Sea Level Rise and Future Projections in the Baltic Sea

Round 1

Reviewer 1 Report

The paper aims to provide an overview of the present sea level rise and future silver rise in the Baltic Sea, particularly on the Etonian coast. I have several major concerns about this manuscript, and my recommendation is that it needs substantial and extensive revisions before it may be eventually published.

A major concern related to section 3 this section is the voltage to stimulate the relative sea level rise in the Baltic Sea over the past decades. I failed to see the point of this section. as the manuscript clearly states relative sea level rise can be directly measured by tide gauges. Therefore, what is the rationale for indirectly estimating relative sea level rise, namely subtracting the absolute sea level rise measured by satellites and estimating vertical land movement by rheological models? This approach would make sense for future projections since climate models only simulate total sea level rise, but it needs to make sense to estimate observed trends. This whole section will be unclear for any reader that will be kept wondering what the purpose of evaluating relative sea level rise is when it can be directly measured.

2) A second concern is related to section 5. This section presents estimations of future sea level rise in the Baltic Sea based on projections by the IPCC. this Section glosses over important problems. the tool to estimate regional sea level rise by the IPCC is meant to be applied to open oceans and not Inland seas such as the Baltic Sea. The reason is that the spatial resolution of the climate models is of the Order of 100 kilometres at best. In many models, the Baltic Sea connection to the North Sea will be completely closed or open by 100 kilometres. both are unrealistic. therefore, this tool cannot be directly used to estimate future sea level rise in the Baltic or Mediterranean Sea, let alone to discriminate regions as small as the Estonian coast. The inaccurate representation of the connection between the North Sea, the North Atlantic, on the Baltic Sea means that even in the models in which the Baltic Sea is represented, several key processes will not be realistically represented, including the transport of heat from the North Atlantic into the Baltic Sea. In most IPCC models, the sea level rise in the Baltic Sea is just the result of the expansion of the water column in a relatively shallow sea and does not consider the transport of water mass and heat from the North Atlantic. At the very least, all those caveats must be mentioned and discussed to avoid the message that Baltic sea level projections from global climate models are accurate.

Related to this second concern is the missing citations to studies that have attempted to estimate sea level rise in the Baltic Sea addressing these problems, at least partially. One is the paper by Grinstedt et al.: Sea level rise projections for Northern Europe.

under RCP8.5, doi:10.3354/cr01309). The manuscript cites the BACC report, which, in turn, includes a summary of this paper, but this paper contains much more details about the estimations of regional sea-level rise. For instance, it explicitly cites that many AR5 models do not resolve the Baltic Sea, and only ten models do, and as I wrote, non represent the Kattegat straits realistically.

3) A third concern concerns the English used in the manuscript. The text would need considerable copy editing, deleting repetitive phrases and paragraphs. I haven't included here at least of possible corrections because they would be too numerous

4) The language is often inaccurate and more adequate for an informal publication than a scientific manuscript. For instance, the IPCC has not ‘prepared’ sea level models’. The IPCC sea level projections are based on different instruments: one is climate models, which simulate the expansion of the water column and the changes in the ocean currents; the second tool is expert guesses about the melting of the polar ice sheets in the future since this contributions cannot be modelled with the AR5 model suite. Therefore, the levels of uncertainty in these two contributions are vastly different and cannot be considered the result of a ‘sea-level model’.

Another example of inaccurate language is the description of the RPC scenarios. These scenarios are not based described in terms of future greenhouse gas concentrations but in terms of future radiative forcing. For instance, the RPC8.5 system assumes an anthropogenic radiative forcing of an additional 8.5 w/m2 by 2100. The radiative forcing is, of course, related to the concentration of greenhouse gases, but a scientific manuscript should be more careful and accurate when describing these terms

The manuscript needs to be revised by a native speaker , and many repetitions of sentences and paragraphs that state the same thing  need t be eliminated

Author Response

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Reviewer 2 Report

Dear Authors,

Paper is rather systematic and the results are useful. So, I can suggest paper for publication after minor corrections.

There are several recommendations for considering:

11)    Is it possible to change terminology like „relative“ and „absolute“  sea rise because clarity, like below Table 1: „corrected sea level data with ground uplift rates“ or „corrected  biases from sea level data“;

22)     Please clarify connection between equations (1) and (2). You introduced SLR in equation (1) and go back to the RSLR in equation (2). Is GIA (Δr) in equation (1) the same as LU in equation (2). What about Δg in equation (2)?

33)     IPCC AR6 green house emission scenarios would be preferable than IPCC AR5 but I believe that currently applied IPCC AR5 green house emission scenarios are good approximation of the recently available ;

44)     Some comments are in enclosed pdf.

Comments for author File: Comments.pdf

Author Response

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Reviewer 3 Report

This paper discussed sea level rise in the Baltic Sea. Overall, the topic of this paper fit within the stated scope of JMSE and this paper is basically well-organized and potentially useful for coastal flooding control. However, there are numerous questions I think need to be addressed. Therefore, my recommendation is major revision. The main questions I encountered when reading the manuscript are as follows:

Major editorial concerns

1、The title is not accurate. The authors can use new title such as ‘Sea level rise and future projections in the Baltic Sea’

2、The Abstract is not well written and needs to be rewritten. The authors do not explain the motivation of their study. What’s the problem of previous studies on sea level rise in the Baltic Sea? Furthermore, the authors should emphasize their new findings. After reading your abstract, I know that the authors do many things, but I do not know what’s new.

