Review Reports - The Impact of Urbanization on Carbon Emissions and Spatial–Temporal Differentiation Based on Meta-Analysis in China

Round 1

Reviewer 1 Report

Comments to the authors:

This manuscript demonstrated a study on the impact of urbanization on carbon emissions and spatial-temporal differentiation of China based on meta-analysis.

The authors had provided a clear clue to retests the relationship between urbanization and carbon emissions. However the principle of sample selection needs to be explained specifically in this manuscript. In addition, the characteristics of this study and discussion need to highlight and improve in this manuscript.

Therefore, I would like to recommend this manuscript make a major revision and give some suggestions and questions as following, which wish could help the authors improve the quality of their manuscript.

-Section Introduction.

The characteristics of this work need to be highlighted. The knowledge gap is not enough clear.

-Section Material and Methods:

a. Could you compare meta-regression with other general methods?

b. Why do you chooses such indicators of carbon emission?

-Table 1. Does the considerable difference of sample size between the sample literature influence the next analysis?

-Section Result :

a. the impact of urbanization in carbon emission is important in this work. So it needs to be explored deeply.

b. the reason of spatial differentiation of each areas need to be explained more specifically.

-Section Discussion. the authors could appropriately discuss the result of the tests. It is suggested to add the verification of the results by using empirical analysis or comparative analysis of literature.

-Section Conclusion:

a. the conclusion should add the specific results to support your findings.

Author Response

Dear editors and reviewers,

Thank you for comments on our manuscript entitled “ research on the impact of urbanization on carbon emissions and spatial-temporal differentiation based on meta-analysis”. These comments are very helpful for us to revise and improve our paper. Revised portions are highlighted by using track change mode. The responses to the main comments and each comment follow.

-Section Introduction.

1.The characteristics of this work need to be highlighted. The knowledge gap is not enough clear.

Answer：We introduced the research background more clearly in lines 28 to 51, and emphasized the importance of meta-analysis in such researches in lines 91-95, which helps to make the knowledge gap more significant.

-Section Material and Methods:

Could you compare meta-regression with other general methods?

Answer：We discuss the different between meta-regression and other general methods in lines 137-142.

3.Why do you chooses such indicators of carbon emission?

Answer：We gave the reason in lines 193-198. As a meta-analysis, the coefficients collected from the regressions in the sample empirical papers are usually used to indicate the magnitude of the effect.

4.Table 1. Does the considerable difference of sample size between the sample literature influence the next analysis?

Answer：Theoretically, the difference of sample size between the sample literature will not influence the meta-analysis because the overall effect size is computed as a weighted average of study-specific effect sizes, with more precise (larger) studies having larger weights. In “Table7. Results of Subgroup Analysis” we use a Q-test for heterogeneity caused by sample size in different groups, the results showed no significant.

-Section Result :

5.the impact of urbanization in carbon emission is important in this work. So it needs to be explored deeply.

Answer：We add Table 4 Main Effect of Urbanization on Carbon Emission in Different Subgroups in line 344-345 to explore the impact of urbanization in carbon emission in different indicators for calculating urbanization , CO2 and carbon emission. And the main effect was discussed more in the following text

6.the reason of spatial differentiation of each areas need to be explained more specifically.

Answer：In lines 385-395 we re-discussed the spatial differentiation of each area.

7.Section Discussion. the authors could appropriately discuss the result of the tests. It is suggested to add the verification of the results by using empirical analysis or comparative analysis of literature.

Answer：We added a new chapter “4.3 the verification of the results” to discuss and compare the results by a leave-one-out forestplot graph.

-Section Conclusion:

the conclusion should add the specific results to support your findings.

Answer：We added our specific results in lines 555-566.

Last but not the least, we want to thank you for your careful review of the paper, which very helpful for the improvement of the paper.

