Over-reliance on land for carbon dioxide removal in net-zero climate pledges

Domain: earth_science
Published: 2024-10-23
Editorial outcome: major_revision

Abstract
Achieving net-zero climate targets requires some level of carbon dioxide removal. Current assessments focus on tonnes of CO2 removed, without specifying what form these removals will take. Here, we show that countries’ climate pledges require approximately 1 (0.9–1.1) billion ha of land for removals. For over 40% of this area, the pledges envisage the conversion of existing land uses to forests, while the remaining area restores existing ecosystems and land uses. We analyse how this demand for land is distributed geographically and over time. The results are concerning, both in terms of the aggregate area of land, but also the rate and extent of land use change. Our findings demonstrate a gap between governments’ expected reliance on land and the role that land can realistically play in climate mitigation. This adds another layer to the observed shortcomings of national climate pledges and indicates a need for more transparency around the role of land in national climate mitigation plans.

Introduction
Achieving global net zero carbon dioxide (CO2) emissions is necessary to halt warming on multidecadal timescales1. Some level of carbon dioxide removal (CDR) will be required to balance residual emissions at the point of net zero, though both the scale of CDR and the amount of residual emissions remain contested2. Multiple studies now assess the current and pledged level of CDR in government and corporate climate pledges for net zero3–5. Yet these assessments focus on quantifying removals in terms of tonnes of CO2, which leaves open the question of what form these removals will take. Currently, CDR is generated almost exclusively through land-based measures, and an important question is what land requirements follow from this approach and how this might conflict with other land uses.

The Paris Agreement’s goal of achieving a balance between anthropogenic emissions by sources and removals by sinks of greenhouse gasses in the second half of this century6 has put a spotlight on the role of forests and land in climate mitigation, given the potential to enhance sequestration of atmospheric carbon. Land is central to addressing the accelerating and entwined crises of climate change and biodiversity loss, yet the many and often competing demands made on land are resulting in increasing pressures7. Land-use change is currently the leading driver of biodiversity loss, as well as contributing to climate change, which in turn is expected to drive further biodiversity loss8. CDR efforts through land-based approaches, such as large-scale afforestation and bioenergy carbon capture and storage (BECCS) could reduce future biodiversity losses indirectly, by contributing to climate mitigation9. Such initiatives may also exacerbate the biodiversity crisis due to additional demand for land and other resources10–12, with negative impacts on biodiversity concentrated in regions with high land-use change13. Land-based CDR can also risk undermining the livelihoods of Indigenous Peoples and other vulnerable and land-dependent communities by dispossessing them of access to land-based resources14,15.

The centrality of land to CDR options in both modelled scenarios and current policies gives rise to growing uncertainties about the potential aggregate demand for land to address climate mitigation16. Under the Paris Agreement, countries make climate mitigation, adaptation and finance pledges in the form of Nationally Determined Contributions (NDCs) every five years. Countries have also agreed to submit Long Term and Low Emissions Development Strategies (LT-LEDS) containing mid-century climate pledges, which are increasingly framed as net zero goals. Recent assessments have found both the NDCs and 2050 pledges to be broadly inadequate in meeting the goals of the Paris Agreement17–19. Adding to these concerns over the level of ambition in national mitigation pledges, assessments show many countries plan to rely on substantial levels of CDR, including enhanced land carbon sinks20,21.

While these pledges do not directly translate to national policy priorities and can be interpreted more as aspirational targets, they still give a reasonable indication of the long-term strategies that countries envision. Moreover, even a discursive reliance on CDR can have political implications in the present, by triggering what some have termed a ‘spiral of delay’ where vague statements of future ambition displace near-term mitigation commitments22. This underscores the importance of examining the extent of land implied in the envisaged removals. This matters both to the transparency and integrity of the climate pledges in isolation, but also to their potential impacts on other societal priorities, such as food production and biodiversity protection.

In this study, we assess the expected reliance on land in the mitigation component of national pledges, by reviewing all LT-LEDS or NDCs submitted to the UNFCCC up until the end of 2023 (see methods for more information), building on previous work in the Land Gap report23. Our analysis provides insights into the types of land activities that are envisioned for climate mitigation, and how these are distributed geographically and over time. While the information given by countries in their climate pledges is of insufficient detail to provide accurate assessments of the amount of land that would be required for CDR, and the pledges themselves cannot be taken as precise descriptions of what will happen in the future, our analysis provides an initial estimate of the implications for global land pressure of national climate pledges. More transparency and consistency in country pledges would facilitate future analysis and is necessary to help answer one of the core CDR governance questions posed by the IPCC, namely: which CDR methods governments want to see deployed by whom, by when, at which volumes and in which ways24.

Results
We find that 990 (892–1087) million ha of land would be required to meet the aggregate CDR commitments in country climate pledges from 2020 to 2060. This area is in addition to land already counted towards climate targets, as we included only future land-based CDR in pledges. The aggregate land area is larger than the United States of America, at 983 million ha, or equivalent to two-thirds of the global cropland area, at 1561 million ha in 202025. Of these, 435 (395–475) million ha would entail the conversion of existing land uses to forests or energy crops, while 555 (466–644) million ha would entail the restoration of degraded ecosystems, according to our categorisation of activities (Fig. 1).

National climate pledges
National climate pledges express commitments in a range of different metrics and qualitative ambitions. Of the 194 countries reviewed, it was possible to quantify the land sector mitigation commitments for 140 countries (including EU Member States, which were assessed as a bloc). Pledged activities included land and forest restoration, tree-planting or reforestation, and (for just a few countries) BECCS or direct air capture and storage (DACS). We used three methods to estimate land area in climate mitigation pledges. When carbon removal commitments were not directly expressed as a land area (direct area pledges), we calculated the land area by converting pledges made in tonnes of CO2 removed to land area via IPCC removal factors (emissions pledges). For pledges made as number of trees planted or percentage of forest cover expansion we used external data sources to estimate land area (indirect pledges) (see methods).

Twenty-four countries referred to land management activities resulting in carbon removal in their climate plans, but did not provide any information that was quantifiable. These include large forested countries such as Argentina, Central African Republic, Gabon and Peru. A further 27 countries made no reference to land activities for mitigation, including small island developing states such as Micronesia and Narau; arid countries such as Iraq and Kuwait; and very small states such as Monaco. Countries with large forest area that did not refer to land-based removals in their climate plans include Azerbaijan, Malaysia, the Philippines, and Serbia. In all, this amounts to 51 countries for which we could not quantify CDR (a further 3 countries have not submitted an NDC).

Types of CDR in pledges
Country pledges contain a variety of descriptions of land management activities that we categorised according to IPCC land activity categories (see Table 1).

Table 2 provides an overview of how the land area is distributed across different types of CDR found in pledges. A key distinction is between those activities that propose reforestation or tree-planting that requires a change of land use, and those that restore existing land uses. This distinction is important because activities that involve changes to existing land uses are more likely to infringe on other societal concerns, such as food security and biodiversity protection. Regrowth of managed forests, including replanting after harvest, does not constitute a land-use change according to IPCC guidelines26, and so any reference to a changed management in existing forests was classified as anthropogenic restoration. Forest expansion, new forests or plantations were assumed to involve land-use change if existing forest was not mentioned. We have included energy crops in the land-use change category, although whether bioenergy crops will drive an expansion of agricultural land is dependent on technological advancements such as yield increase, strong land governance and dietary changes27,28. Based on these classifications, more than 40% of the total pledged land area is devoted to reforestation, plantations or energy crops. The rest of the area is pledged for the restoration of degraded forests, agricultural lands, or coastal ecosystems.

Of the land-use change area, 61 million ha would be required for BECCS, with quantified values available for just five countries. While biomass feedstocks range from forestry and crop residues, to biogenic waste29, to dedicated first and second generation energy crops30, none of the countries pledging to use BECCS provide details on how the biomass would be sourced. Bioenergy capture rates vary based on choice of feedstock, yield rates and conversion efficiencies. In the absence of information provided by countries, we have assumed BECCS pledges are met via energy crops using country-specific yield values30 and a 60% conversion efficiency rate following Vaughan et al.31. Different assumptions could reduce or increase the land area required for BECCS, particularly technological advancements and dietary shifts27.

We did not separately assess land area for bioenergy demand (i.e., bioenergy included in energy sector pledges without BECCS), as the focus is on CDR. We also did not quantify pledges for the protection of existing forests that would result in emission reductions. Neither did we include removals from primary forests (occasionally quantified in pledges) as these are non-anthropogenic removals included in the terrestrial land sink32. This is not to underplay the importance of maintaining intact ecosystems and their critical role in climate stabilisation33, but reflects our objective to assess the land area required for additional carbon sequestration specifically.

Restoration commitments have elsewhere been quantified at 1 billion ha based on direct area pledges for 115 countries under the United Nations Convention to Combat Desertification (UNCCD), the Convention for Biodiversity (CBD), UNFCCC and Bonn Challenge34. These restoration pledges only partially overlap with the land area we have quantified in climate pledges, which rely on both direct area pledges (often included in climate commitments and restoration pledges) and emissions-based pledges (only included in climate commitments). Not all restoration pledges made by countries have been included in the climate mitigation pledges we assessed. If climate and restoration pledges were taken together, the area would likely be larger than our total of 1 billion hectares. This speaks to the uncertainty of presenting land pledges without spatial analysis, and to the lack of coordination between different environmental conventions, which exacerbates the difficulty of assessing trade-offs and conflicts between different societal objectives.

Temporal distribution of land in climate pledges
Looking at the temporal distribution of pledges shows that countries rely on an additional 211 million ha of land for carbon removals by 2030, which scales up to a total of 990 million hectares by 2060 (Fig. 2). Net-zero pledges for 2050 and 2060 include larger areas of land, meaning the reliance on land in mitigation pledges can be expected to increase as more countries make net-zero pledges. This resonates with recent analysis which shows that CDR is expected to play a larger role in mitigation pledges towards and beyond 20504.

Our results indicate a remarkable rate of land use change of up to 13 million ha per annum if the reforestation component of pledges is assumed to scale up linearly from 2020 until 2050 (with only 50 mha of reforestation to take place after 2050). Comparing these country intentions to past peaks in land appropriation may be indicative of the risks involved. For example, over the period 2007–14, which was the most intensive period of what has been dubbed ‘the global land rush’, an average of seven million ha was transacted per year in the Global South. This development was seen as a great threat to small scale farmers’ land tenure security and livelihoods35. Monitoring of large-scale land transactions show that by 2020 between 30 and 73% of this area has been converted to agricultural production, with far-reaching consequences for rural livelihoods and natural habitats36.

Future scenarios provide another point of comparison. Modelled pathways that limit warming to 1.5°C with no or limited overshoot show increases in forest cover for carbon removal of 322 million ha (median, with a range of −67 to 890 million ha)16. Many of these pathways also include large amounts of energy cropland area, to supply biomass for bioenergy and BECCS, with 199 (median, 56–482 range) million ha by 205016. While these scenario ranges do not reflect a statistical sample37, it is illustrative that delivering the median scale of CDR projected in these pathways would require an average land-use change of 17 million ha per year between 2020 and 2050.

Hence, our analysis suggests that the rate of direct land use change for carbon removal included in national climate pledges, at 13 million ha per year, is unprecedented from an historical perspective. Furthermore, it is comparable to the average rates of land transformation assumed in global modelled scenarios by mid-century that have raised concerns within the scientific community exactly over their vast consequences for land use, governance, and rural livelihoods38,39.

Geographical distribution of land in climate pledges
A few countries have pledged a large proportion of the aggregate land area. Just four countries (Russia, Saudi Arabia, the US, and Canada) contribute over 70% of the global total and the ten largest countries amount to 85% (Fig. 3). These are all large countries and all major fossil fuel producers. Of the 10 largest country pledges, only Saudi Arabia and Australia explicitly mention that they intend to use internationally traded credits or tree planting in other countries to help meet their pledges.

Russia has the largest CDR area, based on a pledge to more than double the absorptive capacity of managed ecosystems40, which we calculate as 350 million ha of forest regrowth or 21% of Russia’s total land area. Around ten percent of this could potentially be achieved by regrowing abandoned cropland41. As part of its plan to reach net zero by 2060, Saudi Arabia has pledged to plant approximately 40 billion trees in neighbouring countries, equivalent to 200 million ha42. This is part of the Saudi hosted Middle East Green Initiative, which includes a strong focus on tree-planting43. The large land area pledge of the US is explained by a modelled reliance on reforestation and technological CDR of 1000–1800 Mt CO2 per year by 205044. The strategy is not spatially explicit, but we estimate 54 million ha would be required for reforestation and a further 54 million ha for BECCS to deliver the upper end of expected CDR.

