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

=== 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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