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

=== 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]] ).

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