the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Annual emissions of carbon from land use, land-use change, and forestry 1850–2020
- Woodwell Climate Research Center, 149 Woods Hole Road, Falmouth, Massachusetts 02540, USA
- Woodwell Climate Research Center, 149 Woods Hole Road, Falmouth, Massachusetts 02540, USA
Abstract. Estimates of the annual emissions of carbon from Land Use, Land-Use Change, and Forestry (LULUCF) are important for tracking global, regional, and national carbon budgets, which in turn help predict future rates of climate change and help define potential solutions for mitigation. Here we update a long-term (1850–2020) series of annual, national carbon emissions from LULUCF (Houghton and Nassikas, 2017), based largely, after 1960, on statistics of land use from the Food and Agriculture Organization (FAO) of the United Nations (Faostat, 2021). Those data suggest that rates of deforestation in the tropics (and thus net emissions of carbon) have decreased over the last ten years (2011–2020). The data also indicate that the net loss of tropical forests is greater than the net gain in croplands and pastures, and we explore three alternative interpretations of this apparent forest conversion, one of which is shifting cultivation. We note that LULUCF is not equivalent to LULCC (Land-Use and Land-Cover Change), and suggest that the difference between “land use” and “land cover” may contribute to variation among independent estimates of emissions. The calculated emissions of carbon based on LULUCF approximate the anthropogenic component of terrestrial carbon emissions, but carbon management opportunities exist for unmanaged lands as well.
Richard A. Houghton and Andrea Castanho
Status: final response (author comments only)
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CC1: 'Comment on essd-2022-351', Francesco N. Tubiello, 18 Nov 2022
This is an impressive piece of work which extends current estimates made with bookkeeping models. At the same time, there is a need to significantly refine the interpretation of the FAO statistics which are used as input into this study--with implications for results as well as wrt how uncertainty should be communicated.
I hope you don't mind if I have made comments directly within the original manuscript in pdf. Attached is Part I of my comments, from Abstract to just before the Discussion section.
- CC2: 'Comment on essd-2022-351', Francesco N. Tubiello, 21 Nov 2022
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RC1: 'Comment on essd-2022-351', Anonymous Referee #1, 01 Dec 2022
This manuscript describes a dataset of carbon emissions from historical land use, land-use change, and forestry, presented nationally, regionally, and globally. The dataset is an update to a previously published dataset, and incorporates new data from FAO, along with new model assumptions and processes. The paper is well-written and presented logically.
In addition to describing the specific details and improvements of the dataset, the manuscript has a great description of the many sources of uncertainty in datasets of land-use and related emissions, both generally and for this particular dataset. Specifically, the authors explore how to use and interpret the data from FAO that indicates the area of tropical Forests Converted to Other land (FCO). They employ three alternative interpretations of FCO, with shifting cultivation being the default assumption, and compare the modeled results of each assumption. This is a valuable discussion, along with the discussion of uncertainty in land-use emissions that arise from limitations of limitation of satellite data, and uncertainty that arises from alternative definitions of land-use change emissions and which processes are included.
Overall, this manuscript provides a good dataset description and also provides an excellent discussion of land-use emissions and their related uncertainty. I have a few comments and suggestions for the authors (listed below) but otherwise recommend it for publication.
- The apparent mismatch between net loss of tropical forest and the net increase in cropland and grazing land is described as “forests converted to other lands”. However, perhaps it is also possible that the forest, cropland, and grazing data provided by FAO are just not consistent with one another, and that the differences between net forest loss and net agricultural gain represent the uncertainty or error in the reporting of land-use data to FAO? The reporting of data to FAO also happens infrequently (I think every 5 or 10 years) so it is also possible that the timing of changes in the various land-use categories are not being reported on the same time scales. Has this been considered by the authors?
- Why were changes in fire management considered in the model for only the USA and not for other countries?
