Review Comments by Experts on Second Order Draft of 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories (General comments)
Comment
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4880

VolumeChapterFromline

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ExpertResponse

Authors note

GeneralThe following comments concern only aspects of estimating changes in soilorganic carbon for cropland and grassland.

Roland Hiederer

Noted

4882

General1. Assumption that higher tier methods lead (automatically) to more accurate
estimates of changes in SOC stocks.
This is cannot be substantiated by the results of using various SOC models inthe scientific literature. The models depend very much on the set-up,
calibration and data. Models also show differences in estimated SOC stocks in
the region of the error given in Table 5.5 for FLU (11% - 17%). Even using
different run-up periods can introduce such uncertainties in the SOC C model
output. It is therefore, questionable, how the assumption that the use of higher
tiers would lead to more accurate data unless the input data and the model
parameters can be more accurately specified. At the very least the wording
should reflect that an improvement in the accuracy of estimates from with ahigher tier method depends on the availability of suitable and accurate data.

Roland Hiederer

Accepted

Agreed. The accuracy of higher Tier methods will depend on anumber of factors. With poor input data and calibration, inaccurate
predictions would be produced by higher Tier methods. However, it isimportant to note that the Tier 1 method ,as currently presented, has
signficant uncertainty associated with the reference stocks (78-210%of the mean values - Table 2.3) and the stock change factors (5-50% of
the mean values for croplands and grasslands - Tables 5.5 and 6.2). In
addition uncertainty would exist in the spatial allocation of activity
data. With adequate input data and calibration to the conditions overwhich a model is applied, the potential to derive more accurate andrepresentative data are possible.
General explanation of tiers should be included in the Overview
Chapter.

4884

GeneralThe introduction of a three-pool steady-state C model for Tier 2

Roland Hiederer

Noted

The new Tier 2 method is proposed as an option that compilers may
consider, but there is also another option using the default equations.

Comment
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4886

VolumeGeneral

ChapterFromline

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ExpertResponse

Authors note

The introduction of this model is not a refinement of the existing Tier 2
method, but a fairly radical deviation from the reasoning behind 2006 IPCC
Guidelines.
It raises several questions and concerns:a) The Refinement text states that the 3-pool steady-state C model as a Tier 2
does not represent a Tier 3 model.
One may argue and disagree with this statement.
The steps and calculations are a cut-down version of the Century model, which
is a Tier 3 method.

Roland Hiederer

Noted

Note that the Tier 2 model in the 2006 guidelines is still provided in
the refinement, and therefore the new method is not refining theprevious method. It is an update providing a second option. The
proposed Tier 2 method is of intermediate complexity between Tier 1
and 3 methods. It allows a country to estimate C stock changes in amore disaggregated way compared to Tier 1, but lacks the complexityof a fully dynamic Tier 3 model. The equations provided can be used
to derive national C stock change factors that integrate C input andmanagement effects analagous to the default factors in the Tier 1
method. However, the Tier 2 equations allow the compiler to derivestock change factors that are more specific to their national
circumstances given the management, climate and soil conditions in
the country. This approach is analogous to the Tier 2 method inVolume 4, Chapter 10 for enteric fermentation, in addition to the stock
difference method for biomass that requires more detailed calculations
to estimate biomass C stock changes. The model differs from typicalTier 3 methods for this source category in that the results represent
steady state conditions and thus does not yield a fully dynamic timeseries by simulating water dynamics, temperature regimes, nitrogendynamics, plant production, and other processes that produce daily ormonthly estimates of the soil C stock changes. Also, it has been
decided to only provide this alternative Tier 2 method for Cropland
Remaining Cropland based on another comment.

Comment
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4888

VolumeGeneral

ChapterFromline

To lineCommentb) Going all the way to find the data for the various aspects of the proposedmodel one may well just use Century.
Going all the way to find the data for the various aspects of the proposedmodel one may well just use Century.
It is then superfluous to have this option as a Tier 2.It is then superfluous tohave this option as a Tier 2.

