Global Significance of Mangrove Blue Carbon in Climate Change Mitigation

Round 1

Reviewer 1 Report

Please check out the pdf attached.

Comments for author File: Comments.pdf

Author Response

This manuscript by Alongi did a very nice inventory of mangrove forest carbon stocks across the globe. By compiling very recent data across the globe, the author drew a conclusion of insignificant role of mangrove systems in global climate mitigation but maybe of national or regional significance. I concur with the author on the significance of conducting such a study towards closing the gaps in global carbon budget uncertainties. First of all, let’s just put aside this conclusion in terms of its validity. Just based on this very conclusion, does the author agree the title could be more accurate with ”global insignificance” instead of ”global significance”? However, I am a little skeptical about the affirmative statement of global insignificance of mangrove forest in climate mitigation. The author concluded this based on the small proportion of mangrove forest carbon in global carbon stock (though with data uncertainties remained, which the author acknowledged). My opinion is that it is still too early to draw this conclusion. Instead, I believe we should hold a holistic view of the Earth System, especially when discussing climate mitigation by natural systems. I totally agreed that it is now relatively certain to say, regionally, mangrove forest is pivotal in regulating carbon budgets. However, in a intricately interrelated Earth System the collapse of mangrove forests in one region would be possible to cascade across the globe, affecting climate in other regions and globally. This entails further investigations. Therefore, I would recommend the author tones down the statement of global insignificance of mangrove forests in climate mitigations. I agree it is reasonable to state explicitly mangrove forests account for a small portion of global carbon stock in natural systems. There are still steps from carbon stocks to climate mitigation. Here are a couple of suggestions on the presentation, which is already clear and coherent though. First, is it better to present the numbers of carbon stocks in different systems visually in bar charts or other appropriate ways instead of in tables? I thought it might be better for readers to receive the information more directly. Second, I believe the author can totally start a new section titled ’assessment of global significance’ (or similar) for the very last two paragraphs to highlight the discussion on importance of mangrove carbon. I thank Professor Wang for his thoughtful comments. In response I have toned down the "global insignificance' in the Abstract and have expanded the discussion of global significance into a new section 5 where I discuss the significance of mangrove mitigation in the tropical coastal ocean and in a number of countries, citing the recent assessment of Taillaret [9]. I have chosen to keep the data in tabular form to highlight the differences between countries and regions.

Reviewer 2 Report

I attached the reviewing report.　please check it.

Comments for author File: Comments.docx

Author Response

The manuscript entitled "Global Significance of Mangrove Blue Carbon in Climate Change Mitigation." submitted to Sci. by Alongi D.M.., was reviewed. The present MS is quite significant study, because it comprehensively included many data regarding carbon sequestration in mangrove ecosystems from quite numerous previous reports although some of papers that I knew were omitted in this MS. Considering the strategies of the sustainable management and conservation of mangrove blue carbon, those data will be quite useful and important. So, I do not have any concern for the acceptance of this MS in this journal. I thank this reviewer for his/her comments. I welcome any other information that I have not included in my manuscript, including unpublished papers or reports

Reviewer 3 Report

The paper proposes an overview about data information of Blue Carbon around the world. The author brings to discussion the impact of blue carbon in specific ecosystems and how no protecting it can impact the emission of C on the air. 

 

Event not presenting significant contributions to the theme, because as mentioned by the author since 2009 many papers were published. However, the author made an in-deep new analysis, where can improve acknowledgment research. 

 

There are a few points needed to be check in order to improve the paper, as follows. 

• At Table 1, indicate the meaning of "NA". Variable "n" in the final of the same table.
• As suggested by the author, there is a lot of differences between data information from the dataset base used by other authors. How the author can affirm what is the correct database information, or these differences are acceptable?
• In "As forests age, forest biomass and thus C stocks increase." the author can explain the bio reasons why the stocks increase when the forest is aging.
• Fig. 2 sounds to be a histogram representation, right? If yes, it is interesting to represent the data series along the time. Still, this graph shows that an exponential distribution can represent this behavior where can help researchers do statistic estimates.  (It is not mandatory this statement, but can improve the data analyses).
• Table 2 shows a location where data information was collected, but there is a "Modeled". Is it a typing error? The horizontal lines in this element are correct too?
• Table 3 is well done. 
• In "Mangrove CO2 emissions account for roughly 0.2% of total global CO2 emissions and account for about 18% of CO2 emissions from the tropical coastal ocean.", as a comparative the author could present the other CO2 emissions source. (It is a suggestion)

   

 

 

 

Author Response

The paper proposes an overview about data information of Blue Carbon around the world. The author brings to discussion the impact of blue carbon in specific ecosystems and how no protecting it can impact the emission of C on the air. Event not presenting significant contributions to the theme, because as mentioned by the author since 2009 many papers were published. However, the author made an in-deep new analysis, where can improve acknowledgment research. There are a few points needed to be check in order to improve the paper, as follows. At Table 1, indicate the meaning of "NA". Variable "n" in the final of the same table. As suggested by the author, there is a lot of differences between data information from the dataset base used by other authors. How the author can affirm what is the correct database information, or these differences are acceptable? In "As forests age, forest biomass and thus C stocks increase." the author can explain the bio reasons why the stocks increase when the forest is aging. Fig. 2 sounds to be a histogram representation, right? If yes, it is interesting to represent the data series along the time. Still, this graph shows that an exponential distribution can represent this behavior where can help researchers do statistic estimates. (It is not mandatory this statement, but can improve the data analyses). Table 2 shows a location where data information was collected, but there is a "Modeled". Is it a typing error? The horizontal lines in this element are correct too? Table 3 is well done. In "Mangrove CO2 emissions account for roughly 0.2% of total global CO2 emissions and account for about 18% of CO2 emissions from the tropical coastal ocean.", as a comparative the author could present the other CO2 emissions source. (It is a suggestion) I thank this reviewer for his helpful comments. 1. Regarding Table 1, I have corrected 'NA' to 'ND' 2. I have added a sentence in the Table 1 heading that I only used data from references in which sufficient detail was provided on Methods and that there was a sufficient level of replication. 3.In the text where I stated "As forests age, forest biomass and thus C stocks increase", I have expanded this text to explain the soil C stocks increase due to further accumulation of sediment and of root matter as roots grow and die; also, as canopies grow bigger, the AG C stocks will increase. 4. I have not changed Fig 2 as the data is not directly time-dependent; the purpose of the histogram was to show the wide spread of the data, but that most data points were less than 100 gC m-2 a-1. 5. I have corrected 'modelled' in Table 2. Thank you for spotting the error. 6. I have added more information on the contribution of other tropical ecosystems to the CO2 emissions from the tropical coastal ocean.

Round 2

Reviewer 1 Report

Thanks to the author for taking into consideration of my comments!

Reviewer 3 Report

The comments were analyzed, answered, and answered. Thank you!