Editing IPCC:AR6/WGIII/Chapter-12 (section)

== 12.5 Land-related Impacts, Risks and Opportunities Associated with Mitigation Options ==

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=== 12.5.1 Introduction ===

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This section provides a cross-sectoral perspective on land occupation and related impacts, risks and opportunities associated with land-based mitigation options, as well as mitigation options that are not designated land-based, yet occupy land. It builds on Chapter 7, which covers mitigation in agriculture, forestry and other land use (AFOLU, including future availability of biomass resources for mitigation in other sectors. It complements [[#12.4|Section 12.4]] , which covers mitigation inherent in the food system, as well as Chapters 6, 9, 10 and 11, which cover mitigation in the energy, transport, building and industry sectors, and Chapters 3 and 4 which cover land and biomass use, primarily in energy applications, in mitigation and development pathways in the near- to mid-term (Chapter 4) and in pathways compatible with long-term goals (Chapter 3).

The deployment of climate change mitigation options often affects land and water conditions, and ecosystem capacity to support biodiversity and a range of ecosystem services ( [[#IPCC--2019a|IPCC 2019a]] ; [[#IPBES--2019|IPBES 2019]] ) ( ''robust evidence'' , ''high agreement'' ). It can increase or decrease terrestrial carbon stocks and sink strength, hence impacting the mitigation effect positively or negatively. As for any other land uses, impacts, risks and opportunities associated with mitigation options that occupy land depend on deployment strategy and on contextual factors that vary geographically and over time ( [[#Doelman--2018|Doelman et al. 2018]] ; [[#Hurlbert--2019|Hurlbert et al. 2019]] ; [[#Smith--2019a|Smith et al. 2019a]] ; [[#Wu--2020|Wu et al. 2020]] ) ( ''robust evidence'' , ''h'' ''igh agreement'' ) ''.''

The IPCC Special Report on Global Warming of 1.5°C (SR1.5) found that large areas may be utilised for A/R and energy crops in modelled pathways limiting warming to 1.5°C ( [[#Rogelj--2018|Rogelj et al. 2018]] ). The SRCCL investigated the implications of land-based mitigation measures for land degradation, food security and climate change adaptation. It focused on identification of synergies and trade-offs associated with individual land-based mitigation measures ( [[#Smith--2019b|Smith et al. 2019b]] ). In this section we expand beyond the scope of the Special Report on Climate Change and Land (SRCCL) assessment to include also mitigation measures that occupy land while not being considered land-based measures, we discuss ways to minimise potential adverse effects, and we consider the potential for synergies through integrating mitigation measures with other land uses, by applying a systems perspective that seeks to meet multiple objectives from multi-functional landscapes. Mitigation measures with zero land occupation, e.g., offshore wind and kelp farming, are not considered.

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=== 12.5.2 Land Occupation Associated with Different Mitigation Options ===

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As reported in Chapter 3, in scenarios limiting warming to 1.5°C (&gt;50%) with no or limited overshoot, median area dedicated for energy crops in 2050 is 1.99 (0.56 to 4.82) million square kilometres (Mkm 2 ) and median forest area increased 3.22 (–0.67 to 8.90) Mkm 2 in the period 2019 to 2050 (5–95th percentile range, scenario category C1). For comparison, the total global areas of forests, cropland and pasture (in 2015) are in the SRCCL estimated at about 40 Mkm 2 , 15.6 Mkm 2 , and 27.3 Mkm 2 , respectively (additionally, 21 Mkm 2 of savannahs and shrublands are also used for grazing) ( [[#IPCC--2019a|IPCC 2019a]] ). The SRCCL concluded that conversion of land for A/R and bioenergy crops at the scale commonly found in pathways limiting warming to 1.5°C or 2°C is associated with multiple feasibility and sustainability constraints, including land carbon losses ( ''high confidence'' ). Pathways in which warming exceeds 1.5°C require less land-based mitigation, but the impacts of higher temperatures on regional climate and land, including land degradation, desertification, and food insecurity, become more severe ( [[#Smith--2019b|Smith et al. 2019b]] ).

Depending on emissions-reduction targets, the portfolio of mitigation options chosen, and the policies developed to support their implementation, different land-use pathways can arise with large differences in resulting agricultural and forest area. Some response options can be more effective when applied together ( [[#Smith--2019b|Smith et al. 2019b]] ); for example, dietary change, efficiency increases, and reduced wastage can reduce emissions as well as the pressure on land resources, potentially enabling additional land-based mitigation such as A/R and cultivation of biomass crops for biochar, bioenergy and other bio-based products. The SRCCL ( [[#Smith--2019b|Smith et al. 2019b]] ) report that dietary change combined with reduction in food loss and waste can reduce the land requirement for food production by up to 5.8 Mkm 2 (0.8–2.4 Mkm 2 for dietary change; about 2 Mkm 2 for reduced post-harvest losses, and 1.4 Mkm 2 for reduced food waste) ( [[#Parodi--2018|Parodi et al. 2018]] ; Springmann et al. 2018; [[#Clark--2020|Clark et al. 2020]] ; [[#Rosenzweig--2020b|Rosenzweig et al. 2020b]] ) (Sections 7.4 and 12.4). Stronger mitigation action in the near term targeting non-CO 2 emissions reduction and deployment of other CDR options (DACCS, enhanced weathering, ocean-based approaches; see [[#12.3|Section 12.3]] ) can reduce the land requirement for land-based mitigation ( [[#Obersteiner--2018|Obersteiner et al. 2018]] ; [[#van%20Vuuren--2018|van Vuuren et al. 2018]] ).

Global integrated assessment models (IAMs) provide insights into the roles of land-based mitigation in pathways limiting warming to 1.5°C or 2°C; interaction between land-based and other mitigation options such as wind and solar power; influence of land-based mitigation on food markets, land use and land carbon; and the role of BECCS vis-à-vis other CDR options (Chapter 3). However, IAMs do not capture more subtle changes in land management and in the associated industrial/energy systems due to relatively coarse temporal and spatial resolution, and limited representation of land quality and feedstocks/management practices, interactions between biomass production and conversion systems, and local context, for example, governance of land use ( [[#Daioglou--2019|Daioglou et al. 2019]] ; [[#Rose--2020|Rose et al. 2020]] ; [[#Welfle--2020|Welfle et al. 2020]] ; [[#Calvin--2021|Calvin et al. 2021]] ). A/R have generally been modelled as forests managed for carbon sequestration alone, rather than forestry providing both carbon sequestration and biomass supply ( [[#Calvin--2021|Calvin et al. 2021]] ). Because IAMs do not include options to integrate new biomass production with existing agricultural and forestry systems ( [[#Paré--2016|Paré et al. 2016]] ; [[#Mansuy--2018|Mansuy et al. 2018]] ; [[#Cossel--2019|Cossel et al. 2019]] ; [[#Braghiroli--2020|Braghiroli and Passarini 2020]] ; [[#Djomo--2020|Djomo et al. 2020]] ; [[#Moreira--2020|Moreira et al. 2020]] ; [[#Strapasson--2020|Strapasson et al. 2020]] ; [[#Rinke%20Dias%20de%20Souza--2021|Rinke Dias de Souza et al. 2021]] ), they may over-estimate the total additional land area required for biomass production. On the other hand, some integrated biomass production systems may prove less attractive to landholders than growing biomass crops in large blocks, from logistic, economic, or other points of view ( [[#Ssegane--2016|Ssegane et al. 2016]] ; [[#Busch--2017|Busch 2017]] ; [[#Ferrarini--2017|Ferrarini et al. 2017]] ).

Land occupation associated with mitigation options other than A/R and bioenergy is rarely quantified in global scenarios. Stressing large uncertainties (e.g., type of biomass used and share of solar PV integrated in buildings), [[#Luderer--2019|Luderer et al. (2019)]] modelled land occupation and land transformation associated with a range of alternative power system decarbonisation pathways in the context of a global 2°C climate stabilisation effort. On a per-megawatt hour (MWh) basis, bioelectricity with CCS was most land intensive, followed by hydropower, coal with CCS, and concentrated solar power (CSP), which in turn were around five times as land-intensive as wind and solar photovoltaics (PV). A review of studies of power densities (electricity generation per unit land area) confirmed the relatively larger land occupation associated with biopower, although hydropower overlaps with biopower ( [[#van%20Zalk--2018|van Zalk and Behrens 2018]] ). This study also quantifies the low land occupation of nuclear energy, similar to fossil energy sources.

The land occupation of PV depends on the share of ground-mounted versus buildings-integrated PV, the latter assumed to reach 75% share by 2050 ( [[#Luderer--2019|Luderer et al. 2019]] ). [[#van%20de%20Ven--2021|van de Ven et al. (2021)]] assumed a 3% share of urbanised land in 2050 available for rooftop PV; [[#Capellán-Pérez--2017|Capellán-Pérez et al. (2017)]] and [[#Dupont--2020|Dupont et al. (2020)]] report 2–3% availability of urbanised surface area, when considering factors such as roof slopes and shadows between buildings, and threshold relating to energy return on investment. Land occupation of solar technologies is considered to be underestimated in studies assuming ideal conditions, with real occupation being five to ten times higher ( [[#De%20Castro--2013|De Castro et al. 2013]] ; [[#MacKay--2013|MacKay 2013]] ; [[#Ong--2013|Ong et al. 2013]] ; [[#Smil--2015|Smil 2015]] ; [[#Capellán-Pérez--2017|Capellán-Pérez et al. 2017]] ).

Production of hydrogen and synthetic hydrocarbon fuels via electrolysis and hydrocarbon synthesis is subject to conversion losses that vary depending on technology, system integration and source of carbon ( [[#Wulf--2020|Wulf et al. 2020]] ; [[#Ince--2021|Ince et al. 2021]] ) (Sections 6.4.4.1 and 6.4.5.1). Indicative electricity-to-hydrocarbon fuel efficiency loss is estimated at about 60% ( [[#Ueckerdt--2021|Ueckerdt et al. 2021]] ). The advantage of smaller land occupation for solar, wind, hydro and nuclear, compared with biomass-based options, is therefore smaller for hydrocarbon fuels than for electricity. Furthermore, biofuels are often co-produced with other bio-based products, which further reduces their land occupation, although comparisons are complicated by inconsistent approaches to allocating land occupation between co-products ( [[#Ahlgren--2015|Ahlgren et al. 2015]] ; [[#Czyrnek-Delêtre--2017|Czyrnek-Delêtre et al. 2017]] ).

Note that comparisons on a per-MWh basis do not reflect the GHG emissions associated with the power options, or that the different options serve different functions in power systems. Reservoir hydropower and biomass-based dispatchable power can complement other balancing options (e.g., battery storage, grid extensions and demand-side management ( [[#Göransson--2018|Göransson and Johnsson 2018]] ) (Chapter 6) to provide power stability and quality needed in power systems with large amounts of variable electricity generation from wind and solar power plants. Furthermore, the requirements of transport in grids, pipelines and so on differ. For example, electricity from buildings-integrated PV can be used in the same location as it is generated.

