Editing IPCC:AR6/SRCCL/Chapter-4 (section)

== 4.5 Impacts of bioenergy and technologies for CO2 removal (CDR) on land degradation ==

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=== 4.5.1 Potential scale of bioenergy and land-based CDR ===

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In addition to the traditional land-use drivers (e.g., population growth, agricultural expansion, forest management), a new driver will interact to increase competition for land throughout this century: the potential large-scale implementation of land-based technologies for CO <sub>2</sub> removal (CDR). Land-based CDR includes afforestation and reforestation, bioenergy with carbon capture and storage (BECCS), soil carbon management, biochar and enhanced weathering (Smith et al. 2015 <sup>[[#fn:r678|678]]</sup> ; Smith 2016 <sup>[[#fn:r679|679]]</sup> ).

Most scenarios, including two of the four pathways in the IPCC Special Report on 1.5°C (IPCC 2018a <sup>[[#fn:r680|680]]</sup> ), compatible with stabilisation at 2°C involve substantial areas devoted to land-based CDR, specifically afforestation/reforestation and BECCS (Schleussner et al. 2016 <sup>[[#fn:r681|681]]</sup> ; Smith et al. 2016b <sup>[[#fn:r682|682]]</sup> ; Mander et al. 2017 <sup>[[#fn:r683|683]]</sup> ). Even larger land areas are required in most scenarios aimed at keeping average global temperature increases to below 1.5°C, and scenarios that avoid BECCS also require large areas of energy crops in many cases (IPCC 2018b <sup>[[#fn:r684|684]]</sup> ), although some options with strict demand-side management avoid this need (Grubler et al. 2018 <sup>[[#fn:r685|685]]</sup> ). Consequently, the addition of carbon capture and storage (CCS) systems to bioenergy facilities enhances mitigation benefits because it increases the carbon retention time and reduces emissions relative to bioenergy facilities without CCS. The IPCC SR15 states that, ‘When considering pathways limiting warming to 1.5°C with no or limited overshoot, the full set of scenarios shows a conversion of 0.5–11 Mkm <sup>2</sup> of pasture into 0–6 Mkm <sup>2</sup> for energy crops, a 2 Mkm <sup>2</sup>  reduction to 9.5 Mkm <sup>2</sup>  increase [in] forest, and a 4 Mkm <sup>2</sup>  decrease to a 2.5 Mkm <sup>2</sup> increase in non-pasture agricultural land for food and feed crops by 2050 relative to 2010.’ (Rogelj et al. 2018, p. 145). For comparison, the global cropland area in 2010 was 15.9 Mkm <sup>2</sup> (Table 1.1), and Woods et al. (2015) <sup>[[#fn:r686|686]]</sup> estimate that the area of abandoned and degraded land potentially available for energy crops (or afforestation/reforestation) exceeds 5 Mkm <sup>2</sup> . However, the area of available land has long been debated, as much marginal land is subject to customary land tenure and used informally, often by impoverished communities (Baka 2013 <sup>[[#fn:r687|687]]</sup> , 2014 <sup>[[#fn:r688|688]]</sup> ; Haberl et al. 2013 <sup>[[#fn:r689|689]]</sup> ; Young 1999 <sup>[[#fn:r690|690]]</sup> ). Thus, as noted in SR15, ‘The implementation of land-based mitigation options would require overcoming socio-economic, institutional, technological, financing and environmental barriers that differ across regions.’ (IPCC, 2018a <sup>[[#fn:r691|691]]</sup> , p. 18).

The wide range of estimates reflects the large differences among the pathways, availability of land in various productivity classes, types of negative emission technology implemented, uncertainties in computer models, and social and economic barriers to implementation (Fuss et al. 2018 <sup>[[#fn:r692|692]]</sup> ; Nemet et al. 2018 <sup>[[#fn:r693|693]]</sup> ; Minx et al. 2018 <sup>[[#fn:r694|694]]</sup> ).

