Air Pollution and Its Association with the Greenland Ice Sheet Melt

Round 1

Reviewer 1 Report

It is an interesting topic, the manuscript is very well written and I believe it deserved publication.

My only comment:

Fig. 1 – The authors should specify in figure caption what exactly is presented at subfigures a), b), c) and d)

Author Response

We thank the reviewers for their insightful comments and suggestions, which indeed helped us improve the quality of our manuscript to a large extent. All our replies are reflected in the main text with yellow markings and explained below point by point.

Reviewer #1:

It is an interesting topic, the manuscript is very well written and I believe it deserved publication.

ANS] Thank you very much for the kind acknowledgement of our work. The manuscript has now been updated substantially as per the comments and suggestions received from the reviewer.

 1] Fig. 1 – The authors should specify in figure caption what exactly is presented at subfigures a), b), c) and d).

ANS] Thank you very much for the nice suggestion. Figure 1 caption has now been suitably updated to clarify the meanings of panels (a), (b), (c), and (d).

----------------------------------------------------------------------------------------------------------------

Reviewer 2 Report

I have read the manuscript “Air pollution and its association with the Greenland Ice Sheet melt” by Vikrant et al for consideration in Sustainability.  This review touches upon aerosols of various sources and their implications on Greenland Ice Sheet (GrIS) melt processes.  The review is quite timely and would be of interest to a wide audience both studying and generally interested in anthropogenic and global climate change drivers of GrIS melt. However, it is rather thin in places (i.e. Section 4), requiring expansion in the breadth of literature cited with specific focus directed on GrIS impacts and implications.  Below I offer a few comments/questions that should be expanded to these shortcomings. 

Line numbers should be added to the manuscript for ease of review, but as they are omitted, comments are referenced by page (P) and paragraph (p) number from the top of each page.

P1, p2 (Introduction): You briefly mention large-scale atmospheric circulation patterns here and in section 3, including the North Atlantic pathway (e.g. NAO and Greenland blocking) (Hanna et al., 2016, 2018) and deeper (lower-latitude) Atlantic transport by way of atmospheric rivers (Mattingly et al., 2018), to advect pollutants presumably out of industrial centers to the GrIS.  Along these lines, what impacts have changes in the frequency, intensity and duration of atmospheric patterns and meridional atmospheric circulation anomalies had on lower latitude pollutant transport to the GrIS?  The above referenced studies could be mentioned in this discussion.  Since Greenland blocking has a warming effect on West Greenland and Baffin Bay, as documented in many studies across the last decade, is regional aerosol deposition focused on the westernhalf of the GrIS?  An expansion of the atmospheric circulation discussion touching upon these spatiotemporal components is warranted and appropriate in such a review, perhaps as its own section. 

P3, p2: Since this is deemed a review (last sentence of the Abstract), why is a materials and methods section included?  Rather, datasets can just be mentioned in the context of the summarized findings.

P4, p1/4: Have studies, including ones cited, attempted to differentiate local aerosol (cooking, ship traffic, forest fires on the island) vs remote aerosol (industrial activity, combustion of fossil fuels, dust deposition by desert biomes) forcing of GrIS albedo change and melt?  If so, it would be a good idea to isolate these scales in such a discussion.

P4, p5: How do aerosols and BC shorten cloud lifespan?  This statement requires description of the processes involved and references to other studies that provide such evidence.

P5, p3: How does this decline in ice sheet albedo overlap emissions trends, boreal forest fire activity, and changes in large-scale circulation.  These components should all be expanded upon and related as appropriate to regional dark zone area (decreasing albedo) and surface mass balance changes on the GrIS.

P6, p2: Anthropogenic emissions are reduced to zero due to deforestation or afforestation?

P6, p3: Are there hotspots of wildfire activity that appear to consistently contribute to BC deposition on the GrIS?  How can research studies be designed going forward to measure the effects of year-to-year changes in extent and location of fire activity on GrIS melt?  More broadly, what are the major unanswered questions in pollution-GrIS melt research?  Also, this sentence does not make sense and requires clarification: “During the most recent two decades, ice sheet melting for the last decade has been slowing down with the steady loss of GIS.”