The character of land occupation, and, consequently, the associated impacts ( [[#12.5.3|Section 12.5.3]] ), vary considerably among mitigation options and also for the same option depending on geographic location, scale, system design and deployment strategy ( [[#Olsson--2019|Olsson et al. 2019]] ; [[#Ioannidis--2020|Ioannidis and Koutsoyiannis 2020]] ; [[#van%20de%20Ven--2021|van de Ven et al. 2021]] ). Land occupation associated with different mitigation options can be large uniform areas (e.g., large solar farms, reservoir hydropower dams, or tree plantations), or more distributed, such as wind turbines, solar PV, and patches of biomass cultivation integrated with other land uses in heterogeneous landscapes ( [[#Cacho--2018|Cacho et al. 2018]] ; [[#Jager--2018|Jager and Kreig 2018]] ; [[#Correa--2019|Correa et al. 2019]] ; [[#Englund--2020a|Englund et al. 2020a]] ). Studies with broader scope, covering total land use requirement induced by plant infrastructure, provide a more complete picture of land footprints. For example, [[#Wu--2021|Wu et al. (2021)]] quantified a land footprint for the infrastructure of a pilot solar plant being three times the onsite land area. [[#Sonter--2020b|Sonter et al. (2020b)]] found significant overlap of mining areas (82% targeting materials needed for renewable energy production) and biodiversity conservation sites and priorities, suggesting that strategic planning is critical to address mining threats to biodiversity ( [[#12.5.4|Section 12.5.4]] ) along with recycling and exploration of alternative technologies that use that use abundant minerals (Box 10.6).

There are also situations where expanding mitigation is more or less decoupled from additional land use. The use of organic consumer waste, harvest residues and processing side-streams in the agriculture and forestry sectors can support significant volumes of bio-based products with relatively lower land-use change risks than dedicated biomass production systems ( [[#Hanssen--2019|Hanssen et al. 2019]] ; [[#Spinelli--2019|Spinelli et al. 2019]] ; [[#Mouratiadou--2020|Mouratiadou et al. 2020]] ). Such uses can provide waste management solutions while increasing the mitigation achieved from the land that is already used for agricultural and forest production. Bioenergy accounts for about 90% of renewable heat used in industrial applications, mainly in industries that can use their own biomass waste and residues, such as the pulp and paper industry, food industry, and ethanol production plants ( [[#IEA--2020c|IEA 2020c]] ) (Chapters 6 and 11). Heat and electricity produced on-site from side-streams but not needed for the industrial processes can be sold to other users, such as district heating systems. Surplus waste and residues can also be used to produce solid and liquid biofuels, or be used as feedstock in other industries such as the petrochemical industry ( [[#IRENA--2018|IRENA 2018]] ; [[#Lock--2018|Lock and Whittle 2018]] ; [[#Thunman--2018|Thunman et al. 2018]] ; [[#IRENA--2019|IRENA 2019]] ; [[#Haus--2020|Haus et al. 2020]] ) (Chapters 6 and 11). Electrification and improved process efficiencies can reduce GHG emissions and increase the share of harvested biomass that is used for production of bio-based products ( [[#Johnsson--2019|Johnsson et al. 2019]] ; [[#Madeddu--2020|Madeddu et al. 2020]] ; [[#Lipiäinen--2021|Lipiäinen and Vakkilainen 2021]] ; [[#Rahnama%20Mobarakeh--2021|Rahnama Mobarakeh et al. 2021]] ; [[#Silva--2021|Silva et al. 2021]] ) (Chapter 11). Besides integrating solar thermal panels and solar PV into buildings and other infrastructure, floating solar PV panels in, for example, hydropower dams ( [[#Ranjbaran--2019|Ranjbaran et al. 2019]] ; [[#Cagle--2020|Cagle et al. 2020]] ; [[#Haas--2020|Haas et al. 2020]] ; Lee et al. 2020; [[#Gonzalez%20Sanchez--2021|Gonzalez Sanchez et al. 2021]] ), and over canals (Lee et al. 2020; [[#McKuin--2021|McKuin et al. 2021]] ) could decouple renewable energy generation from land use while simultaneously reducing evaporation losses and potentially mitigating aquatic weed growth and climate change impacts on water body temperature and stratification ( [[#Cagle--2020|Cagle et al. 2020]] ; [[#Exley--2021|Exley et al. 2021]] ; [[#Gadzanku--2021|Gadzanku et al. 2021]] ; [[#Solomin--2021|Solomin et al. 2021]] ).

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=== 12.5.3 Consequences of Land Occupation: Biophysical and Socio-economic Risks, Impacts and Opportunities ===

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Land occupation associated with mitigation options can present challenges related to impacts and trade-offs, but can also provide opportunities and in different ways support the achievement of additional societal objectives, including adaptation to climate change. This section focuses on mitigation options that have significant risks, impacts and/or co-benefits with respect to land resources, food security and the environment. Bioenergy (with or without CCS), biochar and bio-based products require biomass feedstocks that can be obtained from purpose-grown crops, residues from conventional agriculture and forestry systems, or from biomass wastes, each with different implications for the land. Here we consider separately (i) ‘biomass-based systems’, including dedicated biomass crops (e.g., perennial grasses, short rotation woody crops) and biomass produced as a co-product of conventional agricultural production (e.g., maize stover), and (ii) ‘afforestation/reforestation’, including forests established for ecological restoration and plantations grown for forest products and agroforestry, where biomass may also be a co-product. We then discuss impacts and opportunities common to both systems, before considering impacts and opportunities associated with non-land-based mitigation options that nevertheless occupy land.

Mitigation options that are based on the use of biomass, that is, bioenergy/BECCS, biochar, wood buildings, and other bio-based products, can have different positive and negative effects depending on the character of the mitigation option, the land use, the biomass conversion process, how the bio-based products are used and what other product they substitute ( [[#Leskinen--2018|Leskinen et al. 2018]] ; [[#Howard--2021|Howard et al. 2021]] ; [[#Myllyviita--2021|Myllyviita et al. 2021]] ). The impacts of the same mitigation option can therefore vary significantly and the outcome in addition depends on previous land/biomass use ( [[#Cowie--2021|Cowie et al. 2021]] ). As biomass-based systems commonly produce multiple food, material and energy products, it is difficult to disentangle impacts associated with individual bio-based products ( [[#Ahlgren--2015|Ahlgren et al. 2015]] ; [[#Djomo--2017|Djomo et al. 2017]] ; [[#Obydenkova--2021|Obydenkova et al. 2021]] ). As for other mitigation options, governance has a critical influence on outcome, but larger scale and higher expansion rate generally translates into higher risk for negative outcomes such as competition for scarce land, freshwater and phosphorous resources, displacement of natural ecosystems, and diminishing capacity of agroecosystems to support biodiversity and essential ecosystem services, especially if produced without sustainable land management and in inappropriate contexts ( [[#Popp--2017|Popp et al. 2017]] ; [[#Dooley--2018|Dooley and Kartha 2018]] ; [[#Hasegawa--2018|Hasegawa et al. 2018]] ; [[#Heck--2018|Heck et al. 2018]] ; [[#Humpenöder--2018|Humpenöder et al. 2018]] ; [[#Fujimori--2019|Fujimori et al. 2019]] ; [[#Hurlbert--2019|Hurlbert et al. 2019]] ; [[#IPBES--2019|IPBES 2019]] ; [[#Smith--2019b|Smith et al. 2019b]] ; [[#Drews--2020|Drews et al. 2020]] ; [[#Hasegawa--2020|Hasegawa et al. 2020]] ; [[#Schulze--2020|Schulze et al. 2020]] ; Stenzel et al. 2021) ( ''medium evidence'' , ''h'' ''igh agreement'' ).

Removal of crop and forestry residues can cause land degradation through soil erosion and decline in nutrients and soil organic matter ( [[#Cherubin--2018|Cherubin et al. 2018]] ) ( ''robust evidence'' , ''high agreement'' ). These risks can be reduced by retaining a proportion of the residues to protect the soil surface from erosion and moisture loss and maintain or increase soil organic matter ( [[IPCC:Wg3:Chapter:Chapter-7#7.4.3.6|Section 7.4.3.6]] ); incorporating a perennial groundcover into annual cropping systems ( [[#Moore--2019|Moore et al. 2019]] ); and by replacing nutrients removed, such as by applying ash from bioenergy combustion plants ( [[#Kludze--2013|Kludze et al. 2013]] ; [[#Harris--2015|Harris et al. 2015]] ; [[#Warren%20Raffa--2015|Warren Raffa et al. 2015]] ; [[#de%20Jong--2017|de Jong et al. 2017]] ) while safeguarding against contamination risks ( [[#Pettersson--2020|Pettersson et al. 2020]] ) ( ''medium evidence'' , ''high agreement'' ). Besides topography, soil, and climate conditions, sustainable residue removal rates also depend on the fate of extracted biomass. For example, to maintain the same level of soil organic carbon, the harvest of straw, if used for combustion (which would return no carbon to fields), was estimated to be only 26% of the rate that could be extracted if used for anaerobic digestion involving return of recalcitrant carbon to fields ( [[#Hansen--2020|Hansen et al. 2020]] ). Similarly, biomass pyrolysis produces biochar which can be returned to soils to counteract carbon losses associated with biomass extraction ( [[#Joseph--2021|Joseph et al. 2021]] ; [[#Lehmann--2021|Lehmann et al. 2021]] ).

Expansion of biomass crops, especially monocultures of exotic species, can pose risks to natural ecosystems and biodiversity through introduction of invasive species and land use change, also impacting the mitigation value ( ''robust evidence'' , ''high agreement'' ) ( [[#Liu--2014|Liu et al. 2014]] ; [[#El%20Akkari--2018|El Akkari et al. 2018]] ). Cultivation of conventional oil, sugar, and starch crops tends to have larger negative impact than lignocellulosic crops ( [[#Núñez-Regueiro--2020|Núñez-Regueiro et al. 2020]] ). Social and environmental outcomes can be enhanced through integration of suitable plants (such as perennial grasses and short rotation woody crops) into agricultural landscapes (within crop rotations or through strategic localisation, for example as contour belts, along fencelines and riparian buffers). Such integrated systems can provide shelter for livestock, retention of nutrients and sediment, erosion control, pollination, pest and disease control, and flood regulation ( ''robust evidence'' , ''high agreement'' ) ( [[#Berndes--2008|Berndes et al. 2008]] ; [[#Christen--2013|Christen and Dalgaard 2013]] ; [[#Asbjornsen--2014|Asbjornsen et al. 2014]] ; [[#Holland--2015|Holland et al. 2015]] ; [[#Ssegane--2015|Ssegane et al. 2015]] ; [[#Dauber--2016|Dauber and Miyake 2016]] ; [[#Milner--2016|Milner et al. 2016]] ; [[#Ssegane--2016|Ssegane and Negri 2016]] ; [[#Styles--2016|Styles et al. 2016]] ; [[#Zheng--2016|Zheng et al. 2016]] ; [[#Ferrarini--2017|Ferrarini et al. 2017]] ; Crews et al. 2018; [[#Henry--2018a|Henry et al. 2018a]] ; [[#Zalesny--2019|Zalesny et al. 2019]] ; [[#Osorio--2019|Osorio et al. 2019]] ; [[#Englund--2020b|Englund et al. 2020b]] ; [[#Englund--2021|Englund et al. 2021]] ) (Figure 12.8, Box 12.3, and Cross-Working Group Box 3 in this chapter). Many of the land use practices described above align with agroecology principles (AR6 WGII [[IPCC:Wg3:Chapter:Chapter-5#5.1|Section 5.1]] 4, AR6 WGII Box 5.11 and AR6 WGII Cross-Chapter Box NATURAL) and can simultaneously contribute to climate change mitigation, climate change adaptation and reduced risk of land degradation ( [[#IPCC--2019a|IPCC 2019a]] ) ( ''robust evidence'' , ''h'' ''igh agreement'' ).

