Interactive comment on “Global Covenant of Mayors, a dataset of GHG emissions for 6,200 cities in Europe and the Southern Mediterranean”

Abstract. The Paris Agreement has underlined the role of cities in combating climate change. The Global Covenant of Mayors for Climate and Energy (GCoM) is the largest dedicated international initiative to promote climate action at city level, covering globally over 10,000 cities and almost half the population of the European Union (EU) by end of March 2020. The latest Intergovernmental Panel on Climate Change (IPCC) report denotes that there is a lack of comprehensive, consistent datasets of cities' Greenhouse Gas (GHG) emissions inventories. To address part of this gap, we present here a harmonised, complete and verified dataset of GHG inventories for 6,200 cities in European and Southern Mediterranean countries, signatories of the GCoM initiative. To complement the emission data reported, a set of ancillary data that have a direct or indirect potential impact on cities' climate action plans were collected from other databases, supporting further research on local climate action and monitoring the EU's progress on Sustainable Development Goal 13 on Climate Action. The dataset is archived and publicly available with the DOI number https://doi.org/10.2905/57A615EB-CFBC-435A-A8C5-553BD40F76C9.


If one would only read the abstract, it would perhaps expect a detailed analysis and description of a GHG emission dataset from cities, in the context of the current Paris Agreement and European emission reduction targets, and this is exactly what I was expecting. However, reading the whole paper, I have the feeling that it misses some substance in the actual meaning and use of this dataset.
Even if I understand that this is a dataset description paper and I should not expect much scientific results, somehow I was a bit disappointed not finding the real aim and scope of this study.
My point is, it is an interesting work but I was looking forward to find something about the actual results reported by these 6,200 cities, what is their current state in terms of GHG emissions, and how are they doing in the reporting process and Paris Agreement targets. This is not more than a methodological/abstract statistical paper which, in my personal opinion, would greatly beneficiate of a section summarizing the actual data presented by this dataset. It will give the general audience more insight into what actually this database is about -GHG emissions from cities.
For example one could present 1) a classification of top 10 emitters cities/large areas (in CO 2 eq or kton gas) and their percentages with respect to the European GHG total emissions highlighting sectors and activities responsible for these emissions (useful for local mitigation strategies); 2) look at emission trends observed between the baseline year (1990) and last available year (2019)? 3) How do local governments make use of this data? Also, authors do not mention other initiatives like e.g. C40 cities.
Overall, I think this paper will be of great interest to all policy/science/industry users and, therefore, I encourage authors to put a little effort and if possible restructure and combine this methodological abstract description with an overview of scientific results.
The manuscript would also beneficiate of a native English speaking review. Therefore, I suggest major revisions and I am really looking forward to an improved version of this manuscript.
Below are my comments which hopefully will be appreciated and help in improving the manuscript, followed by a list of line-by-line specific changes: I miss at the end of the title a word, could be cities or countries? I accessed the online database (with more than a click, ESSD data policy states one click to download the data) and I see "countries" after Mediterranean. I would strongly suggest to add it as well to the title. In general throughout the manuscript, terminology is not always explained. Readers not familiar with this background need to clearly understand the terms and acronyms. Consistency in using acronyms and dataset names is poor. Since the beginning of the paper I stated to get confused by the use of GCoM and CoM, the authors should be consistent and use, in my opinion, only GCoM (online tables as well). I also miss references for many products. Transparency is the key to such data description papers and links to guidelines and regulations need to be provided. I strongly recommend the introduction of a Figure 1 to define boundaries and study area. Will be helpful to visualize the countries/cities. I somehow can't access the Supplementary files by clicking on the link in the manuscript. I could only view them from the preprint ESSDD website. The authors compare GCoM results with EDGAR v5.0 dataset (should be specified everywhere in the manuscript that authors used EDGAR v5.0) They state that "Overall, considering the completely different origin of EDGAR and CoM primary data the agreement has to be considered fully satisfactory". I personally think that a low uncertainty of two completely different datasets could either imply that both are good or that both are bad. Authors should explain better the methodology used to calculate uncertainties (perhaps add it as an Annex).
