General remarks

As described in the title, the authors made an excellent review and analysis of the drained organic forest soil site-specific EFs from boreal and cool temperate regions, aiming to review current Tier 1 default emission factors (EFs) provided by the IPCC (2014) Wetlands Supplement.

Even if the results were only modest and did not change much compared to the Tier 1 default EFs, the authors are to be complimented for this extensive work as it is a timely and very informative research in the context and preparation of next IPCC reports and UNFCCC NGHGIs revisions. I personally find this synthesis of great added value, not only for the scientific modelling community but also for the national inventory representatives. Such studies are highly needed in the context of reconciliation between reported and observed GHG estimates, and this is one great example of work combining the IPCC and scientific methodologies, and hopefully more such reviews will follow, not only for the LULUCF sector.

These results could be used to complement the Tier 1 reported estimates with higher Tiers 2 and 3 used by BU and TD modelling methodologies, to improve and provide a more accurate picture on actual emissions.

Specific remarks

I would also add in the abstract and/or introduction information about the management status of the selected study-sites: are all managed sites, according the IPCC definitions (it is mentioned in the 2.1).

Line 57: The authors wrote “Wetlands characterized by organic soils (we hereafter use ‘wetlands’)”. I only found “wetlands” mentioned in the first two paragraphs of the Introduction. I personally think this is not needed, if else, please explain what was intended

Line 59: I saw in the table of figure 1 that few sites from the UK are also present, please add UK to the list of countries. I am somehow surprised that UK does not contribute more to this study.

Line 71: the authors list the processes, I would add that all these lead to enhanced (GHG) emissions

Line 78: did the authors check as well the 2019 IPCC Refinement (Chapter 7, Wetlands) for updated EF methodologies ?

Line 160: do you only refer to “b) comparability of CO2 EFs” ? how about CH4 and N2O EFs?

2.1 Criteria for data selection paragraph: it is appreciated that authors follow the site section as defined by the IPCC

Title 2.4: perhaps authors meant “different”

Line 369: I would delete the last words “in this study”

Line 373: except for a removal

Line 377: except for the typical ..

Title 3.3: pretty long, I would add a comma after weather and delete “and”

Line 447: How about correlations with WT and soil temperature? I saw the WT is discussed in paragraph 4.1 but I would add it here as well

Line 476: “This may be explained by the WT that, unfortunately, was not so generally available in the publications that it could have been used in the models” I would mention about this in the 4.4 data issues

Line 498: I totally agree that more research is needed regarding management sites. In the IPCC methodologies, only managed land is reported, therefore almost the entire EU is considered managed.

Title 4.2: perhaps authors meant “different”

Line 540: do authors know if this land was previously fertilized and for how long? Since how many years is afforested ??

Title 4.3: the title is ab it long, perhaps remove the means vs medians and explain it in few lines within the paragraph: "in this section we compare the means vs medians of CO2 estimates from...."

Lines 633-639: as previously mentioned, perhaps good to add here the scarcity of WT information (from line 475)

Conclusions: as already stated in the general remarks, it is a very useful study with improved ranges of uncertainty

Table 1: I would also add in brackets the extensively used abbreviations from the main text (e.g., NuP, NuR etc.)