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=== 4.5.2 Risks of land degradation from expansion of bioenergy and land-based CDR ===

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The large-scale implementation of high-intensity dedicated energy crops, and harvest of crop and forest residues for bioenergy, could contribute to increases in the area of degraded lands: intensive land management can result in nutrient depletion, over-fertilisation and soil acidification, salinisation (from irrigation without adequate drainage), wet ecosystems drying (from increased evapotranspiration), as well as novel erosion and compaction processes (from high-impact biomass harvesting disturbances) and other land degradation processes described in Section 4.2.1.

Global integrated assessment models used in the analysis of mitigation pathways vary in their approaches to modelling CDR (Bauer et al. 2018 <sup>[[#fn:r695|695]]</sup> ) and the outputs have large uncertainties due to their limited capability to consider site-specific details (Krause et al. 2018 <sup>[[#fn:r696|696]]</sup> ). Spatial resolutions vary from 11 world regions to 0.25 degrees gridcells (Bauer et al. 2018 <sup>[[#fn:r697|697]]</sup> ). While model projections identify potential areas for CDR implementation (Heck et al. 2018 <sup>[[#fn:r698|698]]</sup> ), the interaction with climate-change-induced biome shifts, available land and its vulnerability to degradation are unknown. The crop/forest types and management practices that will be implemented are also unknown, and will be influenced by local incentives and regulations. While it is therefore currently not possible to project the area at risk of degradation from the implementation of land-based CDR, there is a clear risk that expansion of energy crops at the scale anticipated could put significant strain on land systems, biosphere integrity, freshwater supply and biogeochemical flows (Heck et al. 2018 <sup>[[#fn:r699|699]]</sup> ). Similarly, extraction of biomass for energy from existing forests, particularly where stumps are utilised, can impact on soil health (de Jong et al. 2017 <sup>[[#fn:r700|700]]</sup> ). Reforestation and afforestation present a lower risk of land degradation and may in fact reverse degradation (Section 4.5.3) although potential adverse hydrological and biodiversity impacts will need to be managed (Caldwell et al. 2018 <sup>[[#fn:r701|701]]</sup> ; Brinkman et al. 2017 <sup>[[#fn:r702|702]]</sup> ). Soil carbon management can deliver negative emissions while reducing or reversing land degradation. Chapter 6 discusses the significance of context and management in determining environmental impacts of implementation of land-based options.

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=== 4.5.3 Potential contributions of land-based CDR to reducing and reversing land degradation ===

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Although large-scale implementation of land-based CDR has significant potential risks, the need for negative emissions and the anticipated investments to implement such technologies can also create significant opportunities. Investments into land-based CDR can contribute to halting and reversing land degradation, to the restoration or rehabilitation of degraded and marginal lands (Chazdon and Uriarte 2016 <sup>[[#fn:r703|703]]</sup> ; Fritsche et al. 2017 <sup>[[#fn:r704|704]]</sup> ) and can contribute to the goals of LDN (Orr et al. 2017 <sup>[[#fn:r705|705]]</sup> ).

Estimates of the global area of degraded land range from less than 10 to 60 Mkm2 (Gibbs and Salmon 2015 <sup>[[#fn:r706|706]]</sup> ) (Section 4.3.1). Additionally, large areas are classified as marginal lands and may be suitable for the implementation of bioenergy and land-based CDR (Woods et al. 2015 <sup>[[#fn:r707|707]]</sup> ). The yield per hectare of marginal and degraded lands is lower than on fertile lands, and if CDR will be implemented on marginal and degraded lands, this will increase the area demand and costs per unit area of achieving negative emissions (Fritsche et al. 2017 <sup>[[#fn:r708|708]]</sup> ). The selection of lands suitable for CDR must be considered carefully to reduce conflicts with existing users, to assess the possible trade-offs in biodiversity contributions of the original and the CDR land uses, to quantify the impacts on water budgets, and to ensure sustainability of the CDR land use.