Other countries with the 10 largest land area pledges for CDR are shown in Fig. 3. India has promised to create an additional carbon sink of 2.5–3 billion tonnes of CO2 through reforestation by the year 2030, requiring additional forest area of 24 million ha, or 8% of India’s land area. India’s national policies to increase tree cover have already been criticised for failing to consider questions of land ownership, existing land use patterns, and ecological factors such as suitable tree species and elevation45. Australia’s land area pledge is inflated by a large reliance on BECCS to meet its 2050 targets, despite no policy discussion to date on this approach, and includes internationally traded forest carbon credits46. China pledges to increase forest coverage to 25% by 2030, requiring an expansion in forest cover of some 19 million ha from 202047. This is part of a decades-long effort from China to combat land degradation and desertification, and now climate change, with tree-planting48,49. On the restoration side, we counted a large area of forest restoration in the EU, based on the 2023 LULUCF Regulation50, which for the first time includes biological land removals in the EU climate target. Brazil and Ethiopia have pledged large areas of land for restoring degraded forests and pasturelands, with smaller areas of forest expansion.

When calculating the share of national land area devoted to CDR, many low-income nations stand out, particularly in Africa. Figure 4 shows the 16 countries with the largest share of their land area pledged for CDR. Only five of these countries do not fall into the category of least developed countries (LDCs) or most vulnerable countries (including Africa). This could substantiate fears of an impending land rush36 and resulting dispossession of rural communities as these poorer countries plan to devote substantial parts of their national land area to CDR efforts. Conversely, given that more than half of emissions from many low income countries originate from land-use and are bound to development and food security imperatives, we can expect a greater focus on the land sector in these countries’ climate plans. Most of the pledges from LDCs focus on agricultural regeneration rather than reforestation or tree-planting-activities that can take place over large areas in agriculturally dependent countries without displacing people or food production. The two countries that have pledged more than 100% of their land area in NDC targets (Dominica and Equatorial Guinea) are explained by a combination of direct area and emissions-based pledges being made, where the governments may not have considered, or may use different methods to arrive at, the land area required for emissions-based CDR pledges.

Methods
Sample
Climate pledges were reviewed for 194 countries. The European Union and its 27 Member States communicated one joint NDC, hence we have analysed the climate pledges of the EU as a bloc, rather than individual Member States. Three countries have not submitted an NDC, meaning that pledges for 164 countries plus the EU were assessed. To assess the reliance on land in these national pledges, we reviewed all LT-LEDS or NDCs submitted to the UNFCCC up until the end of 2023 (with the exception of Brazil for which we assessed the 2015 NDC following government announcements to reinstate that NDC63). We focused on LT-LEDS as a proxy for net zero and 2050 targets. That is, we assessed the longest-term pledge that was available, assuming that any land-based CDR in near-term pledges is encompassed in longer-term pledges. For countries without long-term pledges, we reviewed NDCs. For a handful of countries that had not included CDR in their UN submitted climate pledges we included other government statements.

CDR typology
Country climate strategies and pledges express commitments in a range of different metrics and qualitative ambitions. Therefore, a number of assumptions were made to identify the scale of CDR commitments, and the associated land area required. CDR was presented in climate pledges as a range of different land management activities, or technology or emission based commitments, including: emissions reductions required to achieve net zero or interim (2030) targets compared with total emissions (presented in Mt CO2e or percent of total emissions); references to residual or remaining emissions at the time of net zero; references to removals/sequestration/CDR (presented in Mt CO2e or proportion of total emissions); direct reference to land area (in hectares, acres or km2) or proportion of land area (of country, or of a land cover type, i.e.: proportion of forest cover to be maintained or extended, and as number of trees to be planted). We categorised these pledges into three types: direct land-area pledge, indirect land-area, or emissions-based. Direct area is reported directly from the pledge, while indirect and emissions-based pledges are converted into land area through the methods described below.

The various approaches to land management activity types in national climate strategies were categorised into seven activity types, based on their carbon sequestration potential (using IPCC removal factors). Table 1 shows the seven land-use categories used, in relation to ecosystem condition, with country examples that highlight the key search terms used. ‘Primary forests’ are intact natural forests with minimal disturbance (key terms – primary, protected). ‘Old secondary forests’ were selected to represent regeneration of degraded natural forests (key terms - restoration, forest management, forestry). ‘Young secondary forests’ refers to establishing new forests of mixed species (key terms - reforestation, forest expansion). ‘Plantations’ was used when countries referred to establishing commercial forests or monoculture forests (key terms – afforestation, plantations) ‘Bioenergy’ was used when countries referred to BECCS deployment (key terms - BECCS). Agricultural landscapes were classified into two broad categories – ‘Agroforestry’, for pledges that referred to agricultural regeneration or integrating trees into agricultural landscapes (key terms – regeneration, agroforestry, mixed uses), and ‘Silvopasture’, for pledges that referred to restoring degraded rangelands (key terms – rangelands, silvopasture). The activity type ‘Mangroves’ was used to quantify the removal potential of restoring or expanding mangroves.

This categorisation represents a simplification of the range of land management activities and practices that countries have referenced in their climate strategies, and which result in CDR.

Table 2 characterises these seven land management categories based on whether the primary intervention involves protection, restoration or replanting, and shows the land area for each activity type. Pledges for avoided emissions and the protection of existing forests were noted, but not quantified in the context of our aim to assess the land area required for carbon dioxide removal in national climate pledges. For agricultural activities, removal factors were sourced from the IPCC64. For forestry activities, removal factors were sourced from ref. 65 For bioenergy, country specific median yield values were sourced from ref. 30, and a conversion efficiency of 60% was assumed following ref. 31. Subjective choices around conversion efficiency, which varies from 40% to 90% across studies, can impact the results in terms of land area required, and hence the perceived feasibility space (See Table S1 for details of calculations used). It should be noted that climate effects on energy crop yields are not captured by Li et al.30, and have already been observed to reduce agricultural productivity62. Similarly, climate change effects, such as CO2 fertilisation on forests are not captured by Harris et al65. With future changes in climate, carbon storage capacity may change over time, increasing through factors like CO2 fertilisation, which may weaken over the century as climate effects start to take over from CO2 fertilisation and other effects66. These indirect, climate and CO2 feedbacks are uncertain and remain model-dependent67–69.

Converting emissions based and indirect pledges to land area
For emissions-based pledges, default removal factors from the IPCC were applied based on the activity type and climate domain of the country (or implementation area, if this was identified as being outside the pledging country) for the CDR typology derived as described above. A more accurate representation of the variety of land management activities would entail considerably more work, but would not greatly change the results, given that the range of emissions removal factors that can be applied is limited. A sensitivity analysis using a global average removal factor resulted in an 8.4% increase in land area (117 million ha) showing that the use of biome and activity specific removal factors constrains the calculation of land area, but selection of activity types does not determine the results. Removal factors are based on above ground biomass only. Including a below-ground biomass increment for relevant activity types decreases total land area by 8.9 million ha, which is less than 1% of the total land area (See Supplementary Data70 and Table S3).

For indirect pledges made as a proportion of forest cover or land area, we used data from publicly available datasets on land cover and land use from the Food and Agriculture Organization of the United Nations (FAO), and national GHG emissions profiles such as the Climate Analysis Indicators Tool, to calculate the implied land area when not directly stated. For indirect pledges made as number of trees planted, tree density per hectare was taken from Crowther et al.71, depending on the ecoregion of the country in question (See Table S2).

Uncertainty analysis
We estimated uncertainty in the land area estimates from emissions-based pledges and indirect area pledges at the scale of climate domain and activity type because the estimates were computed from uncertain values. We followed a propagation of uncertainty approach, which reflects calculations of variances (and hence, s.d.). We note that the uncertainty analysis, being based only on the denominator to calculate land area, will be an underestimate. Many other variables contribute to uncertainty in the aggregated data, including biome classifications and assumptions made in interpreting country statements.

For emissions-based pledges, uncertainty estimates were based on uncertainties in the removal factors from ref. 65 for forest land, IPCC64 for agricultural land, and ref. 30 for bioenergy. For indirect pledges, uncertainty estimates were based either on tree-density s.d. from ref. 71 or where total forest or land area reported to the FAO25 was used, no uncertainty estimates are available. For direct area pledges, we assumed the uncertainty to be zero. Table S1 shows the source and contribution of the relevant denominator, along with its associated uncertainty. Mean and s.d. values shown in figures are based on an aggregate of the relevant data rows in the Supplementary Dataset70.

The land required s.d. was computed using a standard formula depending on which method was used to compute the land required, assuming that the mean of the tree density or removal factor is sufficiently larger than zero.

land required = (treedensitySD / treedensity)
or
land required = (removalfactorSD / removalfactor)