The authors

Reviewer 2 Report

The article “Research on the impact of urbanization on carbon emissions and spatial-temporal differentiation based on Meta-analysis“ is understandable and clearly written but need some revisions. The topic sounds not really novelty to me but is important. So, below are the points that the authors need to consider:

1. In the Introduction, clearly point out and explain the goal of the study.

2. There is a typo on the line 126. Should be Elsevier not Elsvier.

3. In chapter 2.1 you state that the meta-regression method is derived from the meta-analysis in the medical field. Can you add any example?

4. In the paper, you use the term positive relationship/effect/impact several times (specifically on lines 57 426 427 429 432). You even write in the Conclusion that "The positive impact of urbanization on carbon emissions has nothing to do with the selection of urbanization and carbon emissions indicators." So the question is, what does it have to do with it? This should be clear to the reader.

5. In Conclusion, clearly point out the scientific and professional contribution of this study and what are the recommendations or improvements in the continuation of the application of this methodology. Make it clear - what are the weaknesses and what are the advantages of the described methodological approach.

6. The authors should also discuss the future directions of their study in the Conclusion.

7. Because meta regression analysis uses the existing literature as the research sample is the 25 references really enough? Consider expanding your research sample.

I recommend that the authors should revise their manuscript to address the above concerns and resubmit their manuscript.

Author Response

Dear editors and reviewers,

-Section Introduction.

1.In the Introduction, clearly point out and explain the goal of the study.

Answer：We explained the purpose of the article in lines 108-116.

There is a typo on the line 126. Should be Elsevier not Elsvier.

Answer：Thank you for your advice, the typo has been corrected in the revised edition.

In chapter 2.1 you state that the meta-regression method is derived from the meta-analysis in the medical field. Can you add any example?

Answer：we have added some cases of meta-analysis in the evidence-based medicine field in lines 132-134.

In the paper, you use the term positive relationship/effect/impact several times (specifically on lines 57 426 427 429 432). You even write in the Conclusion that "The positive impact of urbanization on carbon emissions has nothing to do with the selection of urbanization and carbon emissions indicators." So the question is, what does it have to do with it? This should be clear to the reader.

Answer: Thank you for your valuable feedback. We reinterpreted the relationship between urbanization and carbon emissions in lines 555-566.

In Conclusion, clearly point out the scientific and professional contribution of this study and what are the recommendations or improvements in the continuation of the application of this methodology. Make it clear - what are the weaknesses and what are the advantages of the described methodological approach.

Answer: We discussed the limit and advantages of this paper in lines 567-584.

The authors should also discuss the future directions of their study in the Conclusion.

Answer: We discussed the future directions of this paper in lines 567-584.

Because meta regression analysis uses the existing literature as the research sample is the 25 references really enough? Consider expanding your research sample.

Answer: Thank you for your valuable advice. Now we have re-collected the literature and increased the number of samples to 49. Then we re-do the experiment in the article, so most of the experimental results are updated.

Last but not the least, we want to thank you for your careful review of the paper, which very helpful for the improvement of the paper.

The authors

Author Response File: Author Response.pdf

Reviewer 3 Report

1) References:

- Using a list of lumped references is not helpful to the readers. At least a short justification should be provided - individually.

- Unify in-text reference notation ([8] vs. Qiu et al. (2017))

- Make sure that all articles used in the text and tables are listed in the reference list (see Table 1).

2) Tab. 1: The selection seems to be focused mainly on China. Is it due to the availability of an article for this issue?

3) Are the results applicable in general or are they focused on a specific location according to the articles used?

4) Is it appropriate to use units of articles from different regions in meta-regression? Won't these articles cause unnecessary noise in the results?

5) Tab. 2: "1 if basic research controls the industrial structure, 0 otherwise". This is such an important factor for the production of emissions that it is not possible to consider it only as a binary variable. Industry has a significantly higher influence than urbanization itself. How is this effect treated in the results?

6) 3.2.1 Temporal differentiation effects: The influence of urbanization on the production of emissions is discussed here. But doesn't the type of industry, the wealth of the population (lifestyle), etc. play a significantly greater role? Isn't there a big correlation between urbanization and population wealth? And isn't the explanatory variable more connected to lifestyle than to urbanism itself? Doesn't urbanization at the time of house construction itself have a significant effect on the production of emissions? And once it's built, these emissions don't happen again. How is this effect treated?