ExpertResponse

Authors note

Roland Hiederer

Rejected

The proposed Tier 2 method has been structured to minimise datarequirements. Generic global model parameters values have beendeveloped through application of a Bayesian calibration process (seeAnnex 2A.3) and are provided for the compiler in Table 2.3C. The
data required by the user to run the model is much reduced from that
required by Century and other dynamic soil carbon cycling models(e.g. RothC). Specifically, the steady state model requires spatial datafor climate, annual carbon inputs based on national yield data or
forage production (for which equations are provided) and organic
amendments, tillage practices, irrigation management and sandcontent. If a country does not have access to these data, much of thisdata can be obtained from global datasets, which are referenced to thelocation of these data sources is provided in the text. It is noteworthy
that the Tier 1 method also requires more activity data on management
than the Tier 2 steady state method. A Tier 3 model, such as Century,
requires some of the same data, such as climate soil types, irrigation,organic amendments and tillage practices, but information must bescheduled in the simulation on a monthly basis (or sometimes daily
basis) as well as the need for monthly data on mineral fertilizer
additions, planting and harvesting dates, fires, organic amendments,
crop types and sequences, harvesting practices, among other practices.
Moreover, the Tier 2 model has approximately 30 parameters, and thevalues are provided in the guidance. Century or similar models have
100s to 1000s of parameters that influence processes from the amountof maximum plant production, to leaching rates of carbon andnitrogen, overland flow of water, temperature regimes in the soil,
uptake of nutrients by plants, etc. The additonal complexity inparameterizing a typical Tier 3 model is many orders of magnitude
more difficult than the Tier 2 model provided in this guidance. Of
course, successfully calibrating a Tier 3 model is likely to generate
results with less uncertainty. This is another reason why the steadystate model proposed here at the Tier 2 level is not considered a Tier 3
model, which we would expect to provide results with less uncertainty.
Also, it has been decided to only provide this alternative Tier 2 method
for Cropland Remaining Cropland based on another comment.

Comment
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4890

4892

VolumeChapterFromline

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ExpertResponse

Authors note

Generalc) With the introduction of the model in the Guidelines may be seen as
endorsing the Century ecosystem model as the preferred model for estimating
SOC stocks and changes.
A more balanced view of the merits and limitations of various SOC models
would have been more appropriate.
This is addressed, but under Tier 3 (Box 2.2E).
Giving these examples for a Tier 3 m3ethod is better option than tacitly
proposing the method used by Century as a Tier 2.
For Tier 2 the choice of model should be left to the party reporting the data andnot be biased by the Guidelines.

Roland Hiederer

Rejected

The Tier 3 section does not endorse any specific process-based model.
Ultimately, the compiler must parameterize and evaluate a Tier 3
model for their national circumstances. The Tier 2 method with global
default parameters is a much simpler representation with intermediate
complexity than typical Tier 3 models. This model was proposed
because the steady-state solution was peer-reviewed and published in
the scientific literature. In addition, the Century model has been usedbecause of its extensive testing across a range of land uses, land usechanges and management practices being considered within inventory
analyses. Providing this Tier 2 option will allow compilers to improvetheir inventory without all of the complexity, time and resources
needed to develop a Tier 3 approach. However, it is likely that acompiler can develop a Tier 3 method and improve their inventory,
and this guidance does not endorse any specific model for Tier 3,
which may even be a measurement-based approach.

Generald) Introducing the model deflects from the need of all models for measured
data.
Assuming that the use of a model would increase the accuracy of estimates ofchanges in SOC stocks is flawed.
It depends very much on the quality input data and setting appropriate model
parameters.
One would have wished for a proposal for national soil inventories and support
to long-term experimental sites, i.e. expanding Section 2.5.1.