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Review of “Over-reliance on land for carbon dioxide removal in national climate pledges” by Kate Dooley, Kirstine Lund Christiansen, Jens Friis Lund, Wim Carton\nNature Communications\nRecommendation: Revise and resubmit\nKey results\nThe authors reviewed country pledges that express climate commitments related to land and that are represented as a range of different metrics and qualitative ambitions. Several countries (53 of ~165, or ~32%) did not provide enough information for the authors to include in their assessment. This compilation exercise by the authors is in itself commendable, as the information provided by countries tends to lack transparency, making it difficult to synthesize the information as was done in this paper. The authors’ recommendation in the conclusion is well supported that greater transparency is needed around the approach to land management in climate mitigation plans and the assumptions made more clear about the land area needed for their land-based mitigation commitments.\nFrom their review, the authors conclude that based on current pledges, approximately 1.1 billion ha of land would be needed globally for land-based CO2 removals to be delivered as pledged by countries over the time period 2020-2060, an area equivalent to two-thirds of global cropland area. From this analysis, the authors suggest that these commitments place too much expectation on land to deliver on the Paris goal of achieving a net balance between anthropogenic emissions by sources and removals by sinks of GHGs in the second half of the century, potentially undermining the need for near-term emission reductions.\nValidity and robustness of conclusions\n• The type of analysis as conducted in this paper is helpful, but mainly as an example of how the analysis the authors WANT to conduct in a credible manner is simply not possible based on the information provided. I would like to see it re-written with this angle, rather than trying to pass off the analysis that was done as something analytically robust. As currently written, it is more appropriate for a specialized policy audience as a back-of-the-envelope estimate for those following UNFCCC negotiations. As currently formulated, the estimates lack the analytical rigor I would expect from a high-profile Nature publication and the findings do not represent a particularly significant or novel advance to specialists in the field. This is less the fault of the authors and more the fault of the bad data they had to work with.\n• The main push of the paper is to voice concern over the amount of land required to remove carbon dioxide at the scale and pace countries have pledged as a way to get us out of this global climate mess. To put this in context, it could be helpful if the authors mention country pledges on the emission reductions side as well, not just for land but overall across sectors; are these equally concerning or is the concern limited just to CDR on land? Are emission reduction pledges more realistic than the land CDR pledges or similarly unrealistic? Might be worth making a point up front that these commitments/pledges may be set by countries to be overly ambitious on purpose, to be used more as aspirational targets/tools for political posturing than as having any basis in reality. The example of corporate commitments made in 2014ish to end deforestation by 2020 comes to mind: was that goal achieved? No. Was it a useful pledge to rally around a collective vision of hope? Yes. Once that narrative is set up about what role these pledges play, and how the Paris Agreement encourages ratcheting up of ambition over time, then the authors could make the recommendation/conclusion backed by their analysis that pledges should be more realistic and transparent about the additional climate mitigation that CDR from the land sector could actually provide.\n• The authors acknowledge that their analysis required many assumptions to arrive at their estimates. Based on my review of the online methods and the excel spreadsheet, these assumptions are not as clearly outlined as I hoped they would be for a reviewer with limited time. More straightforward explanation would be helpful about how the land area estimates per country were calculated and more explanation provided in what assumptions were used where. The authors should clearly acknowledge the limitations of their analysis and that the result from their uncertainty analysis is surely an underestimate.\nData and methodology\n• The authors’ division of land into reforestation involving a change in land use vs. restoration of degraded forests is somewhat puzzling to me. The authors imply that reforestation involves a land-use change, but depending on country context reforestation may be synonymous with restoration of forest land remaining forest land. For example, are trees growing back after harvest – as may be prevalent in three of the four countries identified that contribute substantially to the global total land area for CDR (Russia, US and Canada) - counted by these countries as reforestation or restoration of a degraded forest? Regrowth of young secondary forests and plantations may not result in a change of land use because it may be considered by countries as forest land remaining forest land.\n• It was difficult for me to follow the specifics of what was happening in the cells of the Land Gap Calculator spreadsheet. It would be helpful to include more information in the Notes tab, and/or provide further explanation in the supplementary Word doc, of a worked example of how estimates are derived for different scenarios when carbon removal commitments were not expressed directly as land areas. For example for each of the pledge types, provide an illustrative example of how the authors translated it into an estimate of land area. Saudi Arabia was based on a pledge on number of trees – the conclusions of the paper depend heavily on how that number of trees estimate was translated into an area of land and what assumptions were used. Currently all that is hiding in spreadsheets and supplementary material, but it’s critical to elevate the assumptions used to the main text if the paper’s conclusions are to be supported.\n• Similarly, Russia’s importance to the overall geographic distribution of land in climate pledges (33% of the total) would be particularly important to understand how the estimate was derived, since it was not a direct pledge of land area. How does a pledge to “more than double the absorptive capacity of managed ecosystems” translate into the assumptions made by the authors to arrive at the land area needed? These country pledges may be designed to be vague on purpose, and that point could be made in the paper.\nAnalytical approach\n• I suggest the authors review national GHG inventories to understand what level of CO2 removals are reported by countries, to put the CDR pledges into context.\n• It is not clear to me how the mean and standard deviation of areas of restoration and reforestation were calculated in Figure 1.\n• The authors didn’t assess bioenergy demand or quantify pledges for protection of existing forests that would result in emission reductions, or include CO2 removals from primary forests as these are non-anthropogenic removals included in the terrestrial land sink. Focus is on additional C sequestration specifically. More clarification should be provided on how countries account for current CO2 removals in secondary forest and plantations, vs. additional CO2 removals from “restoration” or “reforestation” of secondary forest. See also Nabuurs et al. 2023 (Communications Earth and Environment) who argue that carbon dioxide fluxes from all forest land (managed and unmanaged) need to be recorded by countries in order to help track progress towards global climate targets.\n• Uncertainty analysis: Note that removal factors and their uncertainties from IPCC 2019 refinement for temperate forests were revised in a correction published by IPCC in July 2023.\n• This may be beyond the scope of the paper, but some reference could be made to the biophysical processes that may enhance or diminish the climate effects of carbon released or absorbed from forest biomass (e.g. albedo), particularly if a substantial portion of land-based CDR is expected to come from temperate and boreal regions (Russia, Canada, USA).\nSuggested improvements\n• Use active voice (We provide a first estimate” vs. “this paper provides a first estimate”)\n• Per Nature guidelines (I think), avoid claims of novelty (“it provides the first assessment of its kind”)\n• Abstract and throughout: avoid vague statements like “implying impacts on people and food security”. What kind of impacts?\n• Include in the introduction more context for the general reader of what the Paris Agreement goal is – achieve a net balance between anthropogenic emissions by sources and removals by sinks in the second half of the century. Important to include anthropogenic and to stress the role of forests on the sinks side.\n• Perhaps worth pointing out that the idea that all countries achieving net-zero within their own boundaries doesn’t necessarily make sense because all countries have a different starting point when it comes to carbon dioxide removals on land. Some developing countries are already net zero/net sinks! So it’s an important point to make that to increase CO2 removals beyond those that exist in the country now, we need to assess the level of ambition in climate pledges and what CDR would be on top of current CDR in the land sector.\n• Another point to highlight might be how land use history is likely to play a role in how CDR actually plays out – how much CDR an ecosystem can support may differ from the CDR that countries are pledging to deliver. The way that these policies play out and how land is actually used will depend upon local land tenure as well as other social and economic factors.\nClarity/context\n• “We present a breakdown of what these removals would look like” – this is too vague, suggest deleting from abstract. More clear: “We present a breakdown of how demands for land would be distributed geographically and over time”\n• “For more than half of this area, the pledges envisage the conversion of existing land-uses to forests, while the remaining area is for restoration of degraded ecosystems.” What is a “degraded ecosystem” as defined by various countries? How much overlap is there between existing land uses (several of which are degraded from their natural state) and degraded ecosystems? Not clear how this breakdown was determined after reading through the methods.\n• Not clear how land for reforestation/plantations for BECCS is calculated\n• Introduction: “many climate mitigation approaches that rely on land, such as large-scale afforestation, threaten to exacerbate rather than address the biodiversity crisis.” Change to “some” approaches, as many climate mitigation approaches that rely on land have positive biodiversity benefits if implemented well.", "reviewer_2": "The paper, entitled \"Over-reliance on Land for Carbon Dioxide Removal in National Climate Pledges\", makes a significant and relevant contribution to the climate policy literature, focusing on the assessment of land requirements for land-based mitigation options and the associated risks. As a publication based on the analysis of the \"Land Gap Report\", it provides a timely contribution to the scientific literature, esp. in the context of next NDCs due in 2025. However, there are several issues that require attention and major revisions before publication.\n1.Relevance of the documents for domestic climate policy making:\na. There is a flurry of analyses of NDCs and LT-LEDS. What is usually missing is a reflection on the political role of these documents. The lack of submitted LT-LEDS, for example, indicates the low political priority that UNFCCC signatories attach to these reporting mechanisms. It should be emphasised that not only is the implementation gap between actual policy and NDC/LT-LEDS huge, but also that these strategy documents have limited relevance for national climate policies and that these political contexts for specific pledges cannot be identified from these documents. This is not to say that a quantitative analysis of the documents should not be done, but the framing of such an analysis should take into account this limitation arising from the data source of strategy documents that may not fully reflect a country's policy priorities.\nb. The paper should provide additional interpretation and policy contextualisation, particularly regarding the high numbers from individual countries, such as Russia. This will help to interpret the high headline number reported at the beginning of the paper.\n2.Methodology:\na. The methodology used to extract data from the documents should be clarified. At present, the supplementary material lists the sources of the documents and calculations but not the exact wording on which the calculations are based. This makes it difficult to trace the commitments and check for consistency and accuracy.\nb. The paper currently categorises all types of land restoration as mitigation/CDR commitments. Given that land has been managed for a long time and that objectives have changed (e.g. combating desertification, biodiversity,...), it might be worth reflecting that CDR may not be the primary objective of all the pledges collected here, but could also be a side-effect/co-benefit of an initiative that policy makers had in mind for other reasons - it may not be all about CDR. It would be useful to distinguish between pledges that are explicitly focused on carbon removal and those where CDR is a secondary or co-benefit. This clarification will provide a better understanding of the nature and intent of the pledges.\nc. Related to Issue 1: The use of government documents (instead of NDC/LT-LEDS in the analysis should be explained (why are government documents used in some cases?) There are significant gaps between NDCs/LT-LEDS and actual national policy making (see also Issue 1). This should be better explained - or focus on only one type of document. Alternatively, the paper could consider focusing on one type of document to provide a more consistent analysis.\n3. Permanence/reversibility of CDRs:\na) The issue of reversibility and different permanence periods for different types of sequestration is critical, but is not addressed in the pledges and is not explicitly raised in the paper. Given the aim of the paper to inform the review of NDCs, it is important to highlight the challenges associated with relying on LULUCF-based CDR to meet climate goals. The potential measures to incorporate them into CDR policy, such as buffer pools and equivalence discounting, should be raised to highlight that land requirements could be even higher if LULUCF-based CDR is responsibly governed to meet climate goals.\nIn conclusion, the paper makes an important contribution to climate policy by addressing the role of land-based mitigation options in national climate commitments. In order to improve the relevance of the paper, it is recommended that the above issues are addressed in a major revision. By doing so, the paper can provide a more comprehensive and insightful analysis of the issue and have a greater impact on the climate policy discourse.", "reviewer_3": "I noted reading this paper and consider it a very worthwile contribution.