Land use and land condition prior to the implementation of CDR affect climate change benefits (Harper et al. 2018 <sup>[[#fn:r709|709]]</sup> ). Afforestation/ reforestation on degraded lands can increase carbon stocks in vegetation and soil, increase carbon sinks (Amichev et al. 2012 <sup>[[#fn:r710|710]]</sup> ), and deliver co-benefits for biodiversity and ecosystem services, particularly if a diversity of local species are used. Afforestation and reforestation on native grasslands can reduce soil carbon stocks, although the loss is typically more than compensated by increases in biomass and dead organic matter carbon stocks (Bárcena et al. 2014 <sup>[[#fn:r711|711]]</sup> ; Li et al. 2012 <sup>[[#fn:r712|712]]</sup> ; Ovalle-Rivera et al. 2015 <sup>[[#fn:r713|713]]</sup> ; Shi et al. 2013 <sup>[[#fn:r714|714]]</sup> ), and may impact on biodiversity (Li et al. 2012 <sup>[[#fn:r715|715]]</sup> ).

Strategic incorporation of energy crops into agricultural production systems, applying an integrated landscape management approach, can provide co-benefits for management of land degradation and other environmental objectives. For example, buffers of Miscanthus and other grasses can enhance soil carbon and reduce water pollution (Cacho et al. 2018 <sup>[[#fn:r716|716]]</sup> ; Odgaard et al. 2019 <sup>[[#fn:r717|717]]</sup> ), and strip-planting of short-rotation tree crops can reduce the water table where crops are affected by dryland salinity (Robinson et al. 2006 <sup>[[#fn:r718|718]]</sup> ). Shifting to perennial grain crops has the potential to combine food production with carbon sequestration at a higher rate than annual grain crops and avoid the trade-off between food production and climate change mitigation (Crews et al. 2018 <sup>[[#fn:r719|719]]</sup> ; de Olivera et al. 2018 <sup>[[#fn:r720|720]]</sup> ; Ryan et al. 2018 <sup>[[#fn:r721|721]]</sup> ) (Section 4.9.2).

Changes in land cover can affect surface reflectance, water balances and emissions of volatile organic compounds and thus the non-GHG impacts on the climate system from afforestation/reforestation or planting energy crops (Anderson et al. 2011 <sup>[[#fn:r722|722]]</sup> ; Bala et al. 2007 <sup>[[#fn:r723|723]]</sup> ; Betts 2000 <sup>[[#fn:r724|724]]</sup> ; Betts et al. 2007 <sup>[[#fn:r725|725]]</sup> ) (see Section 4.6 for further details). Some of these impacts reinforce the GHG mitigation benefits, while others offset the benefits, with strong local (slope, aspect) and regional (boreal vs. tropical biomes) differences in the outcomes (Li et al. 2015 <sup>[[#fn:r726|726]]</sup> ). Adverse effects on albedo from afforestation with evergreen conifers in boreal zones can be reduced through planting of broadleaf deciduous species (Astrup et al. 2018 <sup>[[#fn:r727|727]]</sup> ; Cai et al. 2011a <sup>[[#fn:r728|728]]</sup> ; Anderson et al. 2011 <sup>[[#fn:r729|729]]</sup> ).

Combining CDR technologies may prove synergistic. Two soil management techniques with an explicit focus on increasing the soil carbon content rather than promoting soil conservation more broadly have been suggested: addition of biochar to agricultural soils (Section 4.9.5) and addition of ground silicate minerals to soils in order to take up atmospheric CO <sub>2</sub> through chemical weathering (Taylor et al. 2017 <sup>[[#fn:r730|730]]</sup> ; Haque et al. 2019 <sup>[[#fn:r731|731]]</sup> ; Beerling 2017 <sup>[[#fn:r732|732]]</sup> ; Strefler et al. 2018 <sup>[[#fn:r733|733]]</sup> ). The addition of biochar is comparatively well understood and also field tested at large scale, see Section 4.9.5 for a comprehensive discussion. The addition of silicate minerals to soils is still highly uncertain in terms of its potential (from 95 GtCO <sub>2</sub> yr <sup>–1</sup> (Strefler et al. 2018) to only 2–4 GtCO <sub>2</sub> yr <sup>–1</sup> (Fuss et al. 2018 <sup>[[#fn:r734|734]]</sup> )) and costs (Schlesinger and Amundson 2018 <sup>[[#fn:r735|735]]</sup> ).