References

Hanna, E., T.E. Cropper, R.J. Hall, and J. Cappelen, 2016: Greenland blocking index 1851-2015: a regional climate change signal.  International Journal of Climatology, 36, 4847-4861, doi:10.1002/joc.4673.

Hanna E., R.J. Hall, T.E. Cropper, T.J. Ballinger, L. Wake, T. Mote, and J. Cappelen, 2018: Greenland Blocking Index daily series 1851-2015: Analysis of changes in extremes and links with North Atlantic and UK climate variability and change, International Journal of Climatology, 38, 3546-3564, doi:10.1002/joc.5516.

Mattingly, K.S., T.L. Mote, and X. Fettweis, 2018: Atmospheric river impacts on the Greenland Ice Sheet surface mass balance.  Journal of Geophysical Research Atmospheres, 123, 8538-8560, doi:10.1029/2018JD028714.

Author Response

We thank the reviewers for their insightful comments and suggestions, which indeed helped us improve the quality of our manuscript to a large extent. All our replies are reflected in the main text with yellow markings and explained below point by point.

Reviewer #2:

I have read the manuscript “Air pollution and its association with the Greenland Ice Sheet melt” by Vikrant et al for consideration in Sustainability. This review touches upon aerosols of various sources and their implications on Greenland Ice Sheet (GrIS) melt processes. The review is quite timely and would be of interest to a wide audience both studying and generally interested in anthropogenic and global climate change drivers of GrIS melt. However, it is rather thin in places (i.e. Section 4), requiring expansion in the breadth of literature cited with specific focus directed on GrIS impacts and implications. Below I offer a few comments/questions that should be expanded to these shortcomings.

ANS] Thank you very much for the kind acknowledgement of our work. The manuscript has now been updated substantially as per the comments and suggestions received from the reviewer.

 1] Line numbers should be added to the manuscript for ease of review, but as they are omitted, comments are referenced by page (P) and paragraph (p) number from the top of each page.

ANS] Thank you very much for the nice suggestion. The manuscript was prepared as per the template provided by the journal for the review process. Since the template does not incorporate line numbers, we did not add them. We appreciate the reviewer’s comments and suggestions for the improvement of our manuscript.  

2] P1, p2 (Introduction): You briefly mention large-scale atmospheric circulation patterns here and in section 3, including the North Atlantic pathway (e.g. NAO and Greenland blocking) (Hanna et al., 2016, 2018) and deeper (lower-latitude) Atlantic transport by way of atmospheric rivers (Mattingly et al., 2018), to advect pollutants presumably out of industrial centers to the GrIS. Along these lines, what impacts have changes in the frequency, intensity and duration of atmospheric patterns and meridional atmospheric circulation anomalies had on lower latitude pollutant transport to the GrIS? The above referenced studies could be mentioned in this discussion. Since Greenland blocking has a warming effect on West Greenland and Baffin Bay, as documented in many studies across the last decade, is regional aerosol deposition focused on the westernhalf of the GrIS? An expansion of the atmospheric circulation discussion touching upon these spatiotemporal components is warranted and appropriate in such a review, perhaps as its own section.

ANS] Thank you very much for the nice comment. A new section has now been added (Section 4, pages 4-5) to clarify the atmospheric circulation of air pollutants to the Greenland ice sheet.

3] P3, p2: Since this is deemed a review (last sentence of the Abstract), why is a materials and methods section included? Rather, datasets can just be mentioned in the context of the summarized findings.

ANS] Thank you very much for the nice suggestion. The title of Section 2 has now been updated appropriately for a better understanding.

 4] P4, p1/4: Have studies, including ones cited, attempted to differentiate local aerosol (cooking, ship traffic, forest fires on the island) vs remote aerosol (industrial activity, combustion of fossil fuels, dust deposition by desert biomes) forcing of GrIS albedo change and melt? If so, it would be a good idea to isolate these scales in such a discussion.

ANS] Thank you very much for the nice comment. New sentences (Section 5, pages 6-7) and Figure 4 have now been added to differentiate the impact between local and remote aerosols.