\nThe paper evaluates the scale and potential land-use conflicts (and other challenges) for nations to deliver on pledges around LULUFC and BECCCS. I addresses and highlights the uncertainty and risk of presenting these land pledges in the absence of robust local assessment and especially spatial analysis. The same risk applies to national pledges as they pertain to energy efficiency, renewable energy expectations, and CCUS (especially storage). This lack of spatial grannularty obscures a multitude of risks and uncertainties when it comes to resource capacities, environmental considerations and local values.\nIn the case of the land sector, the lack of coordination between different environmental conventions is especially problematic.\nThe paper is timely, as we approach COP28, proposals to update NDCS, and the IAMs modelling updates ahead of the 7th Assessment Report.\nAcknowledging that I am not an expert in land sector analysis, the analytical work done appears robust and uses sound sources. The authors also acknowledge clearly the uncertainties and limitations on the analysis but I agree they have landed at a conservative place.\nThe paper is also very well written. I had a couple of very minor comments:\nOn page 6, where the authors write: \"For example, the global land rush of the 2000s, which was seen as a great threat to small scale farmers, saw no more than seven million ha being transacted per year.\" Authors could perhaps add some descriptive context noting the broad readership of Nature Comms. E.g.:\n\"For example, the global land rush of the 2000s for the purpose of industrial-scale agriculture and resource extraction…, which was seen as a great threat to small scale farmers, saw no more…\"\nAlso suggest the insertion of \"approximatey\" or \"around\" in a number of places, given the acklnowldged uncertainty in parameter. e.g. \"Saudi Arabia has pledged to plant an additional 40 billion trees in neighbouring countries, equivalent to (around) 200 million ha\".\nOtherwise I recommend for publication."}, "author_response": "Response to review – Over-reliance on land for carbon dioxide removal in national climate pledges\n*NB: line numbers referred to below are in the track change version, with deletions in text.\nReviewer #1:\nKey results We thank the reviewer for these remarks\nThe authors reviewed country pledges that\nexpress their climate commitments related to\nland and that are represented as a range of\ndifferent metrics and qualitative ambitions. \nSeveral countries (53 of ~165, or ~32%) did not\nprovide enough information for the authors to\ninclude in their assessment. This compilation\nexercise by the authors is in itself commendable,\nas the information provided by countries tends to\nlack transparency, making it difficult to synthesize\nthe information as was done in this paper. The\nauthors’ recommendation in the conclusion is\nwell supported that greater transparency is\nneeded around the approach to land\nmanagement in climate mitigation plans and the\nassumptions made more clear about the land\narea needed for their land-based mitigation\ncommitments.\nFrom this review, the authors conclude that\nbased on current pledges, approximately 1.1\nbillion ha of land would be needed globally for\nland-based CO2 removals to be delivered as\npledged by countries over the time period 2020-\n2060, an area equivalent to two-thirds of global\ncropland area. From this analysis, the authors\nsuggest that these commitments place too much\nexpectation on land to deliver on the Paris goal of\nachieving a net balance between anthropogenic\nemissions by sources and removals by sinks of\nGHGs in the second half of the century,\npotentially undermining the need for near-term\nemission reductions.\nValidity and robustness of conclusions\nThe type of analysis as conducted in this paper is #1\nhelpful, but mainly as an example of how the type We thank the reviewer for this comment. We have\nof analysis the authors want to conduct in a reframed the abstract, introduction and objectives at\ncredible manner is simply not possible based on the start of the paper in many places to make clearer\nthe information provided. I would like to see it re- that the land found in climate pledges may or may not\nwritten with this angle, rather than trying to pass be implemented. We make two specific points related\noff the analysis that was done as something to this:\nanalytically robust. As currently written, it is more\nappropriate for a specialized policy audience as a - That we assess how much land would be required\nback-of-the-envelope estimate for those following if country pledges were implemented, not how\nUNFCCC negotiations. As currently formulated, much land we expect to see used for CDR in\nthe estimates lack the analytical rigor I would reality. See Page 2, line 45 – page 3, line 3.\nexpect from a high-profile Nature publication and - That the information given by countries in their\nthe findings do not represent a particularly climate pledges is of insufficient detail to provide\nsignificant or novel advance to specialists in the accurate estimate of the amount of land that\nfield. This is less the fault of the authors and more would be required to meet climate mitigation\nthe fault of the bad data they had to work with. pledges. See Page 3, lines 19-26.\nWe also underscore this point in the discussions and\nconclusion where we talk about more transparency\nneeded.\nHowever, we defend the analysis as being analytically\nrobust on the basis of the detail we have gone into\n(where possible) to quantify land area in pledges. This\nshould be clearer in the spreadsheet now that our\ncalculation assumptions have been added (see column\nT). For some countries we have separately assessed up\nto 6 different land sector activities in order to quantify\nthe different carbon uptake potential of different\nactivities (eg: Niger, Uganda, Uruguay). Other countries\nhave clearly stated how much land they intend to use\nfor mitigation (eg: Brazil, Bolivia, Colombia). For\ncountries that have only stated tonnes CO2 removed,\nthere is uncertainty associated with the assumptions of\nactivity types and different removal factors – we have\nfurther emphasised these uncertainties throughout the\npaper and in the online methods.\nIn addition, we have added a sensitivity analysis where\nwe assume global average removal factors for all\nemissions-based pledges (removing any interpretation\nabout the type and location of land-based activities)\nwhich shows an increase of 10% from our results,\ndemonstrating it is not our assumptions regarding\nactivity types or removal factors which significantly\ndrive the results.\nAs the results are an aggregate of a relatively large\ndata-set (194 countries and 296 separate spreadsheet\nquantifications), differences in interpretations of\ncountry intentions where these are unclear do not\nsignificantly change the overall results.\nThe main push of the paper is to voice concern #2\nover the amount of land required to remove We agree with the reviewer that readers should\ncarbon dioxide at the scale and pace countries understand the overall context of pledges, and whether\nhave pledged as a way to get us out of this global pledges on the emissions reductions side are on track\nclimate mess. To put this in context, it could be and have made several edits to accommodate this.\nhelpful if the authors mention country pledges on\nthe emission reductions side as well, not just for We quantify land area to highlight that embedded in\nland but overall across sectors; are these equally the already insufficient national climate pledges are\nconcerning or is the concern limited just to CDR unrealistic claims to land that render them even more\non land? Are emission reduction pledges more insufficient. This is an important point in its own right -\nrealistic than the land CDR pledges or similarly regardless of how one interprets the possible roles of\nunrealistic? Might be worth making a point up pledges. We haveclarified the role of these pledges as\nfront that these commitments/pledges may be government commitments under the Paris Agreement\nset by countries to be overly ambitious on (Page 2, lines 27-43), so they are not comparable to\npurpose, to be used more as aspirational voluntary corporate pledges. We have presented a\ntargets/tools for political posturing than as having great deal of new data in this paper by focusing on land\nany basis in reality. The example of corporate area as a quantification metric, and believe that\ncommitments made in 2014ish to end comparing these land pledges to emissions reductions\ndeforestation by 2020 comes to mind: was that in other sectors on a country by country basis is outside\ngoal achieved? No. Was it a useful pledge to rally the scope of this paper.\naround a collective vision of hope? Yes. Once that\nnarrative is set up about what role these pledges To contextualise the land pledges in comparison to\nplay, and how the Paris Agreement encourages pledges in other sectors, we have:\nratcheting up of ambition over time, then the\nauthors could make the - Made clear the political role that pledges play as\nrecommendation/conclusion backed by their aspirational targets, rather than as precise\nanalysis that pledges should be more realistic and descriptions of what will happen in the future\ntransparent about the additional climate (Page 2, line 45).\nmitigation that CDR from the land sector could - Added a reference to recent assessments from the\nactually provide. UNFCCC and UNEP which conclude that both NDCs\nand LT-LEDS pledges are inadequate, showing that\nemission reduction pledges are not on track to\nmeet the goals of the Paris Agreement (See Page 2,\nlines 31-32).\n- Added a discussion on estimates that considering\n2050 pledges could put us on a path to below 2C,\nyet given the majority of large land area pledges\nare in 2050 targets, this calls into question\nwhether these long-term pledges can be\nimplemented (Page 11, line 15-18).\n- Made clear that the level of detail in pledges does\nnot allow for accurate assessments of land area\n(Page 3, lines 19-24).\nWe agree with the reviewer that it is important to set\nup a narrative about the role that pledges play and the\nneed to ratchet ambition over time. This is spelt out in\nour conclusion section where we call for “scaling up\nambition levels in near-term emissions reductions\nrather than striving to achieve what appear to be\nunrealistic targets for land-based CDR.”\nThe authors acknowledge that their analysis #3\nrequired many assumptions to arrive at their We have implemented several changes to clarify the\nestimates. Based on my review of the online assumptions we made in quantifying land area from\nmethods and the excel spreadsheet, these pledges and to acknowledge the limitations of the\nassumptions are not as clearly outlined as I hoped analysis. These are:\nthey would be for a reviewer with limited time.\nMore straightforward explanation would be - Clarified the three methodological approaches we\nhelpful about how the land area estimates per used to calculate land area (direct area, indirect\ncountry were calculated and more explanation area, emissions based) where this is first\nprovided in what assumptions were used where. mentioned in the manuscript (Page 4, lines 2-8).\nThe authors should clearly acknowledge the These approaches are also referenced in the label\nlimitations of their analysis and that the result to Fig 1, and explained in full in the online methods\nfrom their uncertainty analysis is surely an and repeated in the SI, but we agree it is also\nunderestimate. important to make the quantification approaches\nclear where readers first encounter this.\n- We have rephrased the discussion section where\nwe explain why our analysis is likely to be an\nunderestimate as a limitations section, to make\nclearer the limitations of our study, including not\nassessing bioenergy (see response #9, below)\n(Page 10, line 23 – page 11, line 7).\n- We note that the calculated uncertainty values are\nan underestimate as they are only based on\nremoval factors, when there are many other areas\nof uncertainty in the data (in online methods, page\n14, lines 20-23).\n- We have added notes for each calculation row into\nthe spreadsheet to explain the assumptions\nbehind interpreting each land activity from country\npledges (see column T).\nWe have added more information to the Notes page of\nthe spreadsheet to explain which spreadsheet columns\nkey information is found (land area results, calculation\nnotes) and also to explain again the direct, indirect or\nemissions based methodological approach and where\nin the spreadsheet this information can be found.\nData and methodology\nThe authors’ division of land into reforestation #4\ninvolving a change in land use vs. restoration of Our assumptions regarding reforestation = land use\ndegraded forests is somewhat puzzling to me. The change and restoration of degraded forests does not\nauthors imply that reforestation involves a land- equal land use change are based on IPCC LULUCF\nuse change, but depending on country context accounting guidelines. Hence, if an NDC or long-term\nreforestation may be synonymous with pledge indicated trees growing back after a harvest\nrestoration of forest land remaining forest land. (such as improved forest management), we would\nFor example, are trees growing back after harvest interpret this as forest land remaining forest land, in\n– as may be prevalent in three of the four line with IPCC guidelines, and therefore would\ncountries identified that contribute substantially categorise this as restoration, as the reviewer rightly\nto the global total land area for CDR (Russia, US points out.\nand Canada) - counted by these countries as\nreforestation or restoration of a degraded forest? In most cases, there is very little information in the\nRegrowth of young secondary forests and pledges, but we used key terms to categorise pledges\nplantations may not result in a change of land use into our 7 activity types, which then correspond to\nbecause it may be considered by countries as restoration or land use change (see Table 2, page 6 for\nforest land remaining forest land. CDR typology and terms). To make our search and\nclassification approach clearer, these key terms have\nnow been included in the online methods (page 13),\nand we have highlighted country examples in Table 1\nthat use these key terms. We only categorise activities\nas reforestation if afforestation, reforesting or\nestablishing plantations is specifically mentioned, with\nno reference to forest management or an existing\nforest. We have added a clarification that any reference\nto forest management is considered restoration and\nregrowth of young secondary forests and plantations\nmay be considered by a country as forest land\nremaining forest land, but if the pledge does not\nspecify the reforestation is taking place in an area\ncategorised as forest land, then we will assume it is\nland-use change (See Page 5 line 11- page 6, line 3).\nWe accept that our categorisations are somewhat\narbitrary, but they are designed to give an indicator of\nthe type of land-use activities pledged by countries and\nnot an accurate prediction of what will happen, as\nnoted in comments above.\nIn the country specific cases the reviewer mentions,\nour interpretation of activity and land-use change or\nrestoration should now be clear from the notes we\nhave added to the spreadsheet (column T).\nFor the US, Canada and Russia:\n- the US refers to opportunities for reforestation\nand targets for CDR such as BECCS or DACCs,\nhence we assume all of this would require land use\nchange (we calculate reforestation and BECCS\npotential separately and do not count the sink\ncapacity of existing forests that they reference).