Specific line-by-line comments: L3: Title: add "countries" after Mediterranean L15: Please specify here and throughout the paper what EU are you referring to, I guess it is EU27.
L16: which latest IPCC report? Please add year and reference L17: should be "emission inventory" L17: I would reformulate: "To partly address this gap, we present a harmonized..." L18: what do you mean with complete and verified dataset, please explain in a footnote "complete and verified" As far as I understood, it only contains the three main GHGs (CO2, CH4 and N2O) what makes it complete?. To be mentioned, since the beginning, that you only report these three GHGs.
L19: "to complement the reported emission data" L21: I would call them datasets (and not databases) L22: EU (without 's) progress on the Sustainable Development Goal (SDG) 13 on Climate Action (I would add a reference here) L22: "The datasets ..." please check the font size and note that this link does not work. Replace it with the one from the Data Availability section or references https://doi.org/10.2905/57A615EB-CFBC-435A-A8C5-553BD40F76C9 Actually, the ESSD data policy states that access to data should be done with one click, I already clicked 3 times to download the data. L25: I would delete Summary L27: Perhaps authors could find a more recent reference? L31: dot at the end of the sentence.
L35: authors state that there is an absence of a global cities datasets, true but other initiatives (e.g. C40 cities) should be mentioned.
L39: "gaps for Europe". In the beginning the authors were talking about EU, now is Europe, please use consistent domain.
L40: Mediterranean countries: on L61 is written cities: the authors should be consistent in using the same name of this dataset e.g. countries everywhere.
L41: now we have again EU, before was Europe. The Southern EU neighborhoods are the same with the Southern Mediterranean countries? Why not simply EU27 +UK and Western Balkans (I guess non-EU)? What countries are part of the EFTA?
As I already mentioned, this paper would really beneficiate of a figure with the study domain, cities/countries. L49: delete space after neighborhood. It is very abstract, can you please define on the map all these groups? (EFTA, W Balkans, EU27, Eastern and Southern neighborhoods?) L51: mention that in 2008 we had EU28; please add parties or signatories after 10,000.  Perhaps the authors could present in the introduction some more information on the other platform, CDP-ICLEI Unified Reporting System, why these two platforms? what are the commonalities and differences with My Covenant, why cities should report to one or another?. More insight into methodologies governing these two platforms should be mentioned as well.
L122: The Common Reporting Framework (CRF) is a little bit misleading. CRF is an official terminology used under the UNFCCC reporting, the tables are named Common Reporting Format, can you please specify in a footnote that CRF is not linked to the UNFCCC process? Readers not familiar with it would think are the same tables. L133: replace "they also can report" with "they can report as well.." and who are they? Cities, inventories, protocols? In the Description column, please use capitals for ETS, and delete double spaces. Would be useful to add in the caption which GHGs are we talking about.
In general, all captions from this study are very short and not fully explanatory.
Waste: to my knowledge, waste sector and activities should be numbered with 5 (5A, 5B etc.).
L146: The geographical boundaries definition: should be mentioned before, on L127 L147: "regarding the type of gases" they should be detailed before in abstract and introduction L149-150: there are two GWPs largely used depending to which IPCC AR report you refer to, AR4 uses 25 and 298 for CH4 and N2O respectively (and countries report them to UNFCCC CRFs ) and AR5 28/34 and 265/298...which ones are you using??? please define as well GWP in a footnote, you use the GWP 20 or 100 etc. Is it "had been" the correct tense? these complete inventories were submitted and will never be submitted again? Or could be "have been submitted" because they still exist in present times?