7) What is the quality of the regression model? How much does it describe the variability in the data? Is the degree of uncertainty (interval estimates) not too great? What is the indicative value (I don't mean statistical significance) of the results?

8) Incorrect description: "Figure1. Funnel Plot of Main Effect"

9) It is obvious that urbanization leads to the efficiency of processes (transportation, healthcare, education, GDP, etc.). Efficiency in the case of emissions production can also be assumed, which results from the efficiency of processes in society. E.g. the advantage arising from the scale in heating houses, etc.

10) What does the article conclude other than that urbanization is positive for emissions production? What did the results bring about something new? Where will the results of this article be useful? Do the results of this article have any real impact?

Author Response

Dear editors and reviewers,

1.Using a list of lumped references is not helpful to the readers. At least a short justification should be provided - individually.

Answer: We put Table 1 in the article to show the basic characteristics of the selected samples. Now we have changed a new table to avoid misleading in line 213 in the revised edition.

2.Unify in-text reference notation ([8] vs. Qiu et al. (2017))

Answer: We have unified the in-text reference notation according to the format of periodical references of Sustainability in the revised edition.

3.Make sure that all articles used in the text and tables are listed in the reference list (see Table 1).

Answer: we have unified the in-text reference notation.

4.Tab. 1: The selection seems to be focused mainly on China. Is it due to the availability of an article for this issue?

Answer: We considered your question carefully. In fact, we mainly focus on the impact of China's urbanization on carbon emissions, so we changed the topic to “the impact of urbanization on carbon emissions and spatial-temporal differentiation based on meta-analysis in China”

5.Are the results applicable in general or are they focused on a specific location according to the articles used?

Answer: This paper mainly focuses on China's urbanization and carbon emissions, because China is currently the country with the largest carbon emissions in the world and China has experienced a very rapid urbanization process since these years. We explained the reason and background in section Introduction and in lines 170-172.

6.Is it appropriate to use units of articles from different regions in meta-regression? Won't these articles cause unnecessary noise in the results?

Answer: All the studies we collected are focus on China’s urbanization, and the study areas are very close. In order to avoid to make the results too sensitive, we used subgroup meta-analysis in table 4, table 5 , table 7 and the leave-one-out forestplot of the main effect to test the results.

7.Tab. 2: "1 if basic research controls the industrial structure, 0 otherwise". This is such an important factor for the production of emissions that it is not possible to consider it only as a binary variable. Industry has a significantly higher influence than urbanization itself. How is this effect treated in the results?

Answer: Thank you for your valuable advice. We redesigned the experiment and recollected the coefficient of proportion of secondary industry in sample literatures as an indicator of the industrial structure. Then in table 6 we showed the results which the industrial structure affecting the effect of urbanization on carbon emission treated as a control variable.

Temporal differentiation effects: The influence of urbanization on the production of emissions is discussed here. But doesn't the type of industry, the wealth of the population (lifestyle), etc. play a significantly greater role? Isn't there a big correlation between urbanization and population wealth? And isn't the explanatory variable more connected to lifestyle than to urbanism itself? Doesn't urbanization at the time of house construction itself have a significant effect on the production of emissions? And once it's built, these emissions don't happen again. How is this effect treated?

Answer: We redesigned the experiment and in table 6 we showed the results which treated PGDP, energy technology, and population as control variables. But there are still variables we can not put in the model such as lifestyle and house construction because lack of sample literature. That is a future research direction for us.

9.What is the quality of the regression model? How much does it describe the variability in the data? Is the degree of uncertainty (interval estimates) not too great? What is the indicative value (I don't mean statistical significance) of the results?

Answer: In subgroup meta-analysis such as the results in table 4, table 5 and table 7, we reported Q, tau2, I2 and H2 to indicate the quality. In Table 6, we reported R-squared, Wald, tau2, I2 and H2 to indicate the quality.

Incorrect description: "Figure1. Funnel Plot of Main Effect"

Answer: Thank you very much for your feedback and we have corrected it in the revision.