\n- Russia refers to ‘managed ecosystems’ hence we\ninterpret that as restoration, not land-use change,\nand they quantify the sequestration potential,\nwhich we convert to land area.\n- Canada refers to increasing its LULUCF sink, so we\nassume that is in managed forests hence\nrestoration. We exclude the current sink in existing\nforests. They also refer to BECCS, which we\ncalculate as land-use change.\nThese assumptions and calculations can now be seen\nfor each country in column T of the spreadsheet.\nIt was difficult for me to follow the specifics of #5\nwhat was happening in the cells of the Land Gap We appreciate this comment from the reviewer, and\nCalculator spreadsheet. It would be helpful to the difficulty of following the specifics in the Land Gap\ninclude more information in the Notes tab, and/or Calculator spreadsheet.\nprovide further explanation in the supplementary\nWord doc, of a worked example of how estimates We have now added in further information in the notes\nare derived for different scenarios when carbon tab of the spreadsheet, as requested. This gives specific\nremoval commitments were not expressed and relatively detailed guidance for how each pledge\ndirectly as land areas. For example for each of the was interpreted and calculations made. Table 1 in the\npledge types, provide an illustrative example of manuscript is designed to provide information on how\nhow the authors translated it into an estimate of the different types of pledges are interpreted as\nland area. Saudi Arabia was based on a pledge on different activities, as explained above at response #4.\nnumber of trees – the conclusions of the paper\ndepend heavily on how that number of trees We note that in the case of Saudi Arabia, this is labelled\nestimate was translated into an area of land and as a ‘direct’ land area pledge in column P of the\nwhat assumptions were used. Currently all that is spreadsheet, which means that they gave a land area\nhiding in spreadsheets and supplementary for their pledge, not only number of trees (the notes\nmaterial, but it’s critical to elevate the\nassumptions used to the main text if the paper’s tab of the spreadsheet now directs people where to\nconclusions are to be supported. find this information).\nWe agree with the reviewer that a pledge made as\nnumber of trees is very difficult to translate to a land\narea. For this reason, we prioritised direct or emissions-\nbased approaches, only basing our land area\ncalculations on number of trees if no other quantifiable\ninformation was available (Indirect pledges also include\nproportion of country or forest area, which is relatively\nreliable information). In the end 24 country pledges\nwere quantified via indirect approaches (column P of\nthe spreadsheet) and only 13 of these were based on\nnumber of trees as indicated in column H of the\nspreadsheet where the relevant tree density is given,\nwith source data in the Removals Factor tab. Of these,\nonly 2 pledges based on tree-density are over 1 million\nha – South Sudan and Uganda – which reflects 0.3% of\nour results, hence we have minimised overestimation\nof land from the tree-density approach.\nWe have also included a sensitivity analysis which\ncalculates all pledges that are not directly stated based\non a global average removal factor, which results in a\n10% increase in land area.\nSimilarly, Russia’s importance to the overall #6\ngeographic distribution of land in climate pledges We have added our calculation notes to the\n(33% of the total) would be particularly important spreadsheet, which answers the reviewer’s question.\nto understand how the estimate was derived, Russia’s pledge states: “the absorptive capacity of\nsince it was not a direct pledge of land area. How managed ecosystems is expected to increase from the\ndoes a pledge to “more than double the current 535 million tons of carbon dioxide equivalent\nabsorptive capacity of managed ecosystems” to 1,200 million tons of carbon dioxide equivalent in\ntranslate into the assumptions made by the forestry”, which is now included in column T of the\nauthors to arrive at the land area needed? These spreadsheet. On page 8 we characterise this as “more\ncountry pledges may be designed to be vague on than double”, but Russia’s pledge is emissions-based,\npurpose, and that point could be made in the meaning the steps to quantify the required land area\npaper. were relatively straightforward based on default\nremoval factors for Old Secondary forest in the boreal\nbiome, and can be seen in the spreadsheet.\nThe manuscript text on pages 8-9 is intended as a\ndiscussion of the country pledges, not a description of\nhow they were calculated.\nWe also emphasise in the discussion section that\ncountry pledges are vague, which underpins our key\nrecommendation that more transparency is needed\n(page 11, line 9).\nAnalytical approach\nI suggest the authors review national GHG #7\ninventories to understand what level of CO2 We believe the value add of this paper is in quantifying\nremovals are reported by countries, to put the land area and discussing the implications of CDR\nCDR pledges into context. pledges in terms of the scale of land that is implied.\nMany countries only report net LULUCF emissions in\ntheir GHG inventories, and so data on removals vs\nemissions is not always available - collating this\ninformation for all countries is beyond the scope of this\npaper but could be valuable for future work,\nparticularly in light of discussions about modifying\ninventory reporting (see response #9, below).\nWe have focused on quantifying the area of additional\nland that would be needed for removals to meet future\npledges – where possible we have removed the current\nLULUCF sink as the baseline (See for example US,\nCanada, EU). For example, Canada states it plans to\nincrease its land sink to 100 MtCO2 by 2050, while the\nGHG inventory reports a current LULUCF sink of 7\nMtCO2, and so we quantify the land area for 93 MtCO2\nof additional removals. This information is available in\ncolumn T of the spreadsheet.\nIt is not clear to me how the mean and standard #8\ndeviation of areas of restoration and The calculation of the mean and SD is explained in the\nreforestation were calculated in Figure 1. online methods, with further information in the SI.\nFurther clarity on this is available in the ‘source data’\nspreadsheet, containing the data and some explanation\nfor all figures, included with this resubmission.\nWe have made a reference to the online methods in\nthe Figure 1 label, so it is clearer where to find this\ninformation.\nThe authors didn’t assess bioenergy demand or #9\nquantify pledges for protection of existing forests Mitigation involving bioenergy is usually reported in\nthat would result in emission reductions, or energy sector activities of NDCs, and with the scant\ninclude CO2 removals from primary forests as detail provided regarding feedstocks and conversion\nthese are non-anthropogenic removals included in technologies, it would be very difficult to provide any\nthe terrestrial land sink. Focus is on additional C reliable estimate of associated land area. At the risk of\nsequestration specifically. More clarification overinflating the level of lands countries might rely on,\nshould be provided on how countries account for we chose not to include bioenergy. We are also clear\ncurrent CO2 removals in secondary forest and that our analysis is focused on land for CDR, and not\nplantations, vs. additional CO2 removals from the avoided emissions from protecting standing forests\n“restoration” or “reforestation” of secondary or substitution effects from bioenergy. We have\nforest. See also Nabuurs et al. 2023 reframed a section in the discussion to be clear on\n(Communications Earth and Environment) who limitations, including that our analysis does not cover\nargue that carbon dioxide fluxes from all forest these activities (Page 10 lines 23 – page 11, line 7).\nland (managed and unmanaged) need to be\nrecorded by countries in order to help track In terms of the distinction between the terrestrial land\nprogress towards global climate targets. sink and anthropogenic removals - current accounting\npractices for national inventories are to only report the\ncarbon flux on managed lands, which was introduced as\na proxy to capture anthropogenic effects as noted by\nNabuurs et al. Their recommendation to move to\ncomprehensive land sector accounting has been\ndiscussed for a long time, due to the accounting\ncomplexities and loopholes introduced by the managed\nland proxy, and now also due to the discrepancy in\nglobal estimates of the land sink between national\ninventories and climate models, as previously discussed\nby Grassi et al., 2021 (NCC) and 2023 (Earth Sys. Sci.\nData).\nHowever, our analysis is not about reporting of\nterrestrial fluxes in national GHG inventories, but rather\nabout activities pledged for future mitigation in NDC\nand LT-LEDs. There is a distinction between setting a\ntarget (as in NDCs) reporting national GHG fluxes (as in\nnational GHG inventories), and accounting towards a\ntarget (as in the ETF under the Paris Agreement). The\ncontext of the pledges we are assessing is in terms of\nwhat should be counted towards a target, not what\nshould be reported, and Nabuurs et al do not tackle the\nissue of target-setting in their paper. While the\nrecommendation to move towards comprehensive land\nsector accounting in inventories is a good one, it has\nlarger political implications in terms of what part of\nthat terrestrial flux should count against countries\nclimate targets? Delving into this complex discussion of\nterrestrial carbon accounting we believe would\novercomplicate the paper and would be very difficult to\ninclude in space limitations (Giddens et al 2023 discuss\nthis to some extent).\nTo accommodate the reviewers concerns, we have\nadded a reference to Nabuurs et al., 2023 in the\ndiscussion in reference to the need to separate land\nand energy sector targets in NDCs for greater\ntransparency, as this is what would be required in order\nto implement the comprehensive land sector\naccounting this author group calls for (see page 11, line\n21).\nUncertainty analysis: Note that removal factors #10\nand their uncertainties from IPCC 2019 We thank the reviewer for pointing this out. While we\nrefinement for temperate forests were revised in are aware of this update, we have not included the\na correction published by IPCC in July 2023. revised removal factors, because our source for\nremoval factors is Harris et al 2019 rather than IPCC.\nThe Harris et al data is based on the IPCC, but presents\nremoval factors in tonnes CO2 rather than tonnes dry\nmatter, making them more directly applicable in a\npolicy context. We believe that updating the removal\nfactors for temperate forests would make very little\ndifferent to the results, and this change will make little\ndifference to results, even though the uncertainty on\nthis particular RF is large (because it is applied to very\nfew calculation rows in our spreadsheet).\nThis may be beyond the scope of the paper, but #11\nsome reference could be made to the biophysical\nprocesses that may enhance or diminish the\nclimate effects of carbon released or absorbed We tried to fit this in somewhere, but we feel that this\nfrom forest biomass (e.g. albedo), particularly if a is outside the scope of this paper, and could not find\nsubstantial portion of land-based CDR is expected anywhere in the discussion that it naturally fit.\nto come from temperate and boreal regions\n(Russia, Canada, USA).\nSuggested improvements\nUse active voice (We provide a first estimate” vs. #12\n“this paper provides a first estimate”) Thank you for this recommendation, we have revised to\ninclude active voice throughout the paper.\nPer Nature guidelines (I think), avoid claims of #13\nnovelty (“it provides the first assessment of its We have made this change as well as others to be\nkind”) consistent with the Nature Communications Guidelines,\nsuch as not mentioning our study until the last\nparagraph of the introduction and removing footnotes.\nAbstract and throughout: avoid vague statements #14\nlike “implying impacts on people and food We have added that the likely impacts are due to\nsecurity”. What kind of impacts? people being dispossessed of access to land and land-\nbased resources, see page 1, lines 22-23\nThis is also described in more detail page 11, lines 29-\n38with ample references.\nInclude in the introduction more context for the #15\ngeneral reader of what the Paris Agreement goal We have added this context into the introduction, see\nis – achieve a net balance between anthropogenic page 2, lines 13-16.\nemissions by sources and removals by sinks in the\nsecond half of the century. Important to include\nanthropogenic and to stress the role of forests on\nthe sinks side.\nPerhaps worth pointing out that the idea that all #16\ncountries achieving net-zero within their own Assessing the level of CDR that would be on top of\nboundaries doesn’t necessarily make sense current CDR in the land sector is exactly what we are\nbecause all countries have a different starting doing in this study. For the most part, countries make\npoint when it comes to carbon dioxide removals clear in their pledges what action is pledged as new or\non land. Some developing countries are already additional compared to current LULUCF sink or source.\nnet zero/net sinks! So it’s an important point to\nmake that to increase CO2 removals beyond\nthose that exist in the country now, we need to\nassess the level of ambition in climate pledges\nand what CDR would be on top of current CDR in\nthe land sector.\nAnother point to highlight might be how land use #17\nhistory is likely to play a role in how CDR actually We think that the reviewer makes an excellent point\nplays out – how much CDR an ecosystem can here and have included this sentence on page 11, lines\nsupport may differ from the CDR that countries 38-39: “The way that these policies play out and how\nare pledging to deliver. The way that these land is actually used will depend upon local land tenure\npolicies play out and how land is actually used will as well as other social and economic factors.”\ndepend upon local land tenure as well as other\nsocial and economic factors.\nClarity/context\n“We present a breakdown of what these #18\nremovals would look like” – this is too vague, We have edited the abstract to reflect this suggestion.\nsuggest deleting from abstract. More clear: “We\npresent a breakdown of how demands for land\nwould be distributed geographically and over\ntime”\n“For more than half of this area, the pledges #19\nenvisage the conversion of existing land-uses to Our classification of land use activities into those\nforests, while the remaining area is for restoration involving land-use change or those involving\nof degraded ecosystems.” What is a “degraded restoration (such as managed forest remaining forest)\necosystem” as defined by various countries? How is illustrated in Table 2 is now better explained on page\nmuch overlap is there between existing land uses 5, and in the online methods, in response to comment\n(several of which are degraded from their natural #4.\nstate) and degraded ecosystems? Not clear how\nthis breakdown was determined after reading We are using the land use change / restoration divide\nthrough the methods. as a proxy to indicate where CDR may be more or less\nproblematic. It is obviously not exact to each country\ncircumstance and land use history given the lack of\ninformation in NDCs and we have underscored the\nvagueness of pledges and the need for more detail and\ntransparency in mitigation commitments at several\npoints in the paper.