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[[File:21fda9e515dbacbb32cd74644e31fea3 IPCC_AR6_WGIII_Figure_12_8.png]]

'''Figure 12.8 | Overview of opportunities related to selected land-based climate change miti''' '''gation options.'''

When A/R activities comprise the establishment of natural forests, the risk to land is primarily associated with potential displacement of previous land use to new locations, which could indirectly cause land-use change including deforestation (Sections 7.4.2 and 7.6.2.4). A/R (including agroforestry) aimed at providing timber, fibre, biomass, non-timber resources and other ecosystem services can provide renewable resources to society and long-term livelihoods for communities. Forest management and harvesting regimes around the world will adjust in different ways as society seeks to meet climate goals. The outcome depends on forest type, climate, forest ownership and the character and product portfolio of the associated forest industry ( [[#Lauri--2019|Lauri et al. 2019]] ; [[#Favero--2020|Favero et al. 2020]] ). How forest carbon stocks, biodiversity, hydrology, and so on are affected by changes in forest management and harvesting in turn depends on both management practices and the characteristics of the forest ecosystems ( [[#Eales--2018|Eales et al. 2018]] ; [[#Griscom--2018|Griscom et al. 2018]] ; [[#Kondo--2018|Kondo et al. 2018]] ; [[#Nieminen--2018|Nieminen et al. 2018]] ; [[#Thom--2018|Thom et al. 2018]] ; [[#Runting--2019|Runting et al. 2019]] ; [[#Tharammal--2019|Tharammal et al. 2019]] ) ( ''robust evidence'' , ''medium agreement'' ). As described above, the GHG savings achieved from producing and using bio-based products will in addition depend on the character of existing societal systems, including technical infrastructure and markets, as this determines the product substitution patterns.

Environmental and socio-economic co-benefits are enhanced when ecological restoration principles are applied ( [[#Gann--2019|Gann et al. 2019]] ) along with effective planning at landscape level and strong governance (Morgan et al., 2020). For example, restoration of natural vegetation and establishing plantations on degraded land enable organic matter to accumulate in the soil and have potential to deliver significant co-benefits for biodiversity, land resource condition and livelihoods (Box 12.3 and Cross-Working Group Box 3 in this chapter). Tree planting and agroforestry on cleared land can deliver biodiversity benefits ( [[#Seddon--2009|Seddon et al. 2009]] ; [[#Kavanagh--2012|Kavanagh and Stanton 2012]] ; [[#Law--2014|Law et al. 2014]] ), with biodiversity outcomes influenced by block size, configuration and species mix ( [[#Cunningham--2015|Cunningham et al. 2015]] ; [[#Paul--2016|Paul et al. 2016]] ) ( ''robust evidence'' , ''h'' ''igh agreement'' ).

Biomass-based systems and A/R can contribute to addressing land degradation through land rehabilitation or restoration (Box 12.3). Land-based mitigation options that produce biomass for bioenergy/BECCS or biochar through land ''rehabilitation'' rather than land ''restoration'' imply a trade-off between production / carbon sequestration and biodiversity outcomes ( [[#Hua--2016|Hua et al. 2016]] ; [[#Cowie--2018|Cowie et al. 2018]] ). Restoration, seeking to establish native vegetation with the aim to maximise ecosystem integrity, landscape connectivity, and conservation of on-ground carbon stock, will have higher biodiversity benefits than rehabilitation measures ( [[#Lin--2013|Lin et al. 2013]] ). However, sequestration rate declines as forests mature, and the sequestered carbon is vulnerable to loss through disturbance such as wildfire, so there is a higher risk of reversal of the mitigation benefit compared with use of biomass for substitution of fossil fuels and GHG-intensive building materials ( [[#Russell--2017|Russell and Kumar 2017]] ; [[#Dugan--2018|Dugan et al. 2018]] ; [[#Anderegg--2020|Anderegg et al. 2020]] ). Trade-offs between different ecosystem services, and between societal objectives including climate change mitigation and adaptation, can be managed through integrated landscape approaches that aim to create a mosaic of land uses, including conservation, agriculture, forestry and settlements ( [[#Freeman--2015|Freeman et al. 2015]] ; [[#Nielsen--2016|Nielsen 2016]] ; [[#Reed--2016|Reed et al. 2016]] ; [[#Sayer--2017|Sayer et al. 2017]] ) where each is sited with consideration of land potential and socio-economic objectives and context ( [[#Cowie--2018|Cowie et al. 2018]] ) ( ''limited evidence'' , ''h'' ''igh agreement'' ) ''.''

Impacts of biomass production and A/R on the hydrological cycle and water availability and quality depend on scale, location, previous land use/cover and type of biomass production system. For example, extraction of logging residues in forests managed for timber production has little effect on hydrological flows, while land-use change to establish dedicated biomass production can have a significant effect ( [[#Teter--2018|Teter et al. 2018]] ; [[#Drews--2020|Drews et al. 2020]] ). Deployment of A/R can affect temperature, albedo and precipitation locally and regionally, and can mitigate or enhance the effects of climate change in the affected areas ( [[#Stenzel--2021b|Stenzel et al. 2021b]] ) ( [[IPCC:Wg3:Chapter:Chapter-7#7.2.4|Section 7.2.4]] ). A/R activities can increase evapotranspiration, impacting groundwater and downstream water availability, but can also result in increased infiltration to groundwater and improved water quality ( [[#Farley--2005|Farley et al. 2005]] ; [[#Zhang--2016|Zhang et al. 2016]] ; [[#Zhang--2017|Zhang et al. 2017]] ; [[#Lu--2018|Lu et al. 2018]] ) and can be beneficial where historical clearing has caused soil salinisation and stream salinity ( [[#Farrington--1996|Farrington and Salama 1996]] ; [[#Marcar--2016|Marcar 2016]] ). There is ''limited evidence'' that very large-scale land-use or vegetation cover changes can alter regional climate and precipitation patterns, for example downwind precipitation depends on upwind evapotranspiration from forests and other vegetation ( [[#Keys--2016|Keys et al. 2016]] ; [[#Ellison--2017|Ellison et al. 2017]] ; [[#van%20der%20Ent--2017|van der Ent and Tuinenburg 2017]] ).

Another example of beneficial effects includes perennial grasses and woody crops planted to intercept runoff and subsurface lateral flow, reducing nitrate entering groundwater and surface waterbodies ( [[#Femeena--2018|Femeena et al. 2018]] ; [[#Woodbury--2018|Woodbury et al. 2018]] ; [[#Griffiths--2019|Griffiths et al. 2019]] ). In India, [[#Garg--2011|Garg et al. (2011)]] found desirable effects as a result of planting Jatropha on wastelands previously used for grazing (which could continue in the Jatropha plantations): soil evaporation was reduced, as a larger share of the rainfall was channelled to plant transpiration and groundwater recharge, and less runoff resulted in reduced soil erosion and improved downstream water conditions. Thus, adverse effects can be reduced and synergies achieved when plantings are sited carefully, with consideration of potential hydrological impacts ( [[#Davis--2013|Davis et al. 2013]] ).

Several biomass conversion technologies can generate co-benefits for land and water. Anaerobic digestion of organic wastes (e.g., food waste, manure) produces a nutrient-rich digestate and biogas that can be utilised for heating and cooking or upgraded for use in electricity generation, industrial processes, or as transportation fuel (Chapter 6) ( [[#Parsaee--2019|Parsaee et al. 2019]] ; [[#Hamelin--2021|Hamelin et al. 2021]] ). The digestate is a rich source of nitrogen, phosphorus and other plant nutrients, and its application to farmland returns exported nutrients as well as carbon ( [[#Cowie--2020b|Cowie 2020b]] ). Studies have identified potential risks, including manganese toxicity, copper and zinc contamination, and ammonia emissions, compared with application of undigested animal manure ( [[#Nkoa--2014|Nkoa 2014]] ). Although the anaerobic digestion process reduces pathogen risk compared with undigested manure feedstocks, it does not destroy all pathogens ( [[#Nag--2019|Nag et al. 2019]] ). Leakage of methane is a significant risk that needs to be managed, to ensure mitigation potential is achieved ( [[#Bruun--2014|Bruun et al. 2014]] ). Anaerobic digestion of wastewater, such as sugarcane vinasse, reduces methane emissions and pollution loading as well as producing biogas ( [[#Parsaee--2019|Parsaee et al. 2019]] ).

Biorefineries can convert biomass to food, feed and biomaterials along with bioenergy ( [[#Aristizábal‐Marulanda--2019|Aristizábal‐Marulanda and Cardona Alzate 2019]] ; [[#Schmidt--2019|Schmidt et al. 2019]] ). Biorefinery plants are commonly characterised by high process integration to achieve high resource use efficiency, minimise waste production and energy requirements, and maintain flexibility towards changing markets for raw materials and products ( [[#Schmidt--2019|Schmidt et al. 2019]] ). Emerging technologies can convert biomass that is indigestible for monogastric animals or humans (e.g., algae, grass, clover or alfalfa) into food and feed products. For example, lactic acid bacteria can facilitate the use of green plant biomass such as grasses and clover to produce a protein concentrate suitable for animal feed and other products for material or energy use ( [[#Lübeck--2019|Lübeck and Lübeck 2019]] ). Selection of crops suitable for co-production of protein feed along with biofuels and other bio-based products can significantly reduce the land conversion pressure by reducing the need to cultivate other crops (e.g., soybean) for animal feed ( [[#Bentsen--2017|Bentsen and Møller 2017]] ; [[#Solati--2018|Solati et al. 2018]] ). Thus, such solutions, using alternatives to high-input, high-emissions grain-based feed, can enable sustainable intensification of agricultural systems with reduced environmental impacts ( [[#Jørgensen--2016|Jørgensen and Lærke 2016]] ). The use of seaweed and algae as biorefinery feedstock can facilitate recirculation of nutrients from waters to agricultural land, thus reducing eutrophication while substituting purpose-grown feed ( [[#Thomas--2021|Thomas et al. 2021]] ).

