General overview of the article

This paper presents a comparison of greenhouse gas (GHG) emissions—by species type—between EDGAR estimates and G20 submissions to the UNFCCC. I believe this represents a valuable contribution to the existing literature, offering insights into the reasons behind discrepancies between global emission inventories and national submissions. This topic is of interest not only to the scientific community but also to national inventory compilers.

Furthermore, the paper highlights the importance of global emission inventories in providing a more comprehensive picture of GHG emissions, particularly for regions where data is not regularly updated or readily available.

With regard to comments and suggestions for improvement, at a high level, I would suggest enhancing the clarity of the Introduction. The sample of countries considered is occasionally not well explained, and the rationale for selecting certain sectors to emphasise differences (e.g. Figure 1 and the associated analysis, which refers to all Annex I countries, some of which are not part of the G20) is somewhat unclear.

Another recurring issue in the Introduction is the assumption that readers are already familiar—or very familiar—with the methodology underpinning the EDGAR database. While this may be partially true, I believe the authors may be overestimating the extent to which the audience is acquainted with EDGAR’s methodological details.

I would also recommend enriching Section 5 with further reflection on the limitations inherent to global emission inventories. In its current form, the manuscript rightly emphasises the need for such tools and the methodological improvements made to enhance the EDGAR database. However, there are intrinsic limitations associated with global coverage that could be acknowledged and discussed, thereby offering readers a more balanced and comprehensive perspective.

As noted earlier, the paper presents insightful findings and constitutes a meaningful contribution to ongoing discussions on best practices for emission reporting, quantification, and transparency frameworks.

Below, the authors will find specific comments relating to individual sections of the manuscript.

Introduction

1. I would encourage the authors to consider rearranging some of the paragraphs in the Introduction. At present, the opening section informs readers of the differences between EDGAR and national submissions to the UNFCCC. However, it assumes familiarity with the methodology, species, regions, and sectors covered by EDGAR. While these aspects are addressed later in the text, reordering the paragraph flow could improve readability.

2. Lines 131–140: Although this may be evident to the authors or to part of the audience, I would recommend elaborating on the tier-level differences between EDGAR and the UNFCCC dataset.

3. Building on point 2: I cannot recall at present—are fuel carbon contents in EDGAR nationally or regionally representative? How does this compare with the UNFCCC dataset?

4. Continuing from point 2: How does the EDGAR database currently account for differing assumptions regarding waste disposal (e.g. landfills) and leaks associated with natural gas transport? Variations in emission modelling for these sectors could significantly contribute to observed discrepancies.

I appreciate that word count limitations and scope definitions may constrain the level of detail provided. Nonetheless, brief comments on the above aspects would help readers better understand the sources of divergence.

5. I find Figure 1 somewhat confusing, for the following reasons:

a. The paper aims to explore differences between EDGAR estimates and UNFCCC data for G20 countries. However, the figure appears to summarise methodologies for all Annex I countries. Is this correct?

b. It is unclear why the authors have chosen to focus on these two sectors. Is this due to their proportional contribution to total GHG emissions across G20 countries?

c. Would it not be more informative to indicate the methodology/tier level used by each of the 20 countries for the selected sectors?

d. When comparing methodologies, could the authors clarify which national communication cycle has been considered for the non-Annex I countries in the G20 bloc? And which submission year for the Annex I countries?

6. Could the authors explain their rationale for presenting median figures across the sample? Why is this considered more relevant than reporting total emissions for the group of countries? Is this due to missing data for non-Annex I countries across the time series? If so, is the mean still representative?

Global GHG emissions

7. The title of this section may be misleading, as the analysis focuses on G20 countries rather than global emissions. Please consider revising the section title accordingly.

Global CO₂ emissions

8. A similar comment applies to this section title. Since the comparison centres on G20 countries, referring to it as “Global CO₂ Emissions” may be inaccurate.

9. The authors note systemic differences for Italy, Japan, and others. While the percentage differences are relatively small, have the authors explored the underlying causes? Could these be related to activity data or assumptions regarding fuel carbon content? Have the authors identified which sector contributes most to these differences?

10. When discussing fugitive emissions, could the authors specify which part of the natural gas or oil production value chain is responsible for the observed differences? It seems unusual that this would account for discrepancies in CO₂ emissions, given that fugitive emissions are typically associated with methane. Are the authors referring instead to process-related CO₂ emissions from industrial sources? Please clarify.

Global CH₄ emissions

11. Again, the section title may be misleading given the focus on G20 countries.

12. Lines 573–581: Could the authors comment on the role of assumptions regarding the quantity of waste landfilled, waste composition, and methane recovery from landfills?

13. I would also encourage the authors to briefly explain the FOD method used for methane estimation or provide references for readers to consult. Comments on model calibration would also be welcome.

Global N₂O emissions

14. As with previous sections, the title may benefit from revision to reflect the actual scope of the analysis.

Section 5

15. I concur with the points raised by the authors. However, a deeper discussion of the limitations associated with global emission inventories—particularly the use of Tier 1 methodologies, the lack of local/national data on technology penetration, and the use of emission factors that may not be geographically representative—would be beneficial. Such additions would offer readers a more balanced and comprehensive understanding of the constraints inherent to global inventories.

General comments.

The paper compares EDGAR inventory of three major greenhouse gases to the national inventory reports, sourced from UNFCCC database, countries National Communications and Biannual Update Reports. The comparison is useful to inventory compilers, as 2006 IPCC Inventory Guidelines explicitly mentioned EDGAR as a source of independent data suitable for checking the estimates produced for National Inventory Reports (transparency reports in recent wording). The comparison uses G20 subset, which is justified by covering majority of emissions for purposes like global stock take. The paper is well written and can be accepted with minor revision.

Detailed comments

1. Suggest mentioning 2006 IPCC Inventory Guidelines (Vol.1, Chap 6) recommendation to use EDGAR and other global inventories as a part of the verification process.
2. Need to mention some examples of emission uncertainties for non-G-20, non-Annex countries, that are revealed by differences of emission estimates by different NIR releases, especially for N2O and CH4.
3. Would be interesting to have more details how “time series consistency” (term in 2006 IPCC Inventory Guidelines) is implemented in NIR/UNFCCC reports and EDGAR
4. Line 510-512 attributes source of activity data in EDGAR for fugitive emissions to IEA. The Table 1 below present the India’s coal sector CH4 emissions, it shows a drop after 2012, while country statistics on coal use don’t have exhibit such a drop. Can this change be attributed to IEA data or change in emission factors?

Table 1 EDGAR_2024_GHG estimates of India’s fossil CH4 emissions from solid fuels (including coal mining, coal storage; numbers truncated not rounded)

Technical corrections

Line 59 References Pfenninger et al., 2014, Prina et al., 2020 not found in a reference list.

References:

Emissions Database for Global Atmospheric Research (EDGAR), release EDGAR_2024_GHG (1970 - 2023) of October 2024.