Effectively addressing land degradation through implementation of bioenergy and land-based CDR will require site-specific local knowledge, matching of species with the local land, water balance, nutrient and climatic conditions, ongoing monitoring and, where necessary, adaptation of land management to ensure sustainability under global change (Fritsche et al. 2017 <sup>[[#fn:r736|736]]</sup> ). Effective land governance mechanisms including integrated land-use planning, along with strong sustainability standards could support deployment of energy crops and afforestation/reforestation at appropriate scales and geographical contexts (Fritsche et al. 2017 <sup>[[#fn:r737|737]]</sup> ). Capacity-building and technology transfer through the international cooperation mechanisms of the Paris Agreement could support such efforts. Modelling to inform policy development is most useful when undertaken with close interaction between model developers and other stakeholders including policymakers to ensure that models account for real world constraints (Dooley and Kartha 2018 <sup>[[#fn:r738|738]]</sup> ).

International initiatives to restore lands, such as the Bonn Challenge (Verdone and Seidl 2017 <sup>[[#fn:r739|739]]</sup> ) and the New York Declaration on Forests (Chazdon et al. 2017 <sup>[[#fn:r740|740]]</sup> ), and interventions undertaken for LDN and implementation of NDCs (see Glossary) can contribute to NET objectives. Such synergies may increase the financial resources available to meet multiple objectives (Section 4.8.4).

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=== 4.5.4 Traditional biomass provision and land degradation ===

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Traditional biomass (fuelwood, charcoal, agricultural residues, animal dung) used for cooking and heating by some 2.8 billion people (38% of global population) in non-OECD countries accounts for more than half of all bioenergy used worldwide (IEA 2017 <sup>[[#fn:r741|741]]</sup> ; REN21 2018 <sup>[[#fn:r742|742]]</sup> ) (Cross-Chapter Box 7 in Chapter 6). Cooking with traditional biomass has multiple negative impacts on human health, particularly for women, children and youth (Machisa et al. 2013 <sup>[[#fn:r743|743]]</sup> ; Sinha and Ray 2015 <sup>[[#fn:r744|744]]</sup> ; Price 2017 <sup>[[#fn:r745|745]]</sup> ; Mendum and Njenga 2018 <sup>[[#fn:r746|746]]</sup> ; Adefuye et al. 2007 <sup>[[#fn:r747|747]]</sup> ) and on household productivity, including high workloads for women and youth (Mendum and Njenga 2018 <sup>[[#fn:r748|748]]</sup> ; Brunner et al. 2018 <sup>[[#fn:r749|749]]</sup> ; Hou et al. 2018 <sup>[[#fn:r750|750]]</sup> ; Njenga et al. 2019 <sup>[[#fn:r751|751]]</sup> ). Traditional biomass is land-intensive due to reliance on open fires, inefficient stoves and overharvesting of woodfuel, contributing to land degradation, losses in biodiversity and reduced ecosystem services (IEA 2017 <sup>[[#fn:r752|752]]</sup> ; Bailis et al. 2015 <sup>[[#fn:r753|753]]</sup> ; Masera et al. 2015 <sup>[[#fn:r754|754]]</sup> ; Specht et al. 2015 <sup>[[#fn:r755|755]]</sup> ; Fritsche et al. 2017 <sup>[[#fn:r756|756]]</sup> ; Fuso Nerini et al. 2017 <sup>[[#fn:r757|757]]</sup> ). Traditional woodfuels account for 1.9–2.3% of global GHG emissions, particularly in ‘hotspots’ of land degradation and fuelwood depletion in eastern Africa and South Asia, such that one-third of traditional woodfuels globally are harvested unsustainably (Bailis et al. 2015 <sup>[[#fn:r758|758]]</sup> ). Scenarios to significantly reduce reliance on traditional biomass in developing countries present multiple co-benefits ( ''high evidence, high agreement'' ), including reduced emissions of black carbon, a short-lived climate forcer that also causes respiratory disease (Shindell et al. 2012 <sup>[[#fn:r759|759]]</sup> ).