- Why did the area of secondary land used for wood harvest increase in this version of the model code? (Section 2.3.1 and Section 3.1). I can see that this would make a difference to the recovery (and gross uptake of carbon) but it wasn’t clear in this section why this change to secondary wood harvest areas had been made in the first place.
- Line 406: the cited publication (Friedlingstein et al. 2022) is for the 2021 Global Carbon Budget not the 2020 global carbon budget.
- Fig 1: the lines are very thin and hard to read
- Table 1: what is meant by the “peat-2020” column?
- Fig 2: the gray lines and black lines and mostly indistinguishable on my screen
- Fig 3: are the region labels used in this figure (and elsewhere in the manuscript) defined somewhere?
- Fig 4: lines are too thin, black lines look gray
- Figs 1, 2, and 4 present similar information, although each is slightly different in order to compare specific changes to model assumptions or data. It would be helpful if the figure captions could more clearly capture or describe the intended message that each figure is trying to convey, to help separate these figures from each other for the reader. In addition, some of the lines in these figures have the same legend labels (e.g. “this study FAO 2021 recovering”) but show different data. Is that because some of these figures include emissions from peat, while others don’t? Or is there another reason for these differences?
- Table 2: the caption indicates that emissions for 2 different time periods are included (2011-2020 and 2011-2015) but the later doesn’t appear to be shown
- Figure 9: the figure shows emissions from different types of land-use. However, it is not clear if “crop” or “pasture” are emissions from the use of that land or the land-use conversion from some other land to cropland or pasture (which would be a land-use change).
- Figure 10: font is too small to read
- Table 4: I have the same question as above r.e. types of land use. Also why are some (many) numbers bold?
- Figure 13: the lines are very fine and difficult to read
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RC2: 'Comment on essd-2022-351', Anonymous Referee #2, 06 Dec 2022
This work updated the emissions made by bookkeeping models by Dr. R. A. Houghton and colleagues by using updated land use data from FAO by considering three alternative explanations of excessive forest loss compared with increase in agricultural lands by FAO.
This work is without doubt worthy for publication in ESSD as it is a core dataset underlying the annual global carbon budget made by the Global Carbon Project. But at the same time, I have quite some comments and thoughts which I take chance to discuss with the authors here, which I hope the authors can consider while making revision.
Major comments:
- The bookkeeping approach has been well developed. Because it is a bottom-up approach based on the idea of quantifying anthropogenic effects only, there are no large-scale independent observations to validate this quantification. Despite this is an update that the authors tried their best to make, however, it is also the improvement against which we have no objective standard to benchmark that gives us a chance to verify such an improvement. I think this point needs to be made clear in the paper so that people understand this
- Related to the comment above, I think the core contribution of this paper is to enhance clarity and provide a one-stop information hub for this dataset and the associate methods, datasets used. The bookkeeping model has a long history (the earliest version was in 1983?). I think it would be useful to make this current paper long but it can be used as a full reference to understand the details of this dataset, so that people don’t have to check very often Houghton & Nassikas (2017) and when they refer to that paper, the readers were furthered referred to some earlier papers. Some information, for example, the carbon densities used for different vegetation types, their response curves, could be repeated in the Supplement but they will be useful. It is very important to have this kind of one-stop information hub for this method.
- For the sake of clarity and traceability. An exact of cross-walking table from land use types in FAOSTAT to the land use types in this study and the associated assumptions need to be provided. The authors simply cited FAOSTAT, 2021. But when readers go to the webpage, it is really unclear which information has been used and how the land cover types were interpreted into the land use types used here.
It has to be made explicit that all land use transitions reported by FAO are considered anthropogenic although this assumption is very difficult to verify.
- The nomenclature or terminology used is sometimes confusing and vague. The most vague one is ‘degradation’. The whole block of discussion centering on ‘forest degradation’ (section 4.2.2) is based on an *undefined* term of ‘forest degradation’. If the terminology cannot be clearly defined and made consistent among different studies, comparing different studies won’t make things clearer.
