Editing IPCC:AR6/WGII/Chapter-5 (section)

=== 5.5.3 Projected Impacts ===

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There is ''limited evidence'' on future impact of climate change on livestock production, particularly in LMICs ( [[#Rivera-Ferre--2016|Rivera-Ferre et al., 2016]] ).

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==== 5.5.3.1 Impacts on rangelands, feeds and forages ====

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Uncertainties persist regarding estimates of net primary productivity (NPP) in grazing lands ( [[#Fetzel--2017|Fetzel et al., 2017]] ; [[#Chen--2018b|Chen et al., 2018b]] ), so estimation of climate change impacts on grasslands is challenging. Mean global annual NPP is projected to decline 10 gC m −2 yr −1 in 2050 under RCP8.5, although herbaceous NPP is projected to increase slightly ( [[#Boone--2018|Boone et al., 2018]] ; see Figure 5.11). Similar estimates were made by [[#Havlik--2014|Havlik et al. (2014)]] : large increases in projected NPP in higher northern latitudes (21% increase in the USA and Canada) and large declines in western Africa (−46%) and Australia (−17%). The cumulative effects of impacts on forage productivity globally are projected to result in 7–10% declines in livestock numbers by 2050 for warming of ~2°C, representing a loss of livestock assets ranging from USD 10 to 13 billion ( [[#Boone--2018|Boone et al., 2018]] ). Changes to African grassland productivity will have substantial, negative impacts on the livelihoods of &gt;180 million people.

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[[File:bbbc672a5e564302999be245928fdce7 IPCC_AR6_WGII_Figure_5_011.png]]

'''Figure 5.11 |''' '''Regional percent changes in land cover and soil carbon from ensemble simulation results in 2050 under emissions scenario RCP8''' '''.''' '''5 compared with 1971–2000.''' Plant responses were enhanced by CO 2 fertilisation. The larger chart (lower left) shows mean changes for all rangelands, and all charts are scaled to −60% to +60% change. Shown are annual net primary productivity (ANPP), herbaceous net primary productivity (HNPP), bare ground, herbaceous (herb), shrub, and tree cover, SOC (soil carbon), above-ground live biomass and below-ground live biomass. Regions as defined by the United Nations Statistics Division. The bar for above-ground live biomass in Western Asia (*) is truncated and is 82% ( [[#Boone--2018|Boone et al., 2018]] ).

Increases in above-ground NPP, and woody cover at the expense of grassland, are projected in some of the tropical and subtropical drylands ( [[#Doherty--2010|Doherty et al., 2010]] ; [[#Ravi--2010|Ravi et al., 2010]] ; [[#Saki--2018|Saki et al., 2018]] ), in Mediterranean wood pastures ( [[#Rolo--2019|Rolo and Moreno, 2019]] ) and in the northern Great Plains of North America ( [[#Klemm--2020|Klemm et al., 2020]] ). [[#Godde--2021|Godde et al. (2021)]] projected that woody encroachment would occur on 51% of global rangeland area by 2050 under RCP8.5. The future makeup of grasslands under climate change is uncertain, given the variation in responses of the component species, though this variation may provide a climate buffer ( [[#Jones--2019|Jones, 2019]] ) ( ''low confidence'' ). C4 grass species are regarded as less responsive to elevated carbon dioxide than C3 species, though this is not always the case ( [[#Reich--2018|Reich et al., 2018]] ).

There are other interactions between climate change and grazing effects on grasslands. Li (2018a) reported strong negative responses of NPP and species richness to 4°C warming