Roland Hiederer

Accepted with We accept that measurements are an important source of information
modification for an inventory. The proposed approach uses spatially explicit
climate data and inputs of carbon to soil along with a set of calibrated
global parameters. Applying this method with the global parameter set
will provide more specificity in the C stock change factors, comparedto the default equations that provided a limited number of bins for
estimating changes in C stocks (e.g., high, low and medium input).
This approach could be part of path for compilers to improve theirinventory in the short term before developing a more complicated Tier
3 method, which depends on adequate measurements. We agree that
quality of input data and parameters are critical for reducing
uncertainty, and there are limits to reductions in uncertainty given thatcompilers will be using global parameters with this Tier 2 option.
However, the guidance encourages Tier 3 methods if data are available
for developing these methods; see Figure 2.4 in Chapter 2 of Volume
IV. If data are available, compilers can optimize parameters and test
any model that they select, potentially further reducing uncertainty intheir estimates of soil C stock changes with a tier 3 method. The
development of a soil monitoring program would be desirable going
forward to develop Tier 3 methods with less uncertainty. Including thisTier 2 method in the guidance does not limit a compilers ability todevelop the Tier 3 method, which is encouraged by the guidance andwill require collection of soil C measurements.

Comment
ID
4894

VolumeChapterFromline

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ExpertResponse

Authors note

General

One may be forgiven to fail to see the introduction of the 3-pool steady-state cmodel as a refinement or improvement over the 2006 IPCC Guidelines.
It puts the virtualization of environmental conditions at the same level asmeasuring these conditions. This may be applicable in cases where conditions
cannot be measured, in particular when modelling scenarios as a what-if
condition.
However, the IPCC Guidelines concern past developments and reporting on
those developments, for which a modelling approach should take second place
to measurements.

Roland Hiederer

Noted

In principal it is agreed that where possible measurement should be theprimary focus of government resources for improving their soil C
inventory. However, few countries are implementing a measurment
campaign to derive national soil carbon inventories. The proposed
approach uses spatially explicit actual past climate data, inputs ofcarbon to soil based on national yield statistics, and mapped soil data
to estimate C stock changes. Using these data allows the Tier 2
method to approximate soil C stock changes based on past history.
Regardless, the method is only of intermediate complexity and there iscertainly improvements that can be made with a Tier 3 method, which
will require soil C measurements.

4896

GeneralIn this respect the 2006 IPCC Guidelines had a mopre balanced and measured
approach.
One could have understood a re-definition of the tiers into:
Tier 1: default values and static steady-state models.
Tier 2: dynamic models
Tier 3: inventories
May be a future amendmend to the Guidelines will rectify the direction taken
for reporting emissions and removals.

Roland Hiederer

Noted

This is an interesting suggestion and could be proposed in the next
refinement of the guidelines. In particular, differentiating processbased modeling and measurement based inventories (which are now in
the Tier 3 method) may lead to more specificity around these two very
different approaches to an inventory.

8348

GeneralI find it a very dubious procedure that comments are not possible on the textthat is not subject to refinement. I certainly found one or two mistakes there inlooking at the FOD. This is not providing the rigorous review expected of an
IPCC report.

Pauline Midgley

Noted

In accordance with the decision by the IPCC (Decision IPCC XLIV-5),
this report is not to fully revise the 2006 Guidelines. The authors are
not allowed to change the text where "no refinement" is expected in
the approved outline, unless changes are necessary to ensure
consistency with refinements made in the other parts.

1190

GeneralAccuracy. As long as it is understood that "accuracy'' of NGHGI means both
low bias and high precision (low uncertainty), then attention should be given
throughout the GLs that this term is used consistently. As an example, section
1.3.2 Of Col 4 Ch 1 (not revised), states that ''In general, moving to higher tiers
improves the accuracy of the inventory and reduces the uncertainty.''
According to the GLoassary definitions, it should actually simply say '' ...
improves the accuracy of the inventory.'' In fact, exactly because this IPCC
definition of accuracy (whihc coincides with the current ISO definition) is not
generally aligned with common use, one could atually write ''... improves theaccuracy of the inventory, that is, reduces bias (improves truness--to use a ISOterm) and increases precision.

francesco nicolatubiello

Accepted

Comment
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1206

VolumeChapterFromline

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ExpertResponse

Authors note

GeneralUse of Tier 2/3. This is of course what good practice is, however, as indicatedby every single figure in these GLs, the use of tier 2/3 is subject to the actual
availability of data--hence it depends on a country capability. I think this shoul
dbe conveyed as a message throughout teh GLs, becasue the result of thislanguage ofte has been that countries produce no inventory at all rather thanstarting with Tier 1--since they understand it is not good practice.