\nNot clear how land for reforestation/plantations #20\nfor BECCS is calculated Countries that included BECCS in their pledges did not\nstate what the biomass feedstock would be, as we note\non page 6, line 10. Hence, we assumed forest\nplantations for the bioenergy feedstock, meaning the\ncalculation to convert tonnes removed via BECCS was\nthe same as converting tonnes removed via plantations\n(using the relevant biome removal factor for\nplantations based on the country). We have added a\nsentence at page 6, line 12 to make this link between\nassuming BECCS feedstock as plantations and\ncalculating land area for plantations clearer.\nIntroduction: “many climate mitigation #21\napproaches that rely on land, such as large-scale We thank the review for this suggestion and have\nafforestation, threaten to exacerbate rather than implemented this change on page 2, line 19.\naddress the biodiversity crisis.” Change to “some”\napproaches, as many climate mitigation\napproaches that rely on land have positive\nbiodiversity benefits if implemented well.\nReviewer #2:\nThe paper, entitled \"Over-reliance on Land for We thank the reviewer for these comments\nCarbon Dioxide Removal in National Climate\nPledges\", makes a significant and relevant\ncontribution to the climate policy literature,\nfocusing on the assessment of land requirements\nfor land-based mitigation options and the\nassociated risks. As a publication based on the\nanalysis of the \"Land Gap Report\", it provides a\ntimely contribution to the scientific literature,\nesp. in the context of next NDCs due in 2025.\nHowever, there are several issues that require\nattention and major revisions before publication.\n1.Relevance of the documents for domestic\nclimate policy making:\na. There is a flurry of analyses of NDCs and LT- #22\nLEDS. What is usually missing is a reflection on the We thank the reviewer for this insight. We have\npolitical role of these documents. The lack of reconsidered the framing of the paper and agree\nsubmitted LT-LEDS, for example, indicates the low that it is treating the climate pledges as factual\npolitical priority that UNFCCC signatories attach statements. We have added a new paragraph to\nto these reporting mechanisms. It should be the introduction that discusses the political\nemphasised that not only is the implementation context of the pledges, in terms of presenting\ngap between actual policy and NDC/LT-LEDS ambition that may not be realised (See page 2,\nhuge, but also that these strategy documents from line 45 on). One aspect of understanding\nhave limited relevance for national climate how realistic these pledges are, however, is to\npolicies and that these political contexts for specific pledges cannot be identified from these understand the land area that is embedded in\ndocuments. This is not to say that a quantitative CDR claims, which is the objective of this paper.\nanalysis of the documents should not be done,\nbut the framing of such an analysis should take In addition, we have used more conditional\ninto account this limitation arising from the data language throughout the paper when talking\ninto account this limitation arising from the data about land in climate pledges that may or may\nsource of strategy documents that may not fully not be realised.\nreflect a country's policy priorities.\nb. The paper should provide additional #23\ninterpretation and policy contextualisation, The discussion on page 8 is intended to provide\nparticularly regarding the high numbers from policy contextualisation for the countries with\nindividual countries, such as Russia. This will help very large land area pledges, but this is very brief\nto interpret the high headline number reported at due to space limits making it difficult to discuss\nthe beginning of the paper. multiple national contexts. We have expanded\nthis discussion (see page 8-9), but help interpret\nthe headline number we have also:\n- Added a sentence to the introduction that\ndraws attention to the small number of\ncountries responsible for the majority of\nresults (Page 3, lines 17-18)\n- Added the notes regarding calculation\nassumptions to the spreadsheet (see column\nT) which shows how the calculations were\nmade for all countries.\n2.Methodology:\na. The methodology used to extract data from the #24\ndocuments should be clarified. At present, the We have clarified how the calculations were done\nsupplementary material lists the sources of the by adding a notes Coloumn (T) to the land\ndocuments and calculations but not the exact calculator spreadsheet which explains the\nwording on which the calculations are based. This\nmakes it difficult to trace the commitments and assumptions behind the calculations for each\ncheck for consistency and accuracy. spreadsheet row.\nb. The paper currently categorises all types of #25\nland restoration as mitigation/CDR commitments. We have revised the paper to make it clearer that\nGiven that land has been managed for a long time we don’t categorise all land restoration as CDR,\nand that objectives have changed (e.g. combating we have only quantified land area that is included\ndesertification, biodiversity,...), it might be worth in the mitigation component of country pledges.\nreflecting that CDR may not be the primary We do not include in results land that is only\nobjective of all the pledges collected here, but included in adaptation pledges, or non-climate\ncould also be a side-effect/co-benefit of an restoration pledges. Many countries have made\ninitiative that policy makers had in mind for other restoration pledges under the Bonn Challenge or\nreasons - it may not be all about CDR. It would be other initiatives, or significant land sector policies\nuseful to distinguish between pledges that are in the adaptation component of their NDCs,\nexplicitly focused on carbon removal and those which we don’t include.\nwhere CDR is a secondary or co-benefit. This\nclarification will provide a better understanding of The difference, and likely partial overlap, between\nthe nature and intent of the pledges. climate pledges and other restoration\ncommitments is explained on page 7, lines 4-15.\nWe have made revisions here, and in the\nintroduction and where results are first\nintroduced to clarify that the pledges we assessed\nare only from the mitigation component of NDCs.\nThe reviewer is correct that some of the\nmitigation pledges reflect other land sector\npriorities than CDR (such as agricultural\nregeneration and food security), but as they have\nbeen included in the mitigation component of\npledges, the country is indicating they will count\nthe CDR from these activities towards their\nclimate mitigation targets.\nc. Related to Issue 1: The use of government #26\ndocuments (instead of NDC/LT-LEDS in the We have used NDC/LT-LEDS for all countries but 2\nanalysis should be explained (why are – Saudi Arabia and Kazakhstan. Both of the\ngovernment documents used in some cases?) documents we use for these countries are\nThere are significant gaps between NDCs/LT-LEDS presidential speeches that announce\nand actual national policy making (see also Issue reforestation initiatives as part of climate plans.\n1). This should be better explained - or focus on They are confirmed and public plans, but not\nonly one type of document. Alternatively, the included in NDC/LT-LEDS yet as these are not\npaper could consider focusing on one type of frequently updated.\ndocument to provide a more consistent analysis.\nThe information on which pledges are official\nNDC/LT-LEDS or unofficial pledges in other\ngovernment documents is in column S. Several\nentries that had not been updated from unofficial\nto official are now fixed.\n3. Permanence/reversibility of CDRs:\na) The issue of reversibility and different #27\npermanence periods for different types of We thank the reviewer for this suggestion and\nsequestration is critical, but is not addressed in agree that it is an important issue, and is one of\nthe pledges and is not explicitly raised in the the key messages of the Land Gap report work,\npaper. Given the aim of the paper to inform the underlying this paper.\nreview of NDCs, it is important to highlight the\nchallenges associated with relying on LULUCF- We have now added a sentence on this in the\nbased CDR to meet climate goals. The potential discussion with a recent reference (page 10, line\nmeasures to incorporate them into CDR policy, 21-22), but due to space constraints cannot\nsuch as buffer pools and equivalence discounting, expand on this issue in the paper.\nshould be raised to highlight that land\nrequirements could be even higher if LULUCF-\nbased CDR is responsibly governed to meet\nclimate goals.\nIn conclusion, the paper makes an important We hope that the revisions outlined above have\ncontribution to climate policy by addressing the adequately addressed the reviewers concerns and\nrole of land-based mitigation options in national have improved the paper.\nclimate commitments. In order to improve the\nrelevance of the paper, it is recommended that\nthe above issues are addressed in a major\nrevision. By doing so, the paper can provide a\nmore comprehensive and insightful analysis of the\nissue and have a greater impact on the climate\npolicy discourse\nReviewer #3 :\nReviewer #3 (Remarks to the Author):\nI noted reading this paper and consider it a very #28\nworthwile contribution. We thank the reviewer for these comments, we\nThe paper evaluates the scale and potential land- particularly agree that the lack of coordination\nuse conflicts (and other challenges) for nations to between reporting on progress towards different\ndeliver on pledges around LULUFC and BECCCS. I environmental conventions is problematic.\naddresses and highlights the uncertainty and risk\nof presenting these land pledges in the absence of\nrobust local assessment and especially spatial\nanalysis. The same risk applies to national pledges\nas they pertain to energy efficiency, renewable\nenergy expectations, and CCUS (especially\nstorage). This lack of spatial grannularty obscures\na multitude of risks and uncertainties when it\ncomes to resource capacities, environmental\nconsiderations and local values.\nIn the case of the land sector, the lack of\ncoordination between different environmental\nconventions is especially problematic. The paper\nis timely, as we approach COP28, proposals to\nupdate NDCS, and the IAMs modelling updates\nahead of the 7th Assessment Report.\nAcknowledging that I am not an expert in land #29\nsector analysis, the analytical work done appears\nrobust and uses sound sources. The authors also We have improved the analytical work done in\nacknowledge clearly the uncertainties and the paper through including the calculation\nlimitations on the analysis but I agree they have assumptions in the spreadsheet (column T), and\nlanded at a conservative place.\nthrough conducting a sensitivity analysis which\nshows that our choice of removal factors and\nforest biomes does not significantly drive the\nresults.\nThe paper is also very well written. I had a couple #30\nof very minor comments: Thank you, we have implemented this idea and\nOn page 6, where the authors write: \"For made other similar small edits.\nexample, the global land rush of the 2000s, which\nwas seen as a great threat to small scale farmers,\nsaw no more than seven million ha being\ntransacted per year.\" Authors could perhaps add\nsome descriptive context noting the broad\nreadership of Nature Comms. E.g.:\n\"For example, the global land rush of the 2000s\nfor the purpose of industrial-scale agriculture and\nresource extraction…, which was seen as a great\nthreat to small scale farmers, saw no more…\"\nAlso suggest the insertion of \"approximatey\" or #31\n\"around\" in a number of places, given the We have added more conditional language to the\nacklnowldged uncertainty in parameter. e.g. abstract and intro to indicate that the estimated\n\"Saudi Arabia has pledged to plant an additional land area would be required if these pledges are\n40 billion trees in neighbouring countries, implemented.\nequivalent to (around) 200 million ha\".\nOtherwise I recommend for publication. We have added language to indicate the pledges\nfrom Saudi and others are approximate.\nResponse to review – Over-reliance on land for carbon dioxide removal in national climate\npledges\nReviewer #2:\nDear authors,\nthanks for the careful revision of paper and\nconsidering the points rasised by the reviewers.\nThe improved transparency in the methods and\nthe new framing about lack of data/details in\nthe pledges improve the paper.\nTwo minor things I'd like to raise: Thanks for pointing this out, we have corrected\n- the direct quote from the PA is not the excact the quote.\nquote (at least not from Art. 4\n-I think in the supplementary material are a Thanks again, we have cleaned up the\nfew notes (eg. U6, Z29) and colour (AF17) that supplementary data sheet.\nshould be deleted before publication\nReviewer #4:\nThe paper evalutes the reliance on land for CDR\nin national climate pledges. I generally find this\ntopic to be highly important and the results\nnoteworthy. The article is likely to have an\nimpact on the field. I found results largely\nsupported by data, although I think some\nrevisions are needed. I provide some comments\nbelow. Thank you for the interesting read.\n1. BECCS pledges seem unlikely to be forest We agree with the reviewer that BECCS\nfeedstocks. In general, biomass residues are very pledges are unlikely to be met by forest\nimportant in ramping-up biomass supply at low feedstocks, and we state clearly in the paper\nlevels of demand, whilst dedicated bioenergy that we are only using this as a proxy removal\ncrops dominate when demand exceeds 100 EJ factor, which we expect would have a similar\nyear-1 (Hanssen et al., 2020). The energy yields rate to bioenergy feedstocks.\nof short-rotation bioenergy crops exceed\nmanaged forests. Lignocellulosic bioenergy crops However, we take the reviewer’s point that\nare considered in nearly every IAM, and this is an inadequate solution. At the same\nmanaged forestry for bioenergy is often excluded time, we do not agree that we should be\ndue to sustainability issues (Daioglou et al., modelling the variability for BECCS land area\n2020). Sugarcane cultivation is a key contributor requirements depending on different\nto modern bioenergy supply (Ramirez Camargo feedstock options, or investigating what is\net al.). It cannot be assumed that BECCS biomass most likely at a country level. We have\nsupply will be coming from forest plantations or already made extensive revisions to\nclaim that this is the most conservative land use accommodate reviewer 1’s concerns that\nestimate, please revise text and calculations. these pledges should not be interpreted as\nThere is a need to go down to country-level reality and it is a key message of our paper\ndetail and identify the most likely feedstock, and that government pledges, if they are to be\nmaybe also do some different scenarios with taken seriously, should include the expected\nvarying feedstocks (residues, energy crops, etc.). land area required for implementation of the\nI think data from Li et al. (2018) or Li et al. (2020) various CDR options they include.\ncould be useful.