Pyrolysis can convert organic wastes, including agricultural and forestry residues, food waste, manure, poultry litter and sewage sludge, into combustible gas and biochar, which can be used as a soil amendment ( [[#Joseph--2021|Joseph et al. 2021]] ; [[#Schmidt--2021|Schmidt et al. 2021]] ) (Chapter 7). Pyrolysis facilitates nutrient recovery from biomass residues, enabling return to farmland as biochar, noting, however, that a large fraction of nitrogen is lost during pyrolysis ( [[#Joseph--2021|Joseph et al. 2021]] ). Conversion to biochar aids the logistics of transport and land application of materials such as sewage sludge, by reducing mass and volume, improving flow properties, stability and uniformity, and decreasing odour. Pyrolysis is well suited for materials that may be contaminated with pathogens, microplastics, and per- and polyfluoroalkyl substances, such as abattoir and sewage wastes, removing these risks, and reduces availability of heavy metals in feedstock ( [[#Joseph--2021|Joseph et al. 2021]] ). Applying biochar to soil sequesters biochar-carbon for hundreds to thousands of years and can further increase soil carbon by reducing mineralisation of soil organic matter and newly added plant carbon ( [[#Singh--2012|Singh et al. 2012]] ; [[#Wang--2016a|Wang et al. 2016a]] ; Weng et al. 2017; [[#Lehmann--2021|Lehmann et al. 2021]] ). Biochars can improve a range of soil properties, but effects vary depending on biochar properties, which are determined by feedstock and production conditions ( [[#Singh--2012|Singh et al. 2012]] ; [[#Wang--2016a|Wang et al. 2016a]] ), and on the soil properties where biochar is applied ( [[#Razzaghi--2020|Razzaghi et al. 2020]] ). Biochars can increase nutrient availability, reduce leaching losses (Singh et al. 2010; [[#Haider--2017|Haider et al. 2017]] ) and enhance crop yields, particularly in infertile acidic soils ( [[#Jeffery--2017|Jeffery et al. 2017]] ), thus supporting food security under changing climate. Biochars can enhance infiltration and soil water-holding capacity, reducing runoff and leaching, increasing water retention in the landscape and improving drought tolerance and resilience to climate change ( [[#Quin--2014|Quin et al. 2014]] ; [[#Omondi--2016|Omondi et al. 2016]] ). (See [[IPCC:Wg3:Chapter:Chapter-7|Chapter 7]] for a review of biochar’s potential contribution to climate change mitigation.)

Both A/R and dedicated biomass production could have adverse impacts on food security and cause indirect land-use change if deployed in locations used for food production ( [[#IPCC--2019a|IPCC 2019a]] ). But the degree of impact associated with a certain mitigation option also depends on how deployment takes place and the rate and total scale of deployment. The highest increases in food insecurity due to deployment of land-based mitigation are expected to occur in sub-Saharan Africa and Asia ( [[#Hasegawa--2018|Hasegawa et al. 2018]] ). The land area that could be used for bioenergy or other land-based mitigation options with low to moderate risks to food security depends on patterns of socio-economic development, reaching limits between 1 and 4 million km 2 ( [[#Hurlbert--2019|Hurlbert et al. 2019]] ; [[#IPCC--2019a|IPCC 2019a]] ; Smith et al. 2019c).

The use of less productive, degraded/marginal lands has received attention as an option for biomass production and other land-based mitigation that can improve the productive and adaptive capacity of the lands ( [[#Liu--2017|Liu et al. 2017]] ; [[#Qin--2018|Qin et al. 2018]] ; [[#Dias--2021|Dias et al. 2021]] ; [[#Kreig--2021|Kreig et al. 2021]] ) ( [[IPCC:Wg3:Chapter:Chapter-7#7.4.4|Section 7.4.4]] and Cross-Working Group Box 3 in this chapter). The potential is however uncertain as biomass growth rates may be low, a variety of assessment approaches have been used, and the identification of degraded/marginal land as ‘available’ has been contested, as much low productivity land is used informally by impoverished communities, particularly for grazing, or may be economically infeasible or environmentally undesirable for development of energy crops ( ''medium evidence'' , ''low agreement'' ) ( [[#Baka--2013|Baka 2013]] ; [[#Fritz--2013|Fritz et al. 2013]] ; [[#Haberl--2013|Haberl et al. 2013]] ; [[#Baka--2014|Baka 2014]] ).

As many of the SDGs are closely linked to land use, the identification and promotion of mitigation options that rely on land uses described above can support a growing use of bio-based products while advancing several SDGs, such as SDG 2 (zero hunger), SDG 6 (clean water and sanitation), SDG 7 (affordable and clean energy) and SDG 15 (life on land) ( [[#Fritsche--2017|Fritsche et al. 2017]] ; IRP 2019; [[#Blair--2021|Blair et al. 2021]] ). Policies supporting the target of Land Degradation Neutrality (LDN) (SDG 15.3) encourage planning of measures to counteract loss of productive land due to unsustainable agricultural practices and land conversion, through sustainable land management and strategic restoration and rehabilitation of degraded land ( [[#Cowie--2018|Cowie et al. 2018]] ). LDN can thus be an incentive for land-based mitigation measures that build carbon in vegetation and soil, and can provide impetus for land-use planning to achieve multifunctional landscapes that integrate land-based mitigation with other land uses (Box 12.3). The application of sustainable land management practices that build soil carbon will enhance the productivity and resilience of crop and forestry systems, thereby enhancing biomass production ( [[#Henry--2018a|Henry et al. 2018a]] ). Non-bio-based mitigation options can enhance land-based mitigation: (i) enhanced weathering, that is, adding ground silicate rock to soil to take up atmospheric CO 2 through chemical weathering ( [[#12.3|Section 12.3]] ), could supply nutrients and alleviate soil acidity, thereby boosting productivity of biomass crops and A/R, particularly when combined with biochar application ( [[#Haque--2019|Haque et al. 2019]] ; [[#De%20Oliveira%20Garcia--2020|De Oliveira Garcia et al. 2020]] ; [[#Buss--2021|Buss et al. 2021]] ); and (ii) land rehabilitation and enhanced landscape diversity through production of biomass crops could simultaneously contribute to climate change mitigation, climate change adaptation, addressing land degradation, increasing biodiversity and improving food security in the longer term ( [[#Mackey--2020|Mackey et al. 2020]] ) (Chapter 7).

The land requirement and impacts (including visual and noise impacts) of onshore wind turbines depend on the size and type of installation, and location ( [[#Ioannidis--2020|Ioannidis and Koutsoyiannis 2020]] ). Wind power and agriculture can coexist in beneficial ways and wind power production on agriculture land is well established ( [[#Fritsche--2017|Fritsche et al. 2017]] ; [[#Miller--2018a|Miller and Keith 2018a]] ). Spatial planning and local stakeholder engagement can reduce opposition due to visual landscape impacts and noise ( [[#Frolova--2019|Frolova et al. 2019]] ; [[#Hevia-Koch--2019|Hevia-Koch and Ladenburg 2019]] ). Repowering, that is, replacing with higher capacity wind turbines, can mitigate additional land requirement associated with deployment towards higher share of wind in power systems ( [[#Pryor--2020|Pryor et al. 2020]] ).

Mortality and disturbance risks to birds, bats and insects are major ecological concerns associated with wind farms ( [[#Thaxter--2017|Thaxter et al. 2017]] ; [[#Cook--2018|Cook et al. 2018]] ; [[#Heuck--2019|Heuck et al. 2019]] ; [[#Coppes--2020|Coppes et al. 2020]] ; [[#Choi--2020|Choi et al. 2020]] ; [[#Fernández-Bellon--2020|Fernández-Bellon 2020]] ; [[#Marques--2020|Marques et al. 2020]] ; [[#Voigt--2021|Voigt 2021]] ). Careful siting is critical ( [[#May--2021|May et al. 2021]] ), while painting blades to increase the visibility can also reduce mortality due to collision ( [[#May--2020|May et al. 2020]] ). Theoretical studies have suggested that wind turbines could lead to warmer night temperatures due to atmospheric mixing ( [[#Keith--2004|Keith et al. 2004]] ), later confirmed through observation ( [[#Zhou--2013|Zhou et al. 2013]] ), although [[#Vautard--2014|Vautard et al. (2014)]] found limited impact at scales consistent with climate policies. More recent studies report mixed results: indications that the warming effect could be substantial with widespread deployment ( [[#Miller--2018b|Miller and Keith 2018b]] ) and conversely limited impacts on regional climate at 20% of US electricity from wind. ( [[#Pryor--2020|Pryor et al. 2020]] ).

As for wind power, land impacts of solar power depend on the location, size and type of installation ( [[#Ioannidis--2020|Ioannidis and Koutsoyiannis 2020]] ). Establishment of large-scale solar farms could have positive or negative environmental effects at the site of deployment, depending on the location. Solar PV and CSP power installations can lock away land areas, displacing other uses ( [[#Mohan--2017|Mohan 2017]] ). Solar PV can be deployed in ways that enhance agriculture: for example, [[#Hassanpour%20Adeh--2018|Hassanpour Adeh et al. (2018)]] found that biomass production and water use efficiency of pasture increased under elevated solar panels. PV systems under development may achieve significant power generation without diminishing agricultural output ( [[#Miskin--2019|Miskin et al. 2019]] ). Global mapping of solar panel efficiency showed that croplands, grasslands and wetlands are located in regions with the greatest solar PV potential ( [[#Adeh--2019|Adeh et al. 2019]] ). Dual-use agrivoltaic systems are being developed that overcome previously recognised negative impact on crop growth, mainly due to shadows ( [[#Marrou--2013a|Marrou et al. 2013a]] ; [[#Marrou--2013b|Marrou et al. 2013b]] ; [[#Armstrong--2016|Armstrong et al. 2016]] ), thus facilitating synergistic co-location of solar photovoltaic power and cropping ( [[#Adeh--2019|Adeh et al. 2019]] ; [[#Miskin--2019|Miskin et al. 2019]] ). Assessment of the potential for optimising deployment of solar PV and energy crops on abandoned cropland areas produced an estimate of the technical potential for optimal combination at 125 EJ per year ( [[#Leirpoll--2021|Leirpoll et al. 2021]] ).

Deserts can be well suited for solar PV and CSP farms, especially at low latitudes where global horizontal irradiance is high, as there is lower competition for land and land carbon loss is minimal, although remote locations may pose challenges for power distribution ( [[#Xu--2016|Xu et al. 2016]] ). Solar arrays can reduce the albedo, particularly in desert landscapes, which can lead to local temperature increases and regional impacts on wind patterns ( [[#Millstein--2011|Millstein and Menon 2011]] ). Modelling studies suggest that large-scale wind and solar farms, for example in the Sahara ( [[#Li--2018|Li et al. 2018]] ), could increase rainfall through reduced albedo and increased surface roughness, stimulating vegetation growth and further increasing regional rainfall ( [[#Li--2018|Li et al. 2018]] ) ( ''limited evidence'' ). Besides impacts at the site of deployment, wind and solar power affect land through mining of critical minerals required by these technologies ( [[#Viebahn--2015|Viebahn et al. 2015]] ; [[#McLellan--2016|McLellan et al. 2016]] ; [[#Carrara--2020|Carrara et al. 2020]] ).