- What made the authors believe that the adjustments made in section 2.3.1 are necessary and indeed are close to the real world?
- Will the authors consider making available the underlying data, e.g., areas of different land use types, carbon densities for different land use types, key parameters for response curves? I believe there are wide interest in using this information from the community.
Minor comments:
There seem many of them, but most are demanding clarifications.
Line 36: So what is the difference between LULCC and LULUCF? The readers are expecting explanations but then there are no further explanations. Perhaps lines Line 475-477?
Line 50–52: wood harvest is a form of land use but not land use change. If this is the case, then it is not the difference between LULCC and LULUCF? I think the authors are free to choose the name they like but without the explanations that are expected in my previous comment, confusion starts to arise here.
Line 74-76: I don’t understand the reason exactly. The reasons listed in the brackets are still vague. Could the authors clarify on this?
Line 114-115: I understand FRA is published every 5 years and the author used FRA2020 to derive change rates for 2015–2019 but they assumed the same rate for 2020. Detailed descriptions would be better. If my understanding is wrong then it justifies the need of detailed descriptions.
Line 110: Since FAOSTAT 1960 every year the national areas of forest were reported but in lines 62-63 it says the forest area information was not used until 1989. Is my understanding correct? Maybe explain the reasons so that readers won’t get confused.
Line 143-145: I would suggest putting this information much earlier than here and maybe in the Introduction. This is a fundamental aspect that the readers need to keep in mind while reading the paper. Its scope is not limited to the title of this section.
Line 149-151: do these lines continue describing ‘degraded lands’? they are not easy to understand. What is the difference between ‘permanent croplands’ and ‘cropland’ introduced previously? Or you are describing ‘degraded croplands’ which seems in a transitional state between cropland and forest? (abandoned but not fully recovered to forest yet). ‘Degraded croplands’ should have higher carbon density than ‘normal cropland’ or ‘permanent cropland’? I think ‘permanent cropland’ is the most confusing term here.
Line 162: the thing described in this paragraph was called ‘shifting cultivation’ in Houghton and Nassikas (2017)? I am not sure I am correct. But if I am, then this is in conflict with the next paragraph?
I have another question here: In Houghton and Nassikas (2017, GBC) it says “We did not attempt to account for shifting cultivation in this analysis ”. So would be nice to explain that you accounted for this because in Table 1 there is such information. In your paper on GCB on negative emissions there it was clearly said shifting cultivation was included. So I guess either it’s a wrong citation or you just need to explain. Given the wide influence of your work in the carbon cycle community and the wide usage of this data, it would always be nice to be traceable as far as it allows.
Line 166: So what is the standard be counted as ‘deforestation’. If it is measured by decrase in carbon density, by my understanding the first class ‘degraded croplands ’ seem having a lower carbon density than ‘shifting cultivation’ and hence, conversion from forest to ‘degraded croplands’ should qualify ‘deforestation’ as well?
Line 163-173: Does this mean shifting cultivation has a strict rotation length < 5 years?
Line 181: what is this FCO?
Line 182: a small note explaining that the area of fallow of shifting cultivation was provided in FAO/UNEP (1981) and whether their definition is consistent with yours can be helpful for readers here.
Line 207: Here the fallow lengths are between 2 and 15 years but in Line 163-164 the fallow length is limited to 5 years by definition?
Line 210: need to describe what do you mean by ‘traditional shifting cultivation’, after all these lengths of descriptions of ‘shifting cultivation’.
Line 163: Need to warn the readers about its importance in this paper (i.e. the third interpretation) and briefly explain why, and then warn the readers that a lot descriptions will be devoted to this type so that the readers can be well prepared for the paragraphs that follow and will have better understanding (I hope). I say this basically because the words used for each type of interpretation are highly disproportionate.
Line 187-190: this comparison is really nice and informative. Thanks.