5] P4, p5: How do aerosols and BC shorten cloud lifespan? This statement requires description of the processes involved and references to other studies that provide such evidence.

ANS] Thank you very much for the nice comment. New sentences have now been added to section 4 (page 4) to clarify the effect of anthropogenic aerosols on the cloud lifespan.

 6] P5, p3: How does this decline in ice sheet albedo overlap emissions trends, boreal forest fire activity, and changes in large-scale circulation. These components should all be expanded upon and related as appropriate to regional dark zone area (decreasing albedo) and surface mass balance changes on the GrIS.

ANS] Thank you very much for the nice comment. New sentences (Section 5, pages 6-7) have now been added to further discuss ice sheet albedo, light-absorbing impurities, atmospheric circulation, dark zone albedo difference, and emission trends.

7] P6, p2: Anthropogenic emissions are reduced to zero due to deforestation or afforestation?

ANS] Thank you very much for the nice comment. ‘Deforestation’ has now been replaced by ‘afforestation/reforestation’ (section 5 (page 6)).

 8] P6, p3: Are there hotspots of wildfire activity that appear to consistently contribute to BC deposition on the GrIS? How can research studies be designed going forward to measure the effects of year-to-year changes in extent and location of fire activity on GrIS melt? More broadly, what are the major unanswered questions in pollution-GrIS melt research? Also, this sentence does not make sense and requires clarification: “During the most recent two decades, ice sheet melting for the last decade has been slowing down with the steady loss of GIS.”

ANS] Thank you very much for the nice comment. New sentences (Section 5, pages 6-7) have now been added to discuss the impact of wildfire activity on the Greenland ice sheet melt.

----------------------------------------------------------------------------------------------------------------

Reviewer 3 Report

General Comments:

This is a review paper on the association between air pollution and Greenland ice sheet melt. The authors have reviewed a decent amount of literature to discuss the geophysical relations between black carbon and aerosols that interact with clouds and ice. However, the authors have not specifically mentioned any future potential for research. The paper reads more like a broad literature review of a journal paper rather than a “review” paper. It is okay to use figures from other sources with permission, but the authors could have provided a figure of their own to illustrate the processes involved. A map showing the movement of vessels and burning of fossil fuel (globally) and their effect on Greenland ice sheet with arrows suggesting the locations of oscillations would have made more scientific sense. Moreover, the review paper should also highlight a gap to provide suggestions and guidance for future research – which is missing in this paper.

Unfortunately, with the current version of the paper, I cannot recommend publication. If the authors address the comments I made above, I am sure they can produce a better review paper than this one. I also have a few specific comments that may help the authors to look at finer details while writing a manuscript.

Specific Comments:

1. Abstract: Please mention the methods used in the study (e.g., how the review was done) and some highlights of the findings. Currently, the abstract is more focused on the background of the study. The abstract should also briefly mention what has been done (i.e., data and methods) and what are the primary outcomes/findings.
2. Page 2: Right before Eq 1. Instead of saying “…can be found elsewhere”, please just mention the source.
3. 1: The terms involved are not properly explained.
4. Figure 2 appears before it is referred to in the text. Please move it below the description.
5. Figure 3: Y-axis: Please mention the unit properly (i.e., full form of Gt)
6. Page 4, 2^nd paragraph: The formatting of the text doesn’t match with the rest of the paper.
7. Page 4: Please mention the full form of Gt
8. Please mention the full form of ng while referring to it for the first time.
9. Page 5: Please abbreviate GHG (i.e., greenhouse gas) before using the abbreviated form.
10. Page 6: The second paragraph has different formatting compared to the rest of the texts on the page.
11. Page 6: “…CO2 emissions are reduced to zero overnight due to other factors (e.g., deforestation) – shouldn’t it be reforestation?
12. Conclusions: This section is too generic. There is no real suggestions or guidance for future studies.

Author Response

We thank the reviewers for their insightful comments and suggestions, which indeed helped us improve the quality of our manuscript to a large extent. All our replies are reflected in the main text with yellow markings and explained below point by point.