francesco nicolatubiello

Noted

Also, the 2006 GL are already very clear (see Overview chapter page8) that use of Tier 1 can be considered good practice depending on thecircumstances, and Volume 1 Chapters 1 and 8 show thatcompleteness of coverage is a key part of good practice1252

GeneralAFOLU. In which sense does the ''Agriculture, Forestry and Other Land Use''terminology fits within the six IPCC land use classes that are the focus of""AFOLU"? On the one hand, the AFOLU terms seems to imply that''agriculture'' and ''forestry'' are land use classes, i.e. alongside ''other'' land
uses. And yet, ''agriculture'' and ''forestry'' are clearly not IPCC land use
classes. Note nonetheless that ''agriculture'' and ''forestry'' are in fact land use
classes in the existing statistical classification followed by both FAO andUNSD as concerned. See for instance, the land use classification in the annexof SEEA AFF,
http://www.fao.org/fileadmin/templates/ess/ess_test_folder/Publications/Agrienvironmental/SEEA_AFF_White_Cover.pdf; or the FAO land use
classification, endorsed by the UN Statistical Commission, for international
reporting by countries to FAO on land use, irrigation and agricultural
practices: http://www.fao.org/economic/ess/ess-home/questionnaires/en/.

francesco nicolatubiello

Noted

The Sector title "AFOLU" was adopted and accepted by the IPCC in
2006. This report is not to fully revise the 2006 Guidelines, and should
ensure consistency with the 2006 Guidelines. It is our understandingthat the authors of the 2006 guidelines developed a name that would
cover agricultural cropland and grasslands, forest land and other land
uses (settlements, wetland and other lands). The intent was to unify
the previous agriculture and LULUCF sector, which subdivided
sources on land that often have interdepedencies throughbiogeochemical processes influencing GHG emissions.

1254

GeneralAFOLU (part II). Clearly there are internal definitional inconsistencies in theseguidelines that should be addressed. In the Glossary, ''land use'' is defined as anactivity that uses land. This is overall consistent with the definitions used by
the international statistical community, so that every single economic activity(as economic sectors) are associated to a land use class, including ''agriculture''and ''forestry''. Indeed, the most recent land use questionnaire by FAO talks ofAgriculture, Forestry and Other Land Use. However, the six land use
categories are not a one-to-one map to economic activities. Here at aminimum, the GLs should strive to at least indicate where ''agriculture''(cropland and grassland?) and ''forestry'''(forest land?) map onto.

francesco nicolatubiello

Noted

The terminology was adopted and accepted by the IPCC in 2006. This
report is not to fully revise the 2006 Guidelines, and should ensure
consistency with the 2006 Guidelines. It should be recognized that
this is not an economic-based classification, but rather a grouping
anthropogenic activities in order to estimate their influence on GHG
emissions.

Comment
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1256

VolumeChapterFrom
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Comment

ExpertResponse

Authors note

GeneralAFOLU (part III). It is understood that the AFOLU ''sector'' is not a sector in
the socio-econoic statistical sense, but only a part of the NGHGI as defined in
the 2006 IPCC GLs. It is also understood that ''land use'' emissions are only
those that are associated to changes in carbon stocks in biomass and soils aswell as associated changes in other GHG fluxes. A first recommendatoin is tochange the term ''sector'' to something more specific, such as ''inventory
sector''. This would avoid endless misunderstandings in discussoins at
UNFCCC about the ''land use'' sector in relation to mitigation via economic
activities, where in fact tehre is no such thing in the economy as a ''land''sector.''francesco nicolatubiello

Noted

The terminology and source/sink categorization was adopted andaccepted by the IPCC in 2006. This report is not to fully revise the2006 Guidelines, and should ensure consistency with the 2006
Guidelines. We agree that that this is not a socioeconomic term, butrather a classification to differentiate groups of activities in a country
for an efficient compilation of a GHG inventory.