L173: SECAP appears already at L69, please describe there what it is (add footnote with a link to it if possible) L174: add comma after available L175-178: these two sentences are repeating, can you please merge and make one sentence? Correct with "reported data, GHG emissions" L178: replace with: Figure 2 shows the frequency distribution of 2019 GHG emissions per capita from emission inventory datasets, .." L180-183: Could authors please rephrase the explanation for Figure 2? I don't really understand the density here and what exactly is intended with this figure? What is the width of the class, where was defined? Are too many i.e. which interrupts the readability of the sentence. L200: please add after: waste sector, see Table 1) L218: 2.2 as mentioned before, this section is also about detection of outliers from large urban areas, for a better flow of information I would: -rename the section as "detection of outliers from large urban areas" -add two subtitles Activity data and Emission factors.
L225: Eurostat database, please add version, year, reference. L225: I think is "are classified as" L232: please name some EU statistical systems L233: "In case of reported data that ranges out of" L234: "accuracy of the platform's reported data" L237: "have been manually corrected" L238: "therefore, we assume as valid the data reported in the SECAP document." L243: IPCC AR4 (and reference) perhaps add a link to a chapter annex etc.
So, this means that you are using AR4 GWP values as well? see my notes on line 149, define it there please. L249: rename with: detection of outliers from small medium towns (see also comments on lines 108-115) I would add here as well Activity data and Emission factors sub-sections to separate better the discussion.
L264: I think CAP is with capitals and please define it. Again consistency needed throughout the entire manuscript with EU-ETS, or ETS only or acronym versus EU-no acronym etc. L265: could you please name these few exceptions in ( )? L269-274: Does this method is mentioned before on L202 as the rule to treat the outliers? Of yes, please explain it there.
L277 and everywhere else: should Supplementary files 1 and 2 be accessible with one click from the text?
L282: Now we have a new name of the dataset: "CoM dataset 2019: Emission Inventories" Is this the same with GCoM datasets of 6200 cities from the title? Is this study about this dataset? Is yes, please clarify this in the beginning, as it creates really creates confusion. We have now CoM and GCoM and "CoM dataset 2019" only and "CoM dataset 2019-Emission Inventory" etc.
It actually appears on L78 but in this paragraph you state that hereafter you will name it as such.   L337: This paragraph introduces already the uncertainty subject before the comparison is actually discussed, I would first present the comparison and after discuss uncertainty.
L345: when comparing GCoM to EDGAR, how about proxies used by GCoM compared to those in EDGAR? Could you summarize them in a table? This will make a clear discussion on why these datasets are completely different.
L349: explain LAU please; delete "s" from emissions (EDGAR emission grids) L350: "and two source categories" delete for L351: "energy in buildings (RCO)". Where was this defined? I do not find this sector in In this paragraph also subscript for CO 2 L358: before on line 352 you used RCO, please be consistent, also with capitals (energy vs Energy) L367: here you use " " for the Energy in building(s) sector, and singular for building L367: is there a methodology for uncertainty calculation and what exactly this uncertainty represents? Very low values given that datasets are so different L368: whereas without capital W L372: "emissions in the Covenant framework cover" L375: "emissions" L376: Further limitations are discussed in the next section L377 paragraph: I would still like to know more about the methodology used to calculate uncertainties L390: I would use Secondly, You state that "there is a limited knowledge on the methods by cities in determining the emissions..." this is exactly why methodology should become mandatory to GCoM submission system, parties must offer transparency when calculating their emission stating the guidelines, methodology and protocols they use.
L393: Can you please explain here the word "modeled" ? I am a modeler and I am familiar with the EDGAR database since a long time, I would not name it modeled, It calculates emissions as EM = AD x EF a simple global Tier 1 consistent approach for all countries, but not modeled.
"whereas EDGAR calculates emissions following a consistent Tier 1 approach based on AD and EF country specific information" L393: replace suppose with assume L393: based on collected activity data L394: Replace Indeed with: "For these areas, there is a good match ..." L397: Please replace modeling exercise with "emission calculation methodology" L408: delete "also" L408-410: Will be of great interest to find out more about CDP-ICLEI platform and I am still interested to know why are two systems and how do they differ. L421: our colleague; replace deep reviewing with "in-depth review"