It is obvious that urbanization leads to the efficiency of processes (transportation, healthcare, education, GDP, etc.). Efficiency in the case of emissions production can also be assumed, which results from the efficiency of processes in society. E.g. the advantage arising from the scale in heating houses, etc.

Answer: The impact of urbanization on carbon emissions is clear in theory, but in practice, the conclusions are not consistent. The purpose this paper is to make the relationship between urbanization and carbon emission more clear in quantitative perspective.

What does the article conclude other than that urbanization is positive for emissions production? What did the results bring about something new? Where will the results of this article be useful? Do the results of this article have any real impact?

Answer: We discussed the contribution of this paper in lines 567-584.

Last but not the least, we want to thank you for your careful review of the paper, which very helpful for the improvement of the paper.

The authors

Author Response File: Author Response.pdf

Reviewer 4 Report

The readers of the journal, Sustainability, will find this a bold experiment in regression meta-analysis, with the specific environmental question not reaching a very useful conclusion. The methodology is to be appreciated, taking a broad view of research projects and screening them for a number of unintended biases. That critique draws attention for readers to the need for an objective and skeptical perspective when studying specific research reports on subjects close to the journal core interests.

The term “carbon emissions” is unambiguous but measuring the impact of “urbanization” through spatial-temporal differences does not leave a clear picture. As the authors concede, that impact has “multiple dimensions” (Line 34). In general the term ”urban” covers different meanings in different societies. In Chinese language the noun for “city” (shi) leads to confusion in Western culture. As an administrative classification “city” is very broad and can include expanses of farmland and even deserts and forest. Some Chinese provinces (eg Shanxi) consist of solely a number of cities. If the data used in this article treats urbanization as a function of population density or as related to carbon-emitting industrialization it is not clear to the typical reader. Suggest the authors make this clear.

The paper is well written and thought provoking for statisticians but I remark that policymakers hoping to improve the environment will not find satisfaction in the conclusion that the strongest impact of urbanization is in the eastern region of China.

It was disappointing to realize the 15 selected literatures were not cited in the References. Presumably they are listed in Supplementary Material.

The spelling, grammar and punctuation is all correct with exception that the 4 references cited Line 58 have no separation spaces.

Author Response

Dear editors and reviewers,

1.The term “carbon emissions” is unambiguous but measuring the impact of “urbanization” through spatial-temporal differences does not leave a clear picture. As the authors concede, that impact has “multiple dimensions” (Line 34). In general the term ”urban” covers different meanings in different societies. In Chinese language the noun for “city” (shi) leads to confusion in Western culture. As an administrative classification “city” is very broad and can include expanses of farmland and even deserts and forest. Some Chinese provinces (eg Shanxi) consist of solely a number of cities. If the data used in this article treats urbanization as a function of population density or as related to carbon-emitting industrialization it is not clear to the typical reader. Suggest the authors make this clear.

Answer: Thank you for your advice. We clarified the concept of different types of urbanization in table 1.

2.The paper is well written and thought provoking for statisticians but I remark that policymakers hoping to improve the environment will not find satisfaction in the conclusion that the strongest impact of urbanization is in the eastern region of China.

Answer: Thank you for your advice. According to other reviewers we redesigned the experiment and the coefficient was changed. And we re-discussed the spatial differentiation effects in lines 384-413.

3.It was disappointing to realize the 15 selected literatures were not cited in the References. Presumably they are listed in Supplementary Material.

Answer: We recited all the studies in the revision.

4.The spelling, grammar and punctuation is all correct with exception that the 4 references cited Line 58 have no separation spaces.

Answer: Thank you for your advice. It was corrected in the revised edition

Last but not the least, we want to thank you for your careful review of the paper, which very helpful for the improvement of the paper.

The authors

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

my comments has been included in the revised version

Reviewer 3 Report

The authors have answered the comments sufficiently and in great detail. I consider the revision of the text to be sufficient.

Reviewer 4 Report

I have reviewed the improved version and am satisfied with the changes. The ambiguity in the term "urbanization" has been rectified.