1258

GeneralAFOLU (part IV). If the more narrow definition of the AFOLU ''sector'' inthese guidelines is accepted, then how can emissions from ''livestock,''
especially enteric fermentation, be a part of AFOLU? In this sense, it was
better to keep ''agriculture'' as a separate ''sector'' from FOLU. If the tentative
answer is that the methane bulched by cows comes from grass in the field, then
one could observe that many manufacturing activities generate emissoins
linked to land and thus should also be accounted for under AFOLU --which is
obvioulsy not possible.

francesco nicolatubiello

Noted

The terminology and source/sink categorization was adopted andaccepted by the IPCC in 2006. This report is not to fully revise the2006 Guidelines, and should ensure consistency with the 2006
Guidelines. Including livestock in this sector is important because thelinkages between livestock production and dependence on land forforage as well as impact on land with urine and manure return to soils.
These linkages are important for estimating GHG emissions from boththe land and livestock.

1260

GeneralAFOLU (final). The only part that makes sense in putting AFOLU together isthe recognitoin that a significant component of FOLU emissions is caused by''agriculture'' as an economic sector. This allows then for increased
consistency, i.e., to account within a unified place for non-CO2 and CO2
emissions coming from one single activity (e.g., drainange of peatlands). Yet
all of the inconsistencies mentioned above are not resolved by this useful
purpose.

francesco nicolatubiello

Noted

The terminology and source/sink categorization was adopted andaccepted by the IPCC in 2006. This report is not to fully revise the2006 Guidelines, and should ensure consistency with the 2006
Guidelines. Grouping activiities into sectors is useful for conducting a
GHG inventory. It may be possible to improve the classification in
the future but it is beyond the mandate for this report.

2574

GeneralPlease go through all chapters and correct all notations. At least I have found
four:

Steen Gyldenkærne

Accepted

This kind of consistency throughout the report was ensured to theextent possible. However, some inconsistenies might still remain.
Those will be rectified by TFI TSU before the final publication of thisreport, in accordance with the IPCC procedures.
However, it seems very difficult to achieve perfect consistency becausesome inconsistencies already existed here and there in the 2006
Guidelines.

GeneralTo line" yr-1" versus "year-1"" °C " versus "degrees C""fraction" versus "proportion"
denominations are some places provided in brackets "[ ]" or "( )"Shall references be "Volume (roman letters)" or "Volume (arabic digits)"?
"unitless" versus "dimensionless"Comment
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Comment

ExpertConsidering that FAOSTAT statistics are mentioned as an alternative source ofactivity data whenever national information is missing, it may perhaps help toinsert a Table summarizing all the available FAOSTAT data sources, at theoutset of this chapter or even at the outset of this volume (or as an appendix toit). To this end, kindly consider consulting as well as inserting a reference tothe IPCC (2015) report 'Emerging activities to combat climate change– use of
FAO data and IPCC GHG Inventory Guidelines for Agriculture and Land Use'
(https://www.ipcc-nggip.iges.or.jp/public/mtdocs/pdfiles/1411_FAO-IPCCIFAD_Rome_AFOLU.pdf ).

francesco nicolatubiello

Temperate, cold. This comment applies to the definitions of climatic zones inthis glossary. Are they consisten with how the same terms are used in other
IPCC Assessment Reports and more in general in the scientific literature? If so,
why can’t a link to where this definitoin comes from be given?

francesco nicolatubiello

Response

Authors note

Accepted with The Author's view is that FAO start is one of the alternative sources
modification for activity data amongst a large portfolio of international, regionaland national sources. Approaching the chapter in this way will meanequal treatment for other data sources. In response to the comment,
the Authors have enhanced the text on the use of FAO data chapters 2
and 6 of Vol.1 and included key references.

Noted

The climate classification in this guidance is used to derive emission
and stock change factors in the AFOLU volume. It is not feasible to
make changes in the classification at this point in the review process
because developing the new default factors requires a synthesis of theliterature that has taken 6-12 months for many of the author teams.
The proposed change may be possible in the next refinement if
harmonization of climate classifications is brought to the attention of
the IPCC experts during the scoping process before preparation of thereport begins.