\nTo avoid conveying a message that standing\nDaioglou, V., Rose, S.K., Bauer, N. et al. Bioenergy forests are likely to or should be used as\ntechnologies in long-run climate change BECCS feedstocks, we believe the best\nmitigation: results from the EMF-33 study. solution here is one which represents an\nClimatic Change 163, 1603–1620 (2020). average global value for BECCS capture rates,\nhttps://doi.org/10.1007/s10584-020-02799-y as well as yields, conversion efficiencies,\nresource input, etc . After investigating\nHanssen, S.V., Daioglou, V., Steinmann, Z.J.N. et several sources, we have decided to use a\nal. Biomass residues as twenty-first century mean value for 2030-2050 from the LPJ-Guess\nbioenergy feedstock—a comparison of eight model (Krause et al 2019).\nintegrated assessment models. Climatic Change\n163, 1569–1586 (2020).\nhttps://doi.org/10.1007/s10584-019-02539-x This value changes the removal factor from\nbetween 11-13 tCO2/ha/yr for the 5 countries\nLi, W., Ciais, P., Stehfest, E., van Vuuren, D., for which we have quantified results for\nPopp, A., Arneth, A., Di Fulvio, F., Doelman, J., BECCS to 10.1 tCO2/ha/year, increasing the\nHumpenöder, F., Harper, A. B., Park, T., total land area needed for BECCS from 74 to\nMakowski, D., Havlik, P., Obersteiner, M., Wang, 82 million hectares.\nJ., Krause, A., and Liu, W.: Mapping the yields of\nlignocellulosic bioenergy crops from observations We do not assume any of this feedstock is\nat the global scale, Earth Syst. Sci. Data, 12, 789– met with residues as analysis suggests residue\n804"}, {"round": 2, "reviewer_comments": {"reviewer_2": "Dear authors,\nthanks for the careful revision of paper and considering the points rasised by the reviewers. The improved transparency in the methods and the new framing about lack of data/details in the pledges improve the paper.\nTwo minor things I'd like to raise:\n- the direct quote from the PA is not the excact quote (at least not from Art. 4\n- I think in the supplementary material are a few notes (eg. U6, Z29) and colour (AF17) that should be deleted before publication\nKind regards", "reviewer_4": "The paper evalutes the reliance on land for CDR in national climate pledges. I generally find this topic to be highly important and the results noteworthy. The article is likely to have an impact on the field. I found results largely supported by data, although I think some revisions are needed. I provide some comments below. Thank you for the interesting read.\n1. BECCS pledges seem unlikely to be forest feedstocks. In general, biomass residues are very important in ramping-up biomass supply at low levels of demand, whilst dedicated bioenergy crops dominate when demand exceeds 100 EJ year-1 (Hanssen et al., 2020). The energy yields of short-rotation bioenergy crops exceed managed forests. Lignocellulosic bioenergy crops are considered in nearly every IAM, and managed forestry for bioenergy is often excluded due to sustainability issues (Daioglou et al., 2020). Sugarcane cultivation is a key contributor to modern bioenergy supply (Ramirez Camargo et al.). It cannot be assumed that BECCS biomass supply will be coming from forest plantations or claim that this is the most conservative land use estimate, please revise text and calculations. There is a need to go down to country-level detail and identify the most likely feedstock, and maybe also do some different scenarios with varying feedstocks (residues, energy crops, etc.). I think data from Li et al. (2018) or Li et al. (2020) could be useful.\nDaioglou, V., Rose, S.K., Bauer, N. et al. Bioenergy technologies in long-run climate change mitigation: results from the EMF-33 study. Climatic Change 163, 1603–1620 (2020). https://doi.org/10.1007/s03066150-020-02799-y\nHanssen, S.V., Daioglou, V., Steinmann, Z.J.N. et al. Biomass residues as twenty-first century bioenergy feedstock—a comparison of eight integrated assessment models. Climatic Change 163, 1569–1586 (2020). https://doi.org/10.1007/s03066150-019-02539-x\nLi, W., Ciais, P., Stehfest, E., van Vuuren, D., Popp, A., Arneth, A., Di Fulvio, F., Doelman, J., Humpenöder, F., Harper, A. B., Park, T., Makowski, D., Havlik, P., Obersteiner, M., Wang, J., Krause, A., and Liu, W.: Mapping the yields of lignocellulosic bioenergy crops from observations at the global scale, Earth Syst. Sci. Data, 12, 789–804", "reviewer_author_response": "Response to review\nThank you for the improvements made to the manuscript. The soil carbon sensitivity for selected activities was appreciated. I note that several of my comments were not acted upon, and in some cases solid justification was given. However, other aspects still requires revisions.\n\nThe results presented here are very similar to the Land Gap Report. Several figures contain similar data. More care should be taken to provide citations to the Land Gap report where there is clear overlap, including for data in individual figures. Examples include figure 2 and figure 3 in the manuscript. E.g., figure 1 in the 2023 land gap report that shows land required for CDR in national climate pledges, which is a different way to visualize the data shown in Figure 3 in the submitted manuscript. It even states some of the same/similar country-shares (for example, Russia 35%, US 12%, Saudi 20%). Figure 3 in the 2023 land gap report is like Figure 2 in the submitted manuscript (both figures include data on land requirements and number of countries).\n\nhttps://landgap.org/downloads/2022/Land-Gap-Report_FINAL.pdf\nhttps://landgap.org/downloads/2023/Land-Gap-Report_2023-Briefing_FINAL.pdf\n\nBECCS calculations still have major improvement potential. It is too simple for a paper addressing land requirements of CDR. Using a global average BECCS carbon removal rate based on LPJ-Guess to quantify national-level BECCS land requirements does not follow state-of-the-art methods, considering all the spatial yield data that is available from multiple sources (including LPJ-Guess). On top of that, comes opportunities to utilize land-free bioenergy feedstocks (see for example, Wu et al.). I agree that a change in approach is unlikely to affect the main conclusion of the paper (e.g. over-reliance of land in pledges) considering the importance of reforestation and restoration, but it will affect sub-results and sub-findings that support the main conclusion including all BECCS results. Currently, the national-level results and land requirements for the five countries with BECCS pledges has low value, perhaps especially important for the US pledge. It still needs revision.\n\nWu, F., Pfenninger, S., & Muller, A. (2024). Land-free bioenergy from circular agroecology—a diverse option space and trade-offs. Environmental Research Letters, 19(4), 044044.\n\nUsing nation-specific yields would already help. As noted below, it makes more sense to consider second generation energy crops in 2050 than first generation. And a quantitative basis for the discussions on implications of different bioenergy feedstocks on land requirements should be provided.\n\nI note that recently published research has provided scenario analysis of the land use implications of the NDCs for a SSP2 scenario (SSP2-NDC). I think that the insights provided there considering how NDCs affects future land use is important and merits a mention here. E.g., in SSP2-NDC increased forest cover towards 2060 comes at the expense of rangeland and other natural land (nonforested ecosystems, shrublands, deserts). Also note that the net land use change towards forests and BECCS seems lower than the land requirements quantified here.\n\nHumpenöder, Florian, et al. \"Food matters: Dietary shifts increase the feasibility of 1.5° C pathways in line with the Paris Agreement.\" Science Advances 10.13 (2024): eadj3832. https://doi.org/10.1126/sciadv.adj3832\n\nSome specific comments:\nPlease note that line numbers refer to the manuscript version without track changes.\n\nP.2 Lines 21-24, and several other places in different sections in the manuscript addresses/discusses impacts on biodiversity. CDR may help hinder irreversible biodiversity losses caused by increasing temperatures that leads species niche limits to exceed (see Trisos et al.). The manuscript does a very good job in highlighting the sustainability risks of land use change. I think there is wide agreement that CDR should not be used as an excuse to avoid emission cuts (e.g., p9 lines 41-47). However, the lack of a discussion of the wider benefits of achieved land-based mitigation from CDR on the same sustainability indicators makes the communication too one sided (see Hirata et al. for a thorough analysis of land-based CDR biodiversity implications). I’d like to see some more nuance in the discussions.\n\nHirata, A., Ohashi, H., Hasegawa, T. et al. The choice of land-based climate change mitigation measures influences future global biodiversity loss. Commun Earth Environ 5, 259 (2024). https://doi.org/10.1038/s43247-024-01433-4\nTrisos, C.H., Merow, C. & Pigot, A.L. The projected timing of abrupt ecological disruption from climate change. Nature 580, 496–501 (2020). https://doi.org/10.1038/s41586-020-2189-9\n\nP.5 Lines 18-26. The simple approach of using a global average rate for BECCS is inconsistent with the attempt to capture some locality that is done for restoration and reforestation. It also disregards a lot of work done to spatially model energy crops over the last couple of decades, including using the LPJ family of models (LPJ-Guess mentioned and cited in-text). The approach used here does not follow state-of-the-art. It is something that could be easily improved, and that also should be improved. Chosen approach might not be expected to change your main conclusion (e.g., over-reliance on land in climate pledges), but it does affect sub-results and sub-findings that supports the totality. A key example is United States and results in Figure 3. I re-iterate the need to improve the modelling of bioenergy crops and to capture effects of locality for the five countries with BECCS pledges.\n\nP5. Lines 19-22. As a more concrete example, you could for example point to that Switzerland and UK could meet a share of their BECCS pledges with no land requirements by implementing CCS in incinerators (waste-to-energy, also true for other countries). See Rosa et al. for a quantification, I suggest comparing emission pledges to country-specific potentials.\n\nRosa, L., Sanchez, D. L., & Mazzotti, M. (2021). Assessment of carbon dioxide removal potential via BECCS in a carbon-neutral Europe. Energy & Environmental Science, 14(5), 3086-3097. https://doi.org/10.1039/D1EE00642H\n\nP.5 Lines 27-30. It is unclear why bioenergy should be separated into energy sector pledges and BECCS pledges. Cannot these pledges perfectly align, as BECCS is a multi-functional process which both produces energy and delivers negative emissions? In some cases, as for wastes (for example, CCS in incinerators or biomethane production with CCS), it may even serve at least three functions, including waste treatment, energy production, and delivery of negative emissions.\nNote that there are 119 ongoing CCS projects under development in Europe, several which involve incinerators.\nLevina, E., Gerrits, B., & Blanchard, M. (2023). CCS in Europe – Regional Overview. Global CCS Institute. https://www.globalccsinstitute.com/resources/publications-reports-research/ccs-in-europe-regional-overview/\n\nP5 lines 23-24 and P11 lines 14-15. Does Krause et al. (2019) that you rely on for bioenergy capture rates from LPJ-Guess specifically address bioenergy and first-generation energy crops (edible feedstocks)? I see no clear indication of it, neither in the article, in their SI, or in the data published on Figshare. Did I miss something, or is this the wrong citation (is it really Krause et al. (2018)?)? I guess Krause et al. (2019) quantifies NPP of some plant functional types, but these were probably not parameterized as typical bioenergy feedstocks. Please clarify how Krause et al. was used.\n\nKrause, A., V. Haverd, B. Poulter, P. Anthoni, B. Quesada, A. Rammig, and A. Arneth. “Multimodel Analysis of Future Land Use and Climate Change Impacts on Ecosystem Functioning.” Earth’s Future 7, no. 7 (July 2019): 833–51. https://doi.org/10.1029/2018EF001123.\nKrause, A. et al. Large uncertainty in carbon uptake potential of land-based climate-3 change mitigation efforts. Glob Change Biol 24, 3025–3038 (2018).\n\nAs all the BECCS pledges are for 2050 (according to land calculator), it is surprising to rely on first-generation crops and not second generation. Daioglou et al. highlights that lignocellulosic crop (including miscanthus, willow, and eucalyptus) dominates future bioenergy supply in IMAGE scenarios, whilst edible crops play a minor role (see fig. 7). The same also happens in other models. Also, unclear why irrigated crops were chosen and not rain-fed, especially since water scarcity risks were previously highlighted.\n\nDaioglou, Vassilis, et al. \"Integrated assessment of biomass supply and demand in climate change mitigation scenarios.\" Global Environmental Change 54 (2019): 88-101. https://doi.org/10.1016/j.gloenvcha.2018.11.012\n\nAs an example on the importance of crop types, Li et al. predicts with machine learning techniques a global mean yield of 16.3 tDM ha-1 yr-1 for lignocellulosic crops, which may correspond to about 8 tC ha-1 yr-1 (or sequestered 30tCO2 ha-1 yr-1) harvested. If 90% of this is captured in a thermal power plant, then this is nearly 3x higher removal rate than the value used in your work (10.1 tCO2 ha-1 yr-1, Table S1) from Krause et al 2019 and way outside the ranges used in the uncertainty analysis.\n\nLi, Wei, et al. \"Mapping the yields of lignocellulosic bioenergy crops from observations at the global scale.\" Earth System Science Data 12.2 (2020): 789-804. https://doi.org/10.5194/essd-12-789-2020\n\nP5, lines 25-26. And IAMs show lower yield values for second generation bioenergy crops in comparison with the random forest model from Li et al. cited above (see fig 5). IAM yield maps (IMAGE, Magpie, GLOBIOM) also underestimate yields relative to field observations (see fig 6, Li et al.). Are you sure it is right to “give the impression” that IAMs rely on too high energy crop yields?\nAlso, text says there is more information in SI, but I did not find any.\n\nP.5 line 25. IAM abbreviation not spelled out previously, should remove abbreviation and spell out. Might need to spend a few words describing what these models are as well.\n\nP6, lines 11.13. According to Bluwstein & Cavanagh, the land acquisition peak in 2011 was about 12.4 Mha yr-1, not 7 Mha yr-1. See fig. 10. Also, should specify that this is Global South only, and not worldwide. If a mean is taken over a period around 2011, then 7Mha could be right, but then please specify the year range. Strongly recommend comparing against remotely sensed data in addition, see for example the Hilda+ paper (Winkler et al.). It shows annual changes in the 2000s between 6-11 Mha yr-1 (see fig3).\n\nBluwstein, J., & Cavanagh, C. (2022). Rescaling the land rush? Global political ecologies of land use and cover change in key scenario archetypes for achieving the 1.5 °C Paris agreement target. The Journal of Peasant Studies, 50(1), 262–294. https://doi.org/10.1080/03066150.2022.2125386\nWinkler, K., Fuchs, R., Rounsevell, M. et al. Global land use changes are four times greater than previously estimated. Nat Commun 12, 2501 (2021). https://doi.org/10.1038/s41467-021-22702-2\n\nA follow up question to this. How good of a proxy is land acquisition / transactions as a land-use change indicator? My guess is that it is far from perfect. Re-iterate the need to consider remote sensing products.\n\nP7. Line 5. 322 million ha is the mean (not specified)? Also, across what scenarios? SSPs in combination with RCP-1.9?