Nuclear power has land impacts and risks associated with mining operations ( [[#Falck--2015|Falck 2015]] ; [[#Winde--2017|Winde et al. 2017]] ; [[#Srivastava--2020|Srivastava et al. 2020]] ) and disposal of spent fuel ( [[#IAEA--2006a|IAEA 2006a]] ; [[#Ewing--2016|Ewing et al. 2016]] ; [[#Bruno--2020|Bruno et al. 2020]] ), but the land occupation is small compared to many other mitigation options. Substantial volumes of water are required for cooling ( [[#Liao--2016|Liao et al. 2016]] ), as for all thermal power plants, but most of this water is returned to rivers and other water bodies after use (Sesma Martín and Rubio-Varas 2017). Negative impacts on aquatic systems can occur due to chemical and thermal pollution loading ( [[#Fricko--2016|Fricko et al. 2016]] ; [[#Raptis--2016|Raptis et al. 2016]] ; [[#Bonansea--2020|Bonansea et al. 2020]] ). The major risk to land from nuclear power is that a nuclear accident leads to radioactive contamination. An extreme example, the 1986 Chernobyl accident in Ukraine, resulted in radioactive contamination across Europe. Most of the fallout concentrated in Belarus, Ukraine and Russia, where some 125,000 km 2 of land (more than a third of which was in agricultural use) was contaminated. About 350,000 people were relocated away from these areas ( [[#IAEA--2006b|IAEA 2006b]] ; [[#Sovacool--2008|Sovacool 2008]] ). About 116,000 people were permanently evacuated from the 4200 km Chernobyl exclusion zone ( [[#IAEA--2006a|IAEA 2006a]] ). New reactor designs with passive and enhanced safety systems reduce the risk of such accidents significantly ( [[IPCC:Wg3:Chapter:Chapter-6#6.4.2.4|Section 6.4.2.4]] ). An example of alternatives to land reclamation for productive purposes, a national biosphere reserve has been established around Chernobyl to conserve, enhance and manage carbon stocks and biodiversity ( [[#Deryabina--2015|Deryabina et al. 2015]] ; [[#Ewing--2016|Ewing et al. 2016]] ), although invertebrate and plant populations are affected ( [[#Mousseau--2014|Mousseau and Møller 2014]] ; [[#Mousseau--2020|Mousseau and Møller 2020]] ).

Reservoir hydropower projects submerge areas as dams are established for water storage. Hydropower can be associated with significant and highly varying land occupation and carbon footprint ( [[#Poff--2016|Poff and Schmidt 2016]] ; [[#Scherer--2016a|Scherer and Pfister 2016a]] ; [[#dos%20Santos--2017|dos Santos et al. 2017]] ; [[#Ocko--2019|Ocko and Hamburg 2019]] ). The flooding of land causes CH 4 emissions due to the anaerobic decomposition of submerged vegetation and there is also a loss of carbon sequestration due to mortality of submerged vegetation. The size of GHG emissions depends on the amount of vegetation submerged. The carbon in accumulated sediments in reservoirs may be released to the atmosphere as CO 2 and CH 4 upon decommissioning of dams, and while uncertain, estimates indicate that these emissions can make up a significant part of the cumulative GHG emissions of hydroelectric power plants ( [[#Moran--2018|Moran et al. 2018]] ; [[#Almeida--2019|Almeida et al. 2019]] ; [[#Ocko--2019|Ocko and Hamburg 2019]] ). Positive radiative forcing due to lower albedo of hydropower reservoirs compared to surrounding landscapes can reduce mitigation contribution significantly ( [[#Wohlfahrt--2021|Wohlfahrt et al. 2021]] ).

Hydropower can have high water usage due to evaporation from dams ( [[#Scherer--2016b|Scherer and Pfister 2016b]] ). Hydropower projects may impact aquatic ecology and biodiversity, necessitate the relocation of local communities living within or near the reservoir or construction sites, and affect downstream communities (in positive or negative ways) ( [[#Moran--2018|Moran et al. 2018]] ; [[#Barbarossa--2020|Barbarossa et al. 2020]] ). Displacement as well as resettlement schemes can have both socio-economic and environmental consequences including those associated with establishment of new agricultural land ( [[#Ahsan--2016|Ahsan and Ahmad 2016]] ; [[#Nguyen--2017|Nguyen et al. 2017]] ). Dam construction may also stimulate migration into the affected region, which can lead to deforestation and other negative impacts ( [[#Chen--2015|]] [[#Chen--2015|Chen et al. 2015]] ). Impacts can be mitigated through basin-scale dam planning that considers GHG emissions along with social and ecological effects ( [[#Almeida--2019|Almeida et al. 2019]] ). Land occupation is minimal for run-of-river hydropower installations, but without storage they have no resilience to drought and installations inhibit dispersal and migration of organisms ( [[#Lange--2018|Lange et al. 2018]] ). Reservoir hydropower schemes can regulate water flows and reduce flood damage to agricultural production ( [[#Amjath-Babu--2019|Amjath-Babu et al. 2019]] ). On the other hand, severe flooding due to failure of hydropower dams has caused fatalities, damage to infrastructure and loss of productive land ( [[#Farrington--1996|Farrington and Salama 1996]] ; [[#Farley--2005|Farley et al. 2005]] ; [[#Zhang--2016|Zhang et al. 2016]] ; [[#Marcar--2016|Marcar 2016]] ; [[#Zhang--2017|Zhang et al. 2017]] ; [[#Kalinina--2018|Kalinina et al. 2018]] ; [[#Lu--2018|Lu et al. 2018]] ).

<div id="12.5.4" class="h2-container"></div>

<span id="governance-of-land-related-impacts-of-mitigation-options"></span>
=== 12.5.4 Governance of Land-related Impacts of Mitigation Options ===

<div id="h2-22-siblings" class="h2-siblings"></div>

The land sector (Chapter 7) contributes to mitigation via emissions reduction and enhancement of land carbon sinks, and by providing biomass for mitigation in other sectors. Key challenges for governance of land-based mitigation include social and environmental safeguards ( [[#Duchelle--2017|Duchelle et al. 2017]] ; [[#Sills--2017|Sills et al. 2017]] ; [[#Larson--2018|Larson et al. 2018]] ); insufficient financing ( [[#Turnhout--2017|Turnhout et al. 2017]] ); capturing co-benefits; ensuring additionality; addressing non-permanence of carbon sequestration; monitoring, reporting, and verification (MRV) of emissions reduction and carbon dioxide removals; and avoiding leakage or spillover effects. Governance approaches to addressing these challenges are discussed in [[IPCC:Wg3:Chapter:Chapter-7#7.6|Section 7.6]] , and include MRV systems and integrity criteria for project-level emissions trading; payments for ecosystem services; land-use planning and land zoning; certification schemes, standards and codes of practice.

With respect to renewable energy options that occupy land, the focus of governance has been directed to technological adoption and public acceptance ( [[#Sequeira--2018|Sequeira and Santos 2018]] ), rather than land use. Recent work has found that spatial processes shape the emerging energy transition, creating zones of friction between global investors, national and local governments, and civil society ( [[#Jepson--2017|Jepson and Caldas 2017]] ; [[#McEwan--2017|McEwan 2017]] ). For example, [[#Yenneti--2016|Yenneti et al. (2016)]] have argued that hydropower and ground-based solar parks in India, which have involved enclosure of lands designated as degraded, displacing pastoral use by vulnerable communities, have constituted forms of spatial injustice. Hydropower leads to dam-induced displacement, and though this can be addressed through compensation mechanisms, governance is complicated by a lack of transparency in resettlement data ( [[#Kirchherr--2016|Kirchherr et al. 2016]] ; [[#Kirchherr--2019|Kirchherr et al. 2019]] ). Renewable energy production is resulting in new land conflict frontiers where degraded land is framed as having mitigation value such as for palm oil production and wind power in Mexico ( [[#Backhouse--2020|Backhouse and Lehmann 2020]] ); land use conflict as well as impacts on wildlife from large-scale solar installations have also emerged in the southwestern United States ( [[#Mulvaney--2017|Mulvaney 2017]] ). The renewable energy transition also involves the extraction of critical minerals used in renewable energy technologies, such as lithium and cobalt. Governance challenges include the lack of transparent greenhouse gas accounting for mining activities ( [[#Lee--2020a|Lee et al. 2020a]] ), and threats to biodiversity from land disturbance, which require strategic planning to address ( [[#Sonter--2020a|Sonter et al. 2020a]] ). Strategic spatial planning is needed more generally to address trade-offs between using land for renewable energy and food: for example, agriculture can be co-located with solar photovoltaics ( [[#Barron-Gafford--2019|Barron-Gafford et al. 2019]] ) or wind power ( [[#Miller--2018a|Miller and Keith 2018a]] ). Integrative spatial planning can integrate renewable energy with not just agriculture, but mobility and housing ( [[#Hurlbert--2019|Hurlbert et al. 2019]] ). Integrated planning is needed to avoid scalar pitfalls, and local and regional contextualised governance solutions need to be sited within a planetary frame of reference ( [[#Biermann--2016|Biermann et al. 2016]] ). Greater planning and coordination are also needed to ensure co-benefits from land-based mitigation (Box 12.3) as well as from CDR and efforts to reduce food systems emissions.

In emerging domains for governance such as land-based mitigation, global institutions, private sector networks and civil society organisations are playing key roles in terms of norm-setting. The shared languages and theoretical frameworks, or cognitive linkages ( [[#Pattberg--2018|Pattberg et al. 2018]] ), that arise with polycentric governance can not only be helpful in creating expectations and establishing benchmarks for (in)appropriate practices where enforceable ‘hard law’ is missing ( [[#Karlsson-Vinkhuyzen--2018|Karlsson-Vinkhuyzen et al. 2018]] ; [[#Gajevic%20Sayegh--2020|Gajevic Sayegh 2020]] ), they can also form the basis of voluntary guidelines or niche markets (Box 12.3) However, the ability to apply participatory processes for developing voluntary guidelines and other participatory norm-setting endeavours varies from place to place. Social and cultural norms shape the ability of women, youth, and different ethnic groups to participate in governance fora, such as those around agroecological transformation ( [[#Anderson--2019|Anderson et al. 2019]] ). Furthermore, establishing new norms alone does not solve structural challenges such as lack of access to food, nor does it confront power imbalances, or provide mechanisms to deal with uncooperative actors ( [[#Morrison--2019|Morrison et al. 2019]] ).

<div id="Box 12.3 | Land Degradation Neutrality as a Framework to Manage Trade-offs in Land-b" class="h2-container"></div>

<span id="box-12.3-land-degradation-neutrality-as-a-framework-to-manage-trade-offs-in-land-b-ased-mitigation"></span>
=== Box 12.3 | Land Degradation Neutrality as a Framework to Manage Trade-offs in Land-based Mitigation ===

<div id="h2-23-siblings" class="h2-siblings"></div>

The United Nations Convention to Combat Desertification (UNCCD) introduced the concept of Land Degradation Neutrality (LDN), defined as ‘a state whereby the amount and quality of land resources necessary to support ecosystem functions and services and enhance food security remain stable or increase within specified temporal and spatial scales and ecosystems’ (UNCCD 2015), and it has been adopted as a target of SDG 15 (life on land). At December 2020, 124 (mostly developing) countries had committed to pursue voluntary LDN targets.