The title of section 2.3.2: might be useful saying directly which is the ‘new data from the FAO’ by being less ambiguous.
Line 227: “the results of the four steps” => the effects of the four steps on the results ?
Table 1: Explain the last column so that the table can be independently understood.
Figure 2: its caption is confusing with the caption of Figure 2. Do they really have the same caption? At least the lines are quite different. Pls check.
Figure 3: ‘appeared’ in the caption is not exact. What do you mean by this? Is this figure a ‘direct’ treatment of FAO data, or it is after your interpretation detailed in section 2.3.3?
Line 268: “The qualitative results from the three alternatives were as expected if run to equilibrium” => this sentence needs to be expanded to enhance clarity.
Line 276: higher compared with what?
Line 268-276: the discussions here needs improving in two aspects: (1) what are the expected carbon densities for the three interpretations ? This information is already needed in section 2.3.3. Without this we don’t know what are the expected comparisons among the three interpretations of FCO. (2) based on point 1, what is the expected ranking? This is unclear. Hence it is unclear what has been compared with when stating “expected ranking held” in line 274.
Line 280-284: how is the equilibrium determined? How long these emissions can last? The whole point is about extended emissions when moving into equilibrium but the paragraphs ends on uncertainty, which is confusing for me.
Table 2: again, explain the last column.
Section 3.5: a better more descriptive section title is needed.
Figure 6: stacked area figure is not appropriate when there are negative values. Confusing. I would just use multiple panels for different regions. A least it is clearer. Maybe think to combine figure 6 and figure 7 using simple line plot rather than stacked area.
Line 330: this justifies my suggestion to merge Fig 6 and 7.
Section 3.5.2: a more descriptive title could be considered. Of course the whole paper is on emissions by land use.
Table 5: I don’t understand why there is no gross sink in wood products. Not all wood products lead to immediate emissions so there will be some cumulative carbon increase shown as wood product pool compared with a world without any wood harvest. This should be counted as a gross sink, no?
Figure 9. The legends are confusing. The readers have to guess the meaning. I suppose ‘Pasture’ and ‘Cropland’ should represent deforestation or more specifically, forest conversion to cropland, and forest conversion to pasture. But then what is ‘fire’? Should we use ‘afforestation’ or ‘plantation’? I guess ‘plantation’ means there is a net transition in land from agricultural land to forest, but the reason could naturally abandoned cropland. ‘afforestation’ would be a better name. Here there is no ‘forest degradation’ which I also have some comments there. If ‘forest degradation’ cannot be mapped to one of this usages which are relatively clear, are there good reasons we must use this term? For me the land use types shown here are much less ambiguous.
Line 409: I think BLUE and OSCAR are based on LUH? Because in HYDE there are changes in areas of cropland and grazing land but BLUE and OSCAR need land transitions and these were only available in LUH data.
Line 423-424: I get confused. Should Feng et al. be compared with net emissions here or gross emissions ? I would argue for net emissions. I suggest the authors clarify on this first before making such comparison.
Line 465-467: all reported changes by FAO are counted as anthropogenic is a key assumption of this paper and should be stated at the early beginning. My second question is, is this assumption valid and why? This question is also relevant to the whole paragraph of 489-497.
Section 4.2.2 what does the term ‘degradation’ mean here? Is it wood harvest? Selective logging? Or unknown reason for forest loss or decrease in forest biomass? Is this what is called ‘degraded land’ in section 2.3.3? are authors in line 579-585 talking about the same thing by using ‘degradation’?
Richard A. Houghton and Andrea Castanho
Data sets
Annual emissions of carbon from land use, land-use change, and forestry Houghton, Richard; Castanho, Andrea https://dataverse.harvard.edu/privateurl.xhtml?token=09ee9f75-3b93-4755-8be6-9da7ac06dd60
Richard A. Houghton and Andrea Castanho
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