\n\nP7 Line 8. Provide the full range here as well? The complete feasibility space is important. These pathways should not be viewed as a statistical sample (see Huppmann et al., box 1).\n\nHuppmann, D., Rogelj, J., Kriegler, E. et al. A new scenario resource for integrated 1.5 °C research. Nature Clim Change 8, 1027–1030 (2018). https://doi.org/10.1038/s41558-018-0317-4\n\nP.7 lines 46-48. Refers to the grain-for-green programme? Perhaps, it should be mentioned directly.\n\nP.9 Lines 18-19. This depends on where forest expansion happens. Too unspecific, please spend some more words to explain.\n\nP9. Line21-22. Should differentiate between increases in forest cover for carbon removal and increases in land area for energy crops. This statement is only right for forest cover, not for energy crops (see page 7, lines 3-9). These two land uses do not serve the same functon(BECCS can be used both for energy and CDR).\n\nPage 9. Lines 41-43. Land requirements of future food production or biodiversity impacts have not been modelled here quantitatively, so how robust is this conclusion? As it stands now, it seems like qualitative speculation with insufficient support. Note that in contrast Xu et al. highlights that delaying implementation of land-based mitigation measures may threaten food security due to feedback loops on global warming. Some comparisons with quantitative studies may be needed to make this conclusion (planetary boundaries? Hirata et al. cited above?). Should have a look at Humpenöder et al. fig 6 showing some expected loss of natural area in SSP2-NDC.\n\nXu, S., Wang, R., Gasser, T. et al. Delayed use of bioenergy crops might threaten climate and food security. Nature 609, 299–306 (2022). https://doi.org/10.1038/s41586-022-05055-8\nHumpenöder, Florian, et al. \"Food matters: Dietary shifts increase the feasibility of 1.5° C pathways in line with the Paris Agreement.\" Science Advances 10.13 (2024): eadj3832. https://doi.org/10.1126/sciadv.adj3832\n\nAlso note that many scenarios with major expansion of land-based mitigation involves agricultural intensification and a decrease in pasture area to free land for mitigation purposes. The latter relies on dietary shifts. This strategy can help avoid sustainability impacts.\n\nP10. Lines 3-5. The justification for this statement (\"unrealistic targets\") is to my impression primarily based on previous land use change rates. This argument needs to be repeated here again for more clarity.\n\nP.11 Line 35. Specify Table S2?\n\nP11. Lines 30-37. How have you accounted for uncertainty in FAO reported forest extent for indirect pledges? Is it included in the error bar shown in Fig 1b? This did not become clear to me after checking the land calculator either. FAO data on forests generally seems somewhat disputed, Lesiv et al. and Bastin et al. both show higher forest cover compared to FAO FRA data.\n\nLesiv, M., Schepaschenko, D., Buchhorn, M. et al. Global forest management data for 2015 at a 100 m resolution. Sci Data 9, 199 (2022). https://doi.org/10.1038/s41597-022-01332-3 ‘\nBastin, Jean-François, et al. \"The extent of forest in dryland biomes.\" Science 356.6338 (2017): 635-638.\n\nFig 1. A land use change for bioenergy/BECCS is not equal to reforestation. Please improve visualization and differentiate. I did not find the explanation of indirect pledges very clear in the caption, perhaps spending some more words there to describe it could help. I suggest to also put some more information in the graph by stacking the bars and separating into continents or similar, although this might be a more subjective recommendation.\n\nFig. 4. Same comment as before, that bioenergy/BECCS is not reforestation (at least, affecting UK). Caption is not informative enough to understand it for a reader with limited time skimming through. Suggest providing some more detail.\n\nFor BECCS, it is unclear what carbon losses are assumed throughout the supply chain, what carbon capture efficiency is assumed, and how you deal with any supply chain leakages of CO2. Capture efficiency will vary a lot between conversion pathways such as bioelectricity, biofuel, biomethane, etc. This directly affects BECCS land use.\n\nAll the BECCS pledges are for 2050, but it is unclear what background climate was used to produce LPJ-GUESS yields. Expected effects of climate change on yields and consequentially the land requirement should be highlighted.\n\nThe same question regarding impacts of climate change on forest growth. Harris et al. studied the past period of 2001-2019. How should climate change be expected to affect removal factors and quantified future land area requirements from emission pledges? Especially important for Russia’s major emission-based pledge in 2050?\n\nAs a final note, I would have appreciated if you could have helped me as a reviewer (with limited time available) out by referring in the rebuttal specifically to the lines were you made changes in the manuscript or by quoting the change in the rebuttal. As a reviewer, my key interest is to see what improvements were made in the manuscript, not only the response to comments.\n\nJan Sandstad Næss"}, "author_response": ""}, {"round": 3, "reviewer_comments": {"reviewer_4": "The authors have been very responsive to my comments, both by improving the paper and providing clarifications. I include some further reflections from my side that should be straightforward to address. Line numbers refer to the clean manuscript version.\nI am overall happy that the comment on bioenergy feedstock, yields, and efficiencies was taken seriously. There is now more transparency considering the relative importance of yields and what is here termed conversion efficiency (combination of carbon capture efficiencies, and other losses). The choice of a 60% conversion rate for the main results shown comes across as reasonable, as this is somewhere in between what may be expected across different conversion pathways such as for bioelectricity, biofuels, biogas, etc. Thank you for the increased clarity.\nI found the table that was included in the rebuttal on removal factors to be very useful as it exemplifies the effect of feedstock, chosen models/observations and conversion efficiency, and I recommend to include it also in the supplement to ensure coverage of a larger feasibility space. Perhaps with additional columns in the table indicating feedstock and effects on quantified land use (hectare). It is important in order to understand how results are affected by subjective choices. In fact, should probably even include another lower conversion efficiency in the range of 40-50% representing a liquid biofuel pathway (such as Fischer-Tropsch diesel), see for example Hanssen et al. Table S2 for reviewed CCS efficiencies.\nLikewise, high-end performing bioelectricity pathways achieving 80-90% conversion efficiency is a part of the feasibility space and should in my opinion be shown as a minimum in an SI. It is definitely not about making excuses for government policies, but rather to inform about the feasibility space and being rigorous.\nHanssen, S.V., Daioglou, V., Steinmann, Z.J.N. et al. The climate change mitigation potential of bioenergy with carbon capture and storage. Nat. Clim. Chang. 10, 1023–1029 (2020). https://doi.org/10.1038/s41558-020-0885-y\nAs also stated by the authors, 2nd generation energy crops have recently been implemented and parameterized in multiple DGVMs, fully coupled ESMs and similar frameworks. Thus, if country-level or biome yield data for energy crops from DGVMs or similar can be obtained I would support their use (but not a requirement). See for example:\nStenzel, F., Greve, P., Lucht, W. et al. Irrigation of biomass plantations may globally increase water stress more than climate change. Nat Commun 12, 1512 (2021). https://doi.org/10.1038/s41467-021-21640-3\nUpgraded LPJmL5 version https://www.negemproject.eu/wp-content/uploads/2021/06/NEGEM_D3.1.pdf\nCheng, Yanyan, et al. \"A bioenergy-focused versus a reforestation-focused mitigation pathway yields disparate carbon storage and climate responses.\" Proceedings of the National Academy of Sciences 121.7 (2024): e2306775121.\nLi, W., Yue, C., Ciais, P., Chang, J., Goll, D., Zhu, D., Peng, S., and Jornet-Puig, A.: ORCHIDEE-MICT-BIOENERGY: an attempt to represent the production of lignocellulosic crops for bioenergy in a global vegetation model, Geosci. Model Dev., 11, 2249–2272", "reviewer_": "n\"It is alarming that the extent of land required for CDR in government climate pledges already tracks against the upper end of mid-century scenario expectations.\"\nI note from Table 2 that land use change for reforestation is quantified as 450 Mha and for BECCS as 61 Mha.\nThen in page 8, the following is stated:\n\"Modelled pathways that limit warming to 1.5°C with no or limited overshoot show increases in forest cover for carbon removal of 322 million ha (median, with a range of -67 to 890 million ha)16. Many of these pathways also include large amounts of energy cropland area, to supply biomass for bioenergy and BECCS, with 199 (median, 56-482 range) million ha by 2050.\"\nConsidering that BECCS land requirements is only about one quarter of the median in 1.5C pathways and borders the low end of the range, I therefore propose to differentiate between land use change for increased forest cover and energy crops in p11 lines 20-21. Otherwise, the statement seems misleading.\nDaioglou, V., Rose, S.K., Bauer, N. et al. Bioenergy technologies in long-run climate change mitigation: results from the EMF-33 study. Climatic Change 163, 1603–1620 (2020). https://doi.org/10.1007/s03066150-020-02799-y\n\nfig 1. BECCS was separated, but now it is unclear what \"conditional\" and \"unconditional\" pledges in the legend means. While these two terms may be established elsewhere, they are not used anywhere else in this manuscript (I tried to search). Adding an explanation here would be helpful. Also, with current figure design, seems like BECCS fits neither conditional or unconditional? Is that correct, or should BECCS also be separated (BECCS-conditional and BECCS-unconditional, or only one of the two)?\n\nfig 3. I noticed that the source data given in column B in (\"455217_3_data_set_9406687_shhr29.xlsx\", sheet \"Figure 3 share of global land\") differs from the labels given in the figure next to country names. Fix?\n\nP.13 lines 11-13 refers to the SI for details on bioenergy country yield calculations. In the SI, in addition to providing some country-numbers (Table S1) the following is written: \"The yield uptake rates and SD for bioenergy were taken from Li et al 2020, with conversion efficiencies applied to yield uptake following Vaughan et al 2018\".\nThis short explanation is not very transparent and makes the results difficult to replicate. How did you go from gridded data from Li et al. to country-specific yields? Not sure what what was done, but a decent proxy could be to use gridded data of current cropland cover to filter and weight yield data. Also, what does the standard deviation represent, is it calculated based on spatial yield variability within the country? Do you include conversion efficiency in the SD as well? My impression is no, and if so, I really think you need to include in the SI the table from the rebuttal describing effects of yields and conversion efficiencies to better cover the feasibility space.\n\np.11 41-47. Some of these claims are still very strong with limited quantitative support from the analysis that was done. It has indeed been shown here that some large countries that rely on petroleum production have made major CDR pledges with associated land use. I am however less convinced that it has really been shown that pledges push mitigation burden onto the land sector instead of fossil fuel phase out. Although it probably is right, there is no quantitative basis here provided on emission cuts supporting the statement. Same regarding biodiversity and food security beyond land use indicators. I note that some text was shuffled around but that the message seems the exact same as in the previous manuscript version. The point made that taking land out of production in Global South may compromise food security for local populations is valid considering the geographical distribution of pledges shown, but perhaps it should be written in directly to support the claim. In contrast, I feel like the claims made in the abstract is better balanced.", "reviewer_author_response": "Response to review\nThe authors have been very responsive to my comments, both by improving the paper and providing clarifications. I include some further reflections from my side that should be straightforward to address. Line numbers refer to the clean manuscript version.\n\nI am overall happy that the comment on bioenergy feedstock, yields, and efficiencies was taken seriously. There is now more transparency considering the relative importance of yields and what is here termed conversion efficiency (combination of carbon capture efficiencies, and other losses). The choice of a 60% conversion rate for the main results shown comes across as reasonable, as this is somewhere in between what may be expected across different conversion pathways such as for bioelectricity, biofuels, biogas, etc. Thank you for the increased clarity.\n\nI found the table that was included in the rebuttal on removal factors to be very useful as it exemplifies the effect of feedstock, chosen models/observations and conversion efficiency, and I recommend to include it also in the supplement to ensure coverage of a larger feasibility space. Perhaps with additional columns in the table indicating feedstock and effects on quantified land use (hectare). It is important in order to understand how results are affected by subjective choices. In fact, should probably even include another lower conversion efficiency in the range of 40-50% representing a liquid biofuel pathway (such as Fischer-Tropsch diesel), see for example Hanssen et al. Table S2 for reviewed CCS efficiencies.\nLikewise, high-end performing bioelectricity pathways achieving 80-90% conversion efficiency is a part of the feasibility space and should in my opinion be shown as a minimum in an SI. It is definitely not about making excuses for government policies, but rather to inform about the feasibility space and being rigorous.\n\nHanssen, S.V., Daioglou, V., Steinmann, Z.J.N. et al. The climate change mitigation potential of bioenergy with carbon capture and storage. Nat. Clim. Chang. 10, 1023–1029 (2020). https://doi.org/10.1038/s41558-020-0885-y\n\nAs also stated by the authors, 2nd generation energy crops have recently been implemented and parameterized in multiple DGVMs, fully coupled ESMs and similar frameworks. Thus, if country-level or biome yield data for energy crops from DGVMs or similar can be obtained I would support their use (but not a requirement). See for example:\nStenzel, F., Greve, P., Lucht, W. et al. Irrigation of biomass plantations may globally increase water stress more than climate change. Nat Commun 12, 1512 (2021). https://doi.org/10.1038/s41467-021-21640-3\nUpgraded LPJmL5 version https://www.negemproject.eu/wp-content/uploads/2021/06/NEGEM_D3.1.pdf\nCheng, Yanyan, et al. \"A bioenergy-focused versus a reforestation-focused mitigation pathway yields disparate carbon storage and climate responses.\" Proceedings of the National Academy of Sciences 121.7 (2024): e2306775121.\nLi, W., Yue, C., Ciais, P., Chang, J., Goll, D., Zhu, D., Peng, S., and Jornet-Puig, A.: ORCHIDEE-MICT-BIOENERGY: an attempt to represent the production of lignocellulosic crops for bioenergy in a global vegetation model, Geosci. Model Dev., 11, 2249–2272"}, "author_response": ""}]

Decision letter