3、The Introduction is also not well-written. As indicated by the authors and my knowledge, there are several studies have discussed sea level rise in the Baltic Sea using the combination of satellite altimeters, tide gauges and numerical models. Then, what motivates your study (the limitations of previous studies)? Are your study data, method, and findings all consistent with previous studies (the novelty of your study)? Finally, I wonder whether this paper is a research paper or review paper (since the authors use the word ‘overview’ many times)?

Major technical concerns:

Since there are numerous long-term tide gauges in the Baltic Sea, the authors should provide spatial patterns of sea level rise in this region based on tide gauges. Table 1 only provides some spatially-averaged values. By comparison with absolute sea level rise rate from multi-satellite altimeters (Figure 2), the rate of land uplift can be determined, which can be used to validate the NKG2016LU and EST2020VEL model. These are necessary since the authors want to provide a comprehensive overview of sea level rise in the Baltic Sea.

Minor concerns:

English can be further improved.

L17. delete ‘with’

L40. delete ‘the’

L59. change ‘a threat’ to ‘threats’

L106 delete ‘the’ before ‘sea level’

L116 change ‘Two main methods’ to ‘Two types of data’

L122 delete ‘the’ before tide gauges

Figure 1. More information can be provided. For example, you can use color to represent the length of records at analyzed tide gauges.

L163  change ‘to studying’ to ‘to study’

L190 rewrite this sentence

L208 change ‘of’ to ‘in’

L469-470 rewrite this sentence

English can be further improved.

Author Response

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Reviewer 4 Report

General comments:

1. It is necessary to indicate the accuracy of Tide gauges sea level measurements and how it has changed over time.  It is necessary to indicate the accuracy NKG2016LU.

2. What is final accuracy of map Relative sea level rise on figure 5? We need to understand the final accuracy of this resuls. Please add commetns to the text.

3. In the introduction, there are not enough references to I. Medvedev's work on fluctuations in the Baltic Sea, for example, https://www.researchgate.net/publication/336945178_Low-Frequency_Baltic_Sea_Level_Spectrum

it is also necessary to add to the review several works where future climate projections are used for the wind waves analysis in the Baltic

https://www.researchgate.net/publication/333523864_Wave_Climate_Change_in_the_North_Sea_and_Baltic_Sea

https://www.researchgate.net/publication/324127683_Long-term_statistics_of_storms_in_the_baltic_barents_and_white_seas_and_their_future_climate_projections

https://www.mdpi.com/2073-4441/13/2/167

4. Does gravity change when the land rises or falls? can this affect the altimetry data? are there trend maps based on the GRACE project data?

5. It is necessary to justify the choice of a model for forecasting the future level in 2100. We know that there are a lot of models within CMIP6, some of them give sea level. Why is ESA selected?

Minor commetns:

1. Line 168-169 "with an average accu-168 racy of 80 ± 70 mm". For what time averaging this estimates is relevant? one day or one year?

2. Please add the graphs of Sea Level rise based on Tide gauges and based on satellite altimetry.

3.  Line 244-245 please add several more links to level model implemented for the Baltic sea. It is not only Esa model.

4. In abstract please add shortly about future projection methods

5. Figure 13 - please add the geografical coordinates.

Author Response

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Round 2

Reviewer 1 Report

The manuscript has been, in my opinion, satisfactorily revised. I have just one particular comment regarding section 4.1 and Figure 5.

This section estimates the relative sea level rise in mm/year along the Baltic Sea coast, based on satellite altimetry and land-uplift models. The section and the figure caption do not mention to which period these estimates apply. Are they current rates of sea-level change, or are they average over the last couple of decades (which ones)? 

Also, the reader would be interested to know whether these estimates agree with the measured relative sea-level rise at particular tide gauges or whether there are big differences. I could not find that comparison in the manuscript, but perhaps I missed it.

Author Response

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Reviewer 3 Report

This paper can be accepted.

Author Response

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Reviewer 4 Report

Thank you for the good job.

But Several comments remained:

1. "It is necessary to indicate the accuracy of Tide gauges sea level measurements". Response to reviewer: A paragraph has been added that indicates the accuracy of tide gauges sea level measurements and how it has changed over time."

I can not find the accuracy of level gauges/ +-1 cm or 1 mm? Pleaase add the clear information and links

2. "It is necessary to justify the choice of a model for forecasting the future level in 2100.  Why is ESA selected? Response to reviewer: Yes, we know that there are other sea level models. But since the ESA model is one of the latest official models from them, we found it reliable to use. It also includes data from various satellite altimetry missions, and the time series is also long."

I am sorry, but it is not argumented answer "ESA model is one of the latest official models". Please find the Esa and other models qulity, models time-spatial resolutions and explain your choice with strong science arguments.

3. "Please add the graphs of Sea Level rise based on Tide gauges and based on satellite altimetry. Response to reviewer: Thanks for the suggestion, but we find that the tables 1 and 2 show what the sea level rise"

Sorry, but it is very hard to understand trends in table. Please Put the time-grafs for different points based on level gauses and altimetry. It is not hard, but it is needed.

Author Response

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Round 3

Reviewer 4 Report

thank you. it is ok.