Reviewer #3:

This is a review paper on the association between air pollution and Greenland ice sheet melt. The authors have reviewed a decent amount of literature to discuss the geophysical relations between black carbon and aerosols that interact with clouds and ice. However, the authors have not specifically mentioned any future potential for research. The paper reads more like a broad literature review of a journal paper rather than a “review” paper. It is okay to use figures from other sources with permission, but the authors could have provided a figure of their own to illustrate the processes involved. A map showing the movement of vessels and burning of fossil fuel (globally) and their effect on Greenland ice sheet with arrows suggesting the locations of oscillations would have made more scientific sense. Moreover, the review paper should also highlight a gap to provide suggestions and guidance for future research – which is missing in this paper. Unfortunately, with the current version of the paper, I cannot recommend publication. If the authors address the comments I made above, I am sure they can produce a better review paper than this one. I also have a few specific comments that may help the authors to look at finer details while writing a manuscript.

ANS] Thank you very much for the kind acknowledgement and critique of our work. The manuscript has now been updated substantially as per the comments and suggestions received from the reviewer.

 1] Abstract: Please mention the methods used in the study (e.g., how the review was done) and some highlights of the findings. Currently, the abstract is more focused on the background of the study. The abstract should also briefly mention what has been done (i.e., data and methods) and what are the primary outcomes/findings.

ANS] Thank you very much for the nice suggestion. The data collection and literature survey methodology has been clarified in Section 2 (page 3). Furthermore, the abstract was suitably updated.

 2] Page 2: Right before Eq 1. Instead of saying “…can be found elsewhere”, please just mention the source.

ANS] Thank you very much for the nice suggestion. The concerned sentence (section 1 (page 2)) has now been updated accordingly.

 3] Figure 1: The terms involved are not properly explained.

ANS] Thank you very much for the nice comment. Figure 1 caption has now been suitably updated to clarify the meanings of the utilized terms.

 4] Figure 2 appears before it is referred to in the text. Please move it below the description.

ANS] Thank you very much for the nice comment. Figure 2 has been positioned in sequence after Figure 1. The placement was made as per the space available in the template provided by the journal. As Figure numbering and in-text reference are in order, we did not make any changes. If the journal requests us for figure repositioning for typesetting concerns, we may do so accordingly.

 5] Figure 3: Y-axis: Please mention the unit properly (i.e., full form of Gt).

ANS] Thank you very much for the nice comment. Figure 3 has now been suitably updated.

6] Page 4, 2^nd paragraph: The formatting of the text doesn’t match with the rest of the paper.

ANS] Thank you very much for the nice comment. The concerned paragraph (section 3 (page 4)) has now been suitably reformatted.

 7] Page 4: Please mention the full form of Gt.

ANS] Thank you very much for the nice comment. The full form of ‘Gt’ (gigatonne) has now been provided in the manuscript.

8] Please mention the full form of ng while referring to it for the first time.

ANS] Thank you very much for the nice comment. ‘ng’ stands for ‘nanogram.’ As ‘ng’ is a standard and internationally recognized symbol for nanogram, a specific explanation about its full form is not warranted.

9] Page 5: Please abbreviate GHG (i.e., greenhouse gas) before using the abbreviated form.

ANS] Thank you very much for the nice comment. ‘GHG’ has now been replaced by ‘greenhouse gas’ (section 5 (page 5)).

10] Page 6: The second paragraph has different formatting compared to the rest of the texts on the page.

ANS] Thank you very much for the nice comment. The concerned paragraph (section 5 (page 6)) has now been suitably reformatted.

11] Page 6: “…CO2 emissions are reduced to zero overnight due to other factors (e.g., deforestation) – shouldn’t it be reforestation?

ANS] Thank you very much for the nice comment. ‘Deforestation’ has now been replaced by ‘afforestation/reforestation’ (section 5 (page 6)).

 12] Conclusions: This section is too generic. There is no real suggestions or guidance.

ANS] Thank you very much for the nice comment. The ‘conclusions’ section has now been suitably updated.    

----------------------------------------------------------------------------------------------------------------

Round 2

Reviewer 3 Report

The authors have addressed my comments. Thank you for your work.