A shift from traditional to modern bioenergy, especially in the African context, contributes to improved livelihoods and can reduce land degradation and impacts on ecosystem services (Smeets et al. 2012 <sup>[[#fn:r760|760]]</sup> ; Gasparatos et al. 2018 <sup>[[#fn:r761|761]]</sup> ; Mudombi et al. 2018 <sup>[[#fn:r762|762]]</sup> ). In Sub-Saharan Africa, most countries mention woodfuel in their Nationally Determined Contribution (NDC) but fail to identify transformational processes to make fuelwood a sustainable energy source compatible with improved forest management (Amugune et al. 2017 <sup>[[#fn:r763|763]]</sup> ). In some regions, especially in South and Southeast Asia, a scarcity of woody biomass may lead to excessive removal and use of agricultural wastes and residues, which contributes to poor soil quality and land degradation (Blanco-Canqui and Lal 2009 <sup>[[#fn:r764|764]]</sup> ; Mateos et al. 2017 <sup>[[#fn:r765|765]]</sup> ).

In Sub-Saharan Africa, forest degradation is widely associated with charcoal production, although in some tropical areas rapid re-growth can offset forest losses (Hoffmann et al. 2017 <sup>[[#fn:r766|766]]</sup> ; McNicol et al. 2018 <sup>[[#fn:r767|767]]</sup> ). Overharvesting of wood for charcoal contributes to the high rate of deforestation in Sub-Saharan Africa, which is five times the world average, due in part to corruption and weak governance systems (Sulaiman et al. 2017 <sup>[[#fn:r768|768]]</sup> ). Charcoal may also be a by-product of forest clearing for agriculture, with charcoal sale providing immediate income when the land is cleared for food crops (Kiruki et al. 2017 <sup>[[#fn:r769|769]]</sup> ; Ndegwa et al. 2016 <sup>[[#fn:r770|770]]</sup> ). Besides loss of forest carbon stock, a further concern for climate change is methane and black carbon emissions from fuelwood burning and traditional charcoal-making processes (Bond et al. 2013 <sup>[[#fn:r771|771]]</sup> ; Patange et al. 2015 <sup>[[#fn:r772|772]]</sup> ; Sparrevik et al. 2015 <sup>[[#fn:r773|773]]</sup> ).

A fundamental difficulty in reducing environmental impacts associated with charcoal lies in the small-scale nature of much charcoal production in Sub-Saharan Africa, leading to challenges in regulating its production and trade, which is often informal, and in some cases illegal, but nevertheless widespread since charcoal is the most important urban cooking fuel (Zulu 2010 <sup>[[#fn:r774|774]]</sup> ; Zulu and Richardson 2013 <sup>[[#fn:r775|775]]</sup> ; Smith et al. 2015 <sup>[[#fn:r776|776]]</sup> ; World Bank 2009 <sup>[[#fn:r777|777]]</sup> ). Urbanisation combined with population growth has led to continuously increasing charcoal production. Low efficiency of traditional charcoal production results in a four-fold increase in raw woody biomass required and thus much greater biomass harvest (Hojas-Gascon et al. 2016 <sup>[[#fn:r778|778]]</sup> ; Smeets et al. 2012 <sup>[[#fn:r779|779]]</sup> ). With continuing urbanisation anticipated, increased charcoal production and use will probably contribute to increasing land pressures and increased land degradation, especially in Sub-Saharan Africa ( ''medium evidence, high agreement'' ).

Although it could be possible to source this biomass more sustainably, the ecosystem and health impacts of this increased demand for cooking fuel would be reduced through use of other renewable fuels or, in some cases, non-renewable fuels (LPG), as well as through improved efficiency in end-use and through better resource and supply chain management (Santos et al. 2017 <sup>[[#fn:r780|780]]</sup> ; Smeets et al. 2012 <sup>[[#fn:r781|781]]</sup> ; Hoffmann et al. 2017 <sup>[[#fn:r782|782]]</sup> ). Integrated response options such as agro-forestry (Chapter 6) and good governance mechanisms for forest and agricultural management (Chapter 7) can support the transition to sustainable energy for households and reduce the environmental impacts of traditional biomass.

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