The goal of LDN is to maintain or enhance land-based natural capital, and its associated ecosystem services, such as provision of food and regulation of water and climate, while enhancing the resilience of the communities that depend on the land. LDN encourages a dual-pronged approach promoting sustainable land management (SLM) to avoid or reduce land degradation, combined with strategic effort in land restoration and rehabilitation to reverse degradation on degraded lands and thereby deliver the target of ‘no net loss’ of productive land ( [[#Orr--2017|Orr et al. 2017]] ).

In the context of LDN, land restoration refers to actions undertaken with the aim of reinstating ecosystem functionality, whereas land rehabilitation refers to actions undertaken with a goal of provision of goods and services ( [[#Cowie--2018|Cowie et al. 2018]] ). Restoration interventions can include destocking to encourage regeneration of native vegetation; shelter belts of local species established from seed or seedlings, strategically located to provide wildlife corridors and link habitat; and rewetting drained peatland. ‘Farmer-managed natural regeneration’ is a low-cost restoration approach in which regeneration of tree stumps and roots is encouraged, stabilising soil and

enhancing soil nutrients and organic matter levels ( [[#Chomba--2020|Chomba et al. 2020]] ; [[#Lohbeck--2020|Lohbeck et al. 2020]] ). Rehabilitation actions include establishment of energy crops, or afforestation with fast-growing exotic trees to sequester carbon or produce timber. Application of biochar can facilitate rehabilitation by enhancing nutrient retention and water-holding capacity, and stimulating microbial activity ( [[#Cowie--2020a|Cowie 2020a]] ).

SLM, rehabilitation and restoration activities undertaken towards national LDN targets have potential to deliver substantial CDR through carbon sequestration in vegetation and soil. In addition, biomass production, for bioenergy or biochar, could be an economically viable land use option for reversing degradation, through rehabilitation. Alternatively, a focus on ecological restoration ( [[#Gann--2019|Gann et al. 2019]] ) as the strategy for reversing degradation will deliver greater biodiversity benefits.

<div id="_idContainer009xa" class="Boxes_Blue-Boxes_•-Box-body"></div>

[[File:551abe74d7291c613c1b4db2b230cb81 IPCC_AR6_WGIII_Box_12_3_Figure_1.png]]

'''Box 12.3, Figure 1 | Schematic illustrating the elements of the Land Degradation Neutrality conceptual framework.''' Source: [[#Cowie--2018|Cowie et al. (2018)]] . Used with permission.

Achieving neutrality requires estimating the likely impacts of land-use and land-management decisions, to determine the area of land, of each land type, that is likely to be degraded ( [[#Orr--2017|Orr et al. 2017]] ). This information is used to plan interventions to reverse degradation on an equal area of the same land type. Therefore, pursuit of LDN requires concerted and coordinated efforts to integrate LDN objectives into land-use planning and land management, underpinned by sound understanding of the human–environment system and effective governance mechanisms.

Countries are advised to apply a landscape-scale approach for planning LDN interventions, in which land uses are matched to land potential, and resilience of current and proposed land uses is considered, to ensure that improvement in land condition is likely to be maintained ( [[#Cowie--2020a|Cowie 2020a]] ). A participatory approach that enables effective representation of all stakeholders is encouraged, to facilitate equitable outcomes from planning decisions, recognising that decisions on LDN interventions are likely to involve trade-offs between various environmental and socio-economic objectives ( [[#Schulze--2021|Schulze et al. 2021]] ).

Planning and implementation of LDN programmes provides a framework in which locally-adapted land-based mitigation options can be integrated with use of land for production, conservation and settlements, in multifunctional landscapes where trade-offs are recognised and managed, and synergistic opportunities are sought. LDN is thus a vehicle to focus collaboration in pursuit of the multiple land-based objectives of the multilateral environmental agreements and the SDGs.

Table 12.10 collates risks, impacts and opportunities associated with different mitigation options that occupy land.

'''Table 12.10 | Summary of impacts, risks and co-benefits associated with land occupation by mitigation options considered i''' '''n Section 12''' '''.''' '''5.'''

{| class="wikitable"
|-
! Mitigation option

! Impacts and risks

! Opportunities for co-benefits

|-
| colspan="3"| '''Non-bio-based options that may displace food production'''

|-
| '''Solar farms'''

| Land use competition; loss of soil carbon; heat island effect (scale dependent) (Sections 12.5.3 and 12.5.4)

| Target areas unsuitable for agriculture such as deserts ( [[#12.5.3|Section 12.5.3]] )

|-
| '''Hydropower (dams)'''

| Land use competition; displacement of natural ecosystems; CO 2 and CH 4 emissions (Sections 12.5.3 and 12.5.4)

| Water storage (including for irrigation) and regulation of water flows; pumped storage can store excess energy from other renewable generation sources ( [[#12.5.3|Section 12.5.3]] )

|-
| colspan="3"| '''Non-bio-based options that can (to a varying degree) be integrated with food production'''

|-
| '''Wind turbines'''

| May affect local/regional weather and climate (scale dependent); impacts on wildlife; visual impacts ( [[#12.5.3|Section 12.5.3]] )

| Design and siting informed by visual landscape impacts, relevant habitats, and flight trajectories of migratory birds ( [[#12.5.3|Section 12.5.3]] )

|-
| '''Solar panels'''

| Land use competition ( [[#12.5.3|Section 12.5.3]] )

| Integration with buildings and other infrastructure; integration with food production is being explored ( [[#12.5.2|Section 12.5.2]] )

|-
| '''Enhanced weathering (EW)'''

| Disturbance at sites of extraction; ineffective in low rainfall regions ( [[#12.3.1.2|Section 12.3.1.2]] )

| Increased crop yields and biomass production through nutrient supply and increasing pH of acid soils; synergies with biochar ( [[#12.5.3|Section 12.5.3]] )

|-
| colspan="3"| '''Bio-based options that may displace existing food production'''

|-
| '''Afforestation/reforestation (A/R)'''

| Land use competition, potentially leading to indirect land use change; reduced water availability; loss of biodiversity ( [[#12.5.3|Section 12.5.3]] )

| Strategic siting to minimise adverse impacts on hydrology, land use, biodiversity ( [[#12.5.3|Section 12.5.3]] )

|-
| '''Biomass crops'''

| Land use competition, potentially leading to indirect land-use change; reduced water availability; reduced soil fertility; loss of biodiversity ( [[#12.5.3|Section 12.5.3]] )

| Strategic siting to minimise adverse impacts/enhance beneficial effects on land use, landscape variability, biodiversity, soil organic matter, hydrology and water quality ( [[#12.5.3|Section 12.5.3]] )

|-
| colspan="3"| '''Bio-based options that can (to a varying degree) be combined with food production'''

|-
| '''Agroforestry'''

| Competition with adjacent crops and pastures reduces yields ( [[IPCC:Wg3:Chapter:Chapter-7#7.4.3.3|Section 7.4.3.3]] )

| Shelter for stock and crops, diversification, biomass production, increases soil organic matter and soil fertility; increased biodiversity and perennial vegetation enhance beneficial organisms; can reduce need for pesticides (Sections 7.4.3.3 and 12.5.3)

|-
| '''Soil carbon management in croplands and grasslands'''

| Increase in nitrous oxide emissions if fertiliser used to enhance crop production; reduced cereal production through increased crop legumes and pasture phases could lead to indirect land use change (Sections 7.4.3.1 and 7.4.3.6)

| Increasing soil organic matter improves soil health, increases crop and pasture yields and resilience to drought, can reduce fertiliser requirement, nutrient leaching and need for land use change ( [[IPCC:Wg3:Chapter:Chapter-7#7.4.3.1|Section 7.4.3.1]] )

|-
| '''Biochar addition to soil'''

| Land use competition if biochar is produced from purpose-grown biomass. Loss of forest carbon stock and impacts on biodiversity if biomass is harvested unsustainably. ( [[#12.5.3|Section 12.5.3]] )

| Facilitate beneficial use of organic residues, to return nutrients to farmland. Increased land productivity; increased carbon sequestration in vegetation and soil; increased nutrient-use efficiency, and reduced requirement for chemical fertiliser (Sections 7.4.3.2 and 12.5.3)

|-
| '''Harvest residue extraction and use for bioenergy, biochar and other bio-products'''

| Decline in soil organic matter and soil fertility ( [[#12.5.3|Section 12.5.3]] )

| Nutrients returned to soil e.g., as ash; reduced fuel load and wildfire risk (Sections 7.4.3.2 and 12.5.3)

|-
| '''Manure management (i.e., for biogas)'''

| Risk of fugitive emissions

Can contain pathogens (Sections 7.4.3.7 and 12.5.3)

| Biogas as renewable energy source, digestate as soil amendment ( [[#12.5.3|Section 12.5.3]] )

|-
| colspan="3"| '''Options that do not occupy land used for food production'''

|-
| '''Management of organic waste (food waste, biosolids, organic component of municipal solid waste)'''

| Can contain contaminants (heavy metals, persistent organic pollutants, pathogens) ( [[#12.5.3|Section 12.5.3]] )

| Processing using anaerobic digestion or pyrolysis produces renewable gas and soil amendment, enabling return of nutrients to farmland. (Note that some feedstock nitrogen is lost in pyrolysis) ( [[#12.5.3|Section 12.5.3]] )

|-
| '''A/R and biomass production on degraded non-forested land (e.g., abandoned agricultural land)'''

| High labour and material inputs can be needed; abandoned land can support informal grazing and have significant biodiversity value. Reduced water availability ( [[#12.5.3|Section 12.5.3]] )

| Application of biochar can re-establish nutrient cycling; bioenergy crops can add organic matter, restoring soil fertility, and can remove heavy metals, enabling food production (Sections 7.4.3.2 and 12.5.3)

|}

'''Cross-Working Group Box 3, Figure 1 | Left:''' High-input intensive agriculture, aiming for high yields of a few crop species, with large fields and no semi-natural habitats. '''Right:''' Agroecological agriculture, supplying a range of ecosystem services, relying on biodiversity and crop and animal diversity instead of external inputs, and integrating plant and animal production, with smaller fields and presence of semi-natural habitats. Source: Reprinted by permission from Springer Nature Customer Service Centre GmbH: Springer Nature, Nature Sustainability , Towards better representation of organic agriculture in life cycle assessment, Hayo M. G. van der Werf et al. © 2020.

