data intensive, and nuanced coral reef literature that should be used to make these important conclusions.

Abstract

The abstract is diffciult to distinguish from similar conclusions of past work. It is not that clear or adding much to past work from my reading as the context of the works is missing.

What a tipping point threshold is should be defined early, otherwise the text is mysterious. I assume this is an irreversible change but that often depends on the time scale of observation and what is being measured. Readers will want to know.  

Usually, a sentences on methods for assessing tipping points is required to understand the results. It should be stated that this is a review.

The suggested tipping points seems similar to previous work, is it different and by how much?  What would cause it to change.

What are the uncertainties.  How were they addressed?

Introduction

It is important to distinguish states from rates.  Rates determine states but this is not clear and confused as written. The states are also vague, is is coral cover, calcification, ecological state and integrety, biodiversity, etc?

There is a much larger literature than is being cited here and the introduction seems to out of date given the many recent meta-analyses and reviews. I would suggest the authors look closer at the literature in the past 5 years and mostly cite these large data compilation studies. Much is being learned and it is not always in line with the general consensus that is being expressed in this paper. These are just a few examples that come to mind.

Davis, K. L., A. P. Colefax, J. P. Tucker, B. P. Kelaher, and I. R. Santos. 2021. Global coral reef ecosystems exhibit declining calcification and increasing primary productivity. Communications Earth & Environment 2:105.

Klein, S. G., C. Roch, and C. M. Duarte. 2024. Systematic review of the uncertainty of coral reef futures under climate change. Nature Communications 15:2224.

McClanahan , T. R. 2022. Coral responses to climate change exposure. Environmental Research Letters 17:073001.

Tebbett, S. B., S. R. Connolly, and D. R. Bellwood. 2023. Benthic composition changes on coral reefs at global scales. Nature Ecology & Evolution 7:71-81.

Shlesinger, T., and R. van Woesik. 2023. Oceanic differences in coral-bleaching responses to marine heatwaves. Science of The Total Environment 871:162113.

Walker, A. S., C. A. Kratochwill, and R. van Woesik. 2024. Past disturbances and local conditions influence the recovery rates of coral reefs. Global Change Biology 30:e17112.

It is worth remembering that permanent reversal and large scale changes is not just due to climate but also overfishing on large scales. These have been shown to have tipping points and large scale changes. Here is a recent meta-analysis paper.

McClanahan, T. R., A. M. Friedlander, L. Wantiez, N. A. J. Graham, J. H. Bruggemann, P. Chabanet, and R. M. Oddenyo. 2022. Best‐practice fisheries management associated with reduced stocks and changes in life histories. Fish and Fisheries 23:422 - 444.

P103 – this threshold is not being well suported by recent studies. There are many large studies that do not find this to be very useful.  Here is just one.

DeCarlo, T. M. 2020. Treating coral bleaching as weather: A framework to validate and optimize prediction skill. PeerJ 8:e9449.

If you are going to cite papers that use these threshold models, perhaps other approaches and findings should be cited as well. Low oxygen has been shown to be associated with higher coral cover, so the theory here is not supported empiricallly.

Vercammen, A., J. McGowan, A. T. Knight, S. Pardede, E. Muttaqin, J. Harris, G. Ahmadia, Estradivari., T. Dallison, E. Selig, and M. Beger. 2019. Evaluating the impact of accounting for coral cover in large‐scale marine conservation prioritizations. Diversity and Distributions 25:1564-1574.

McClanahan, T. R., and M. K. Azali. 2021. Environmental variability and threshold model’s predictions for coral reefs. Frontiers in Marine Science 8:1774.

There is a view that sea level rise will increase calcification but this was largely developed before the views of coral mortality. There are also the sediments and seabird studies that show increased nutrients improve reef condition and resilience.

Graham, N. A., S. K. Wilson, P. Carr, A. S. Hoey, S. Jennings, and M. A. MacNeil. 2018. Seabirds enhance coral reef productivity and functioning in the absence of invasive rats. Nature 559:250.

MacNeil, M. A., C. Mellin, S. Matthews, N. H. Wolff, T. R. McClanahan, M. Devlin, C. Drovandi, K. Mengersen, and N. A. J. Graham. 2019. Water quality mediates resilience on the Great Barrier Reef. Nature Ecology & Evolution 3:620.

L353 – the authors should give the reasoning for lowering the thresholds not just cite papers. The recent review by Klein et al 2024 indicate that lack of confidence intervals around thresholds.

Much of table 1 is out of date. However, they do cite Veron et al. 2029 to compensate for this problem. I look forward to reading it in 5 years. Authors should know the literature and how to organize and write a review and subsequently submit a more polished paper.