<div id="Cross-Working Group Box 3 | Mitigation and Adaptation via the Bioeconomy" class="h2-container"></div>

<span id="cross-working-group-box-3-mitigation-and-adaptation-via-the-bioeconomy"></span>

=== Cross-Working Group Box 3 | Mitigation and Adaptation via the Bioeconomy ===

<div id="h2-24-siblings" class="h2-siblings"></div>

'''Authors:''' Henry Neufeldt (Denmark/Germany), Göran Berndes (Sweden), Almut Arneth (Germany), Rachel Bezner Kerr (the United States of America/Canada), Luisa F Cabeza (Spain), Donovan Campbell (Jamaica), Jofre Carnicer Cols (Spain), Annette Cowie (Australia), Vassilis Daioglou (Greece), Joanna House (United Kingdom), Adrian Leip (Italy/Germany), Francisco Meza (Chile), Michael Morecroft (United Kingdom), Gert-Jan Nabuurs (Netherlands), Camille Parmesan (United Kingdom/the United States of America), Julio C. Postigo (the United States of America/Peru), Marta G. Rivera-Ferre (Spain), Raphael Slade (United Kingdom), Maria Cristina Tirado von der Pahlen (the United States of America/Spain), Pramod K. Singh (India), Pete Smith (United Kingdom)

Summary statement

The growing demand for biomass offers both opportunities and challenges to mitigate and adapt to climate change and natural resource constraints ( ''high confidence'' ). Increased technology innovation, stakeholder integration and transparent governance structures and procedures at local to global scales are key to successful bioeconomy deployment maximising benefits and managing trade-offs ( ''hi'' ''gh confidence'' ).

Limited global land and biomass resources accompanied by growing demands for food, feed, fibre, and fuels, together with prospects for a paradigm shift towards phasing out fossil fuels, set the frame for potentially fierce competition for land [[#footnote-001|3]] and biomass to meet burgeoning demands, even as climate change increasingly limits natural resource potentials ( ''high confidence'' ).

Cross-Working Group Box 3

Sustainable agriculture and forestry, technology innovation in bio-based production within a circular economy, and international cooperation and governance of global trade in products to reflect and disincentivise their environmental and social externalities, can provide mitigation and adaptation via bioeconomy development that responds to the needs and perspectives of multiple stakeholders to achieve outcomes that maximise synergies while limiting trade-offs ( ''hi'' ''gh confidence'' ).

Background

There is ''high confidence'' that climate change, population growth and changes in per capita consumption will increase pressures on managed as well as natural and semi-natural ecosystems, exacerbating existing risks to livelihoods, biodiversity, human and ecosystem health, infrastructure, and food systems ( [[#Conijn--2018|Conijn et al. 2018]] ; [[#IPCC--2018|IPCC 2018]] ; [[#IPCC--2019a|IPCC 2019a]] ; [[#Lade--2020|Lade et al. 2020]] ). At the same time, many global mitigation scenarios presented in IPCC assessment reports rely on large GHG emissions reduction in the AFOLU sector and concurrent deployment of reforestation/afforestation and biomass use in a multitude of applications ( [[#Rogelj--2018|Rogelj et al. 2018]] ; Hanssen et al. 2020) (AR6 WGI Chapters 4 and 5, AR6 WGIII Chapters 3 and 7).

Given the finite availability of natural resources, there are invariably trade-offs that complicate land-based mitigation unless land productivity can be enhanced without undermining ecosystem services ( [[#Obersteiner--2016|Obersteiner et al. 2016]] ; [[#Campbell--2017|Campbell et al. 2017]] ; [[#Caron--2018|Caron et al. 2018]] ; [[#Conijn--2018|Conijn et al. 2018]] ; [[#Heck--2018|Heck et al. 2018]] ; Searchinger 2018a; Smith et al. 2019). Management intensities can often be adapted to local conditions with consideration of other functions and ecosystem services, but at a global scale the challenge remains to avoid further deforestation and degradation of intact ecosystems, in particular biodiversity-rich systems (AR6 WGII Cross-Chapter Box NATURAL), while meeting the growing demands. Further, increased land-use competition can affect food prices and impact food security and livelihoods ( [[#To--2015|To and Grafton 2015]] ; [[#Chakravorty--2017|Chakravorty et al. 2017]] ), with possible knock-on effects related to civil unrest ( [[#Abbott--2017|Abbott et al. 2017]] ; [[#D’Odorico--2018|D’Odorico et al. 2018]] ).

Developing new bio-based solutions while mitigating overall biomass demand growth

Many existing bio-based products have significant mitigation potential. Increased use of wood in buildings can reduce GHG emissions from cement and steel production while providing carbon storage ( [[#Churkina--2020|Churkina et al. 2020]] ). Substitution of fossil fuels with biomass in manufacture of cement and steel can reduce GHG emissions where these materials are difficult to replace. Dispatchable power based on biomass can provide power stability and quality as the contribution from solar and wind power increases (AR6 WGIII Chapter 6), and biofuels can contribute to reducing fossil fuel emissions in the transport and industry sectors (AR6 WGIII Chapters 10 and 11). The use of bio-based plastics, chemicals and packaging could be increased, and biorefineries can achieve high resource-use efficiency in converting biomass into food, feed, fuels and other bio-based products ( [[#Aristizábal‐Marulanda--2019|Aristizábal‐Marulanda and Cardona Alzate 2019]] ; [[#Schmidt--2019|Schmidt et al. 2019]] ). There is also scope for substituting existing bio-based products with more benign products. For example, cellulose-based textiles can replace cotton, which requires large amounts of water, chemical fertilisers and pesticides to ensure high yields.

While increasing and diversified use of biomass can reduce the need for fossil fuels and other GHG-intensive products, unfavourable GHG balances may limit the mitigation value. Growth in biomass use may in the longer term also be constrained by the need to protect biodiversity and ecosystems’ capacity to support essential ecosystem services. Biomass use may also be constrained by water scarcity and other resource scarcities, and/or challenges related to public perception and acceptance due to impacts caused by biomass production and use. Energy conservation and efficiency measures and deployment of technologies and systems that do not rely on carbon, such as carbon-free electricity supporting, ''inter alia'' , electrification of transport as well as industry processes and residential heating ( [[#IPCC--2018|IPCC 2018]] ; [[#UNEP--2019|UNEP 2019]] ), can constrain the growth in biomass demand when countries seek to phase out fossil fuels and other GHG-intensive products while providing an acceptable standard of living. Nevertheless, demand for bio-based products may become high where full decoupling from carbon is difficult to achieve (e.g., aviation, bio-based plastics and chemicals) or where carbon storage is an associated benefit (e.g., wood buildings, BECCS, biochar for soil amendments), leading to challenging trade-offs (e.g., food security, biodiversity) that need to be managed in environmentally sustainable and socially just ways.

Changes on the demand side as well as improvements in resource-use efficiencies within the global food and other bio-based systems can also reduce pressures on the remaining land resources. For example, dietary changes toward more plant-based food (where appropriate) and reduced food waste can provide climate change mitigation along with health benefits ( [[#Willett--2019|Willett et al. 2019]] ) (AR6 WGIII Sections 7.4 and 12.4) and other co-benefits with regard to food security, adaptation and land use ( [[#Mbow--2019|Mbow et al. 2019]] ; [[#Smith--2019a|Smith et al. 2019a]] ) (AR6 WGII Chapter 5). Advancements in the provision of novel food and feed sources (e.g., cultured meat, insects, grass-based protein feed and cellular agriculture) can also limit the pressures on finite natural resources ( [[#Parodi--2018|Parodi et al. 2018]] ; [[#Zabaniotou--2018|Zabaniotou 2018]] ) (AR6 WGIII [[#12.4|Section 12.4]] ).

Cross-Working Group Box 3

Circular bioeconomy

Circular economy approaches (AR6 WGIII [[#12.6|Section 12.6]] ) are commonly depicted by two cycles, where the biological cycle focuses on regeneration in the biosphere and the technical cycle focuses on reuse, refurbishment and recycling to maintain value and maximise material recovery ( [[#Mayer--2019a|Mayer et al. 2019a]] ). Biogenic carbon flows and resources are part of the biological carbon cycle, but carbon-based products can be included in, and affect, both the biological and the technical carbon cycles ( [[#Kirchherr--2017|Kirchherr et al. 2017]] ; [[#Winans--2017|Winans et al. 2017]] ; [[#Velenturf--2019|Velenturf et al. 2019]] ). The integration of circular economy and bioeconomy principles has been discussed in relation to organic waste management ( [[#Teigiserova--2020|Teigiserova et al. 2020]] ), societal transition and policy development ( [[#European%20Commission--2018|European Commission 2018]] ; [[#Bugge--2019|Bugge et al. 2019]] ) as well as COVID-19 recovery strategies ( [[#Palahí--2020|Palahí et al. 2020]] ). To maintain the natural resource base, circular bioeconomy emphasises sustainable land use and the return of biomass and nutrients to the biosphere when it leaves the technical cycle.

Scarcity is an argument for adopting circular economy principles for the management of biomass, as for non-renewable resources. Waste avoidance, product reuse and material recycling keep down resource use while maintaining product and material value. However, reuse and recycling are not always feasible, for example when biofuels are used for transport and bio-based biodegradable chemicals are used to reduce ecological impacts, where losses to the environment are unavoidable. A balanced approach to management of biomass resources could start from the perspective of value preservation within the carbon cycle, with possible routes for biomass use based on the carbon budget defined by the Paris Agreement, principles for sustainable land use and natural ecosystem protection.

Land-use opportunities and challenges in the bioeconomy

Analyses of synergies and trade-offs between adaptation and mitigation in the agriculture and forestry sectors show that outcomes depend on context, design and implementation, so actions have to be tailored to the specific conditions to minimise adverse effects ( [[#Kongsager--2018|Kongsager 2018]] ). This is supported in literature analysing the nexus between land, water, energy and food in the context of climate change, which consistently concludes that addressing these different domains together rather than in isolation would enhance synergies and reduce trade-offs ( [[#Obersteiner--2016|Obersteiner et al. 2016]] ; [[#D’Odorico--2018|D’Odorico et al. 2018]] ; [[#Soto%20Golcher--2018|Soto Golcher and Visseren-Hamakers 2018]] ; [[#Froese--2019|Froese et al. 2019]] ; [[#Momblanch--2019|Momblanch et al. 2019]] ).

Nature-based solutions addressing climate change can provide opportunities for sustainable livelihoods as well as multiple ecosystem services, such as flood risk management through floodplain restoration, saltmarshes, mangroves or peat renaturation ( [[#UNEP--2021|UNEP 2021]] ; AR6 WGII Cross-Chapter Box NATURAL). Climate-smart agriculture can increase productivity while enhancing resilience and reducing GHG emissions inherent to production ( [[#Lipper--2014|Lipper et al. 2014]] ; [[#Bell--2018|Bell et al. 2018]] ; [[#FAO--2019b|]] [[#FAO--2019|FAO 2019]] b ; [[#Singh--2021|Singh and Chudasama 2021]] ). Similarly, climate-smart forestry considers the whole value chain and integrates climate objectives into forest sector management through multiple measures (from strict reserves to more intensively managed forests) providing mitigation and adaptation benefits ( [[#Nabuurs--2018|Nabuurs et al. 2018]] ; [[#Verkerk--2020|Verkerk et al. 2020]] ) (AR6 WGIII [[IPCC:Wg3:Chapter:Chapter-7#7.3|Section 7.3]] ).

Cross-Working Group Box 3

Agroecological approaches can be integrated into a wide range of land management practices to support a sustainable bioeconomy and address equity considerations ( [[#HLPE--2019|HLPE 2019]] ). Relevant land-use practices, such as agroforestry, intercropping, organic amendments, cover crops and rotational grazing, can provide mitigation and support adaption to climate change via food security, livelihoods, biodiversity and health co-benefits ( [[#Ponisio--2015|Ponisio et al. 2015]] ; [[#Garibaldi--2016|Garibaldi et al. 2016]] ; [[#D’Annolfo--2017|D’Annolfo et al. 2017]] ; [[#Bezner%20Kerr--2019|Bezner Kerr et al. 2019]] ; [[#Clark--2019|Clark et al. 2019]] b; [[#Córdova--2019|Córdova et al. 2019]] ; [[#HLPE--2019|HLPE 2019]] ; [[#Mbow--2019|Mbow et al. 2019]] ; [[#Renard--2019|Renard and Tilman 2019]] ; [[#Sinclair--2019|Sinclair et al. 2019]] ; [[#Bharucha--2020|Bharucha et al. 2020]] ; [[#Bezner%20Kerr--2021|Bezner Kerr et al. 2021]] ) (AR6 WGII Cross-Chapter Box NATURAL). Strategic integration of appropriate biomass production systems into agricultural landscapes can provide biomass for bioenergy and other bio-based products while providing co-benefits such as enhanced landscape diversity, habitat quality, retention of nutrients and sediment, erosion control, climate regulation, flood regulation, pollination and biological pest and disease control ( [[#Christen--2013|Christen and Dalgaard 2013]] ; [[#Asbjornsen--2014|Asbjornsen et al. 2014]] ; [[#Holland--2015|Holland et al. 2015]] ; [[#Ssegane--2015|Ssegane et al. 2015]] ; [[#Dauber--2016|Dauber and Miyake 2016]] ; [[#Milner--2016|Milner et al. 2016]] ; [[#Ssegane--2016|Ssegane and Negri 2016]] ; [[#Styles--2016|Styles et al. 2016]] ; [[#Zumpf--2017|Zumpf et al. 2017]] ; [[#Cacho--2018|Cacho et al. 2018]] ; [[#Alam--2019|Alam and Dwivedi 2019]] ; [[#Cubins--2019|Cubins et al. 2019]] ; [[#HLPE--2019|HLPE 2019]] ; [[#Olsson--2019|Olsson et al. 2019]] ; [[#Zalesny--2019|Zalesny et al. 2019]] ; Englund et al. 2020) (AR6 WGIII Box 12.3). Such approaches can help limit environmental impacts from intensive agriculture while maintaining or increasing land productivity and biomass output.

Transitions from conventional to new biomass production and conversion systems include challenges related to cross-sector integration and limited experience with new crops and land use practices, including needs for specialised equipment ( [[#Thornton--2015|Thornton and Herrero 2015]] ; [[#HLPE--2019|HLPE 2019]] ) (AR6 WGII [[IPCC:Wg3:Chapter:Chapter-5#5.1|Section 5.1]] 0). Introduction of agroecological approaches and integrated biomass/food crop production can result in lower food crop yields per hectare, particularly during transition phases, potentially causing indirect landuse change, but can also support higher and more stable yields, reduce costs, and increase profitability under climate change ( [[#Muller--2017|Muller et al. 2017]] ; [[#Seufert--2017|Seufert and Ramakutty 2017]] ; [[#Barbieri--2019|Barbieri et al. 2019]] ; [[#HLPE--2019|HLPE 2019]] ; [[#Sinclair--2019|Sinclair et al. 2019]] ; [[#Smith--2019a|Smith et al. 2019a]] ; [[#Smith--2020|Smith et al. 2020]] ). Crop diversification, organic amendments, and biological pest control ( [[#HLPE--2019|HLPE 2019]] ) can reduce input costs and risks of occupational pesticide exposure and food and water contamination ( [[#González-Alzaga--2014|González-Alzaga et al. 2014]] ; [[#EFSA--2017|EFSA 2017]] ; [[#Mie--2017|Mie et al. 2017]] ), reduce farmers’ vulnerability to climate change (e.g., droughts and spread of pests and diseases affecting plant and animal health) ( [[#Delcour--2015|Delcour et al. 2015]] ; [[#FAO--2020|FAO 2020]] ) and enhance provisioning and sustaining ecosystem services, such as pollination ( [[#D’Annolfo--2017|D’Annolfo et al. 2017]] ; [[#Sinclair--2019|Sinclair et al. 2019]] ).

Barriers toward wider implementation include absence of policies that compensate land owners for providing enhanced ecosystem services and other environmental benefits, which can help overcome short-term losses during the transition from conventional practices before longer-term benefits can accrue. Other barriers include limited access to markets, knowledge gaps, financial, technological or labour constraints, lack of extension support and insecure land tenure ( [[#Jacobi--2017|Jacobi et al. 2017]] ; [[#Kongsager--2017|Kongsager 2017]] ; [[#Hernández-Morcillo--2018|Hernández-Morcillo et al. 2018]] ; [[#Iiyama--2018|Iiyama et al. 2018]] ; [[#HLPE--2019|HLPE 2019]] ). Regional-level agroecology transitions may be facilitated by co-learning platforms, farmer networks, private sector, civil society groups, regional and local administration and other incentive structures (e.g., price premiums, access to credit, regulation) ( [[#Coe--2014|Coe et al. 2014]] ; [[#Pérez-Marin--2017|Pérez-Marin et al. 2017]] ; Mier y Terán Giménez [[#Cacho--2018|Cacho et al. 2018]] ; [[#HLPE--2019|HLPE 2019]] ; [[#Valencia--2019|Valencia et al. 2019]] ; SAEPEA 2020). With the right incentives, improvements can be made with regard to profitability, making alternatives more attractive to land owners.

Governing the solution space

Literature analysing the synergies and trade-offs between competing demands for land suggest that solutions are highly contextualised in terms of their environmental, socio-economic and governance-related characteristics, making it difficult to devise generic solutions ( [[#Haasnoot--2020|Haasnoot et al. 2020]] ). Aspects of spatial and temporal scale can further enhance the complexity, for instance where transboundary effects across jurisdictions or upstream-downstream characteristics need to be considered, or where climate change trajectories might alter relevant biogeophysical dynamics ( [[#Postigo--2021|Postigo and Young 2021]] ). Nonetheless, there is broad agreement that taking the needs and perspectives of multiple stakeholders into account in a transparent process during negotiations improves the chances of achieving outcomes that maximise synergies while limiting trade-offs ( [[#Ariti--2018|Ariti et al. 2018]] ; [[#Metternicht--2018|Metternicht 2018]] ; [[#Favretto--2020|Favretto et al. 2020]] ; [[#Kopáček--2021|Kopáček 2021]] ; [[#Muscat--2021|Muscat et al. 2021]] ). Yet differences in agency and power between stakeholders or anticipated changes in access to or control of resources can undermine negotiation results even if there is a common understanding of the overarching benefits of more integrated environmental agreements and the need for greater coordination and cooperation to avoid longer-term losses to all ( [[#Aarts--2010|Aarts and Leeuwis 2010]] ; [[#Weitz--2017|Weitz et al. 2017]] ). There is also the risk that strong local participatory processes can become disconnected from broader national plans, and thus fail to support the achievement of national targets. Thus, connection between levels is needed to ensure that ambition for transformative change is not derailed at local level ( [[#Aarts--2010|Aarts and Leeuwis 2010]] ; [[#Postigo--2021|Postigo and Young 2021]] ).

Decisions on land uses between biomass production for food, feed, fibre or fuel, as well as nature conservation or restoration and other uses (e.g., mining, urban infrastructure), depend on differences in perspectives and values. Because the availability of land for diverse biomass uses is invariably limited, setting priorities for land-use allocations therefore first depends on making the perspectives underlying what is considered as ‘high-value’ explicit ( [[#Fischer--2007|Fischer et al. 2007]] ; [[#Garnett--2015|Garnett et al. 2015]] ; [[#De%20Boer--2018|De Boer and Van Ittersum 2018]] ;

Cross-Working Group Box 3

[[#Muscat--2020|Muscat et al. 2020]] ). Decisions can then be made transparently based on societal norms, needs and the available resource base. Prioritisation of land use for the common good therefore requires societal consensus building embedded in the socio-economic and cultural fabric of regions, societies and communities. Integration of local decision-making with national planning ensures local actions complement national development objectives.

International trade in the global economy today provides important opportunities to connect producers and consumers, effectively buffering price volatilities and potentially offering producer countries access to global markets, which can be seen as an effective adaptation measure ( [[#Baldos--2015|Baldos and Hertel 2015]] ; [[#Costinot--2016|Costinot et al. 2016]] ; [[#Hertel--2016|Hertel and Baldos 2016]] ; [[#Gouel--2021|Gouel and Laborde 2021]] ) (AR6 WGII [[IPCC:Wg3:Chapter:Chapter-5#5.1|Section 5.1]] 1). But there is also clear evidence that international trade and the global economy can enhance price volatility, lead to food price spikes and affect food security due to climate and other shocks, as seen recently due to the COVID-19 pandemic ( [[#Cottrell--2019|Cottrell et al. 2019]] ; [[#WFP-FSIN--2020|WFP-FSIN 2020]] ; [[#Verschuur--2021|Verschuur et al. 2021]] ) (AR6 WGII [[IPCC:Wg3:Chapter:Chapter-5#5.1|Section 5.1]] 2). The continued strong demand for food and other bio-based products, mainly from high- and middle-income countries, therefore requires better cooperation between nations and global governance of trade to more accurately reflect and disincentivise their environmental and social externalities. Trade in agricultural and extractive products driving land-use change in tropical forest and savanna biomes is of major concern because of the biodiversity impacts and GHG emissions incurred in their provision ( [[#Hosonuma--2012|Hosonuma et al. 2012]] ; [[#Forest%20Trends--2014|Forest Trends 2014]] ; [[#Smith--2014|Smith et al. 2014]] ; [[#Henders--2015|Henders et al. 2015]] ; [[#Curtis--2018|Curtis et al. 2018]] ; [[#Pendrill--2019|Pendrill et al. 2019]] ; [[#Seymour--2019|Seymour and Harris 2019]] ; [[#Kissinger--2021|Kissinger et al. 2021]] ) (AR6 WGII Tropical Forests Cross-Chapter Paper).

In summary, there is significant scope for optimising use of land resources to produce more biomass while reducing adverse effects ( ''high confidence'' ). Context-specific prioritisation, technology innovation in bio-based production, integrative policies, coordinated institutions and improved governance mechanisms to enhance synergies and minimise trade-offs can mitigate the pressure on managed as well as natural and semi-natural ecosystems ( ''medium confidence'' ). Yet, energy conservation and efficiency measures, and deployment of technologies and systems that do not rely on carbon-based energy and materials, are essential for mitigating biomass demand growth as countries pursue ambitious climate goals ( ''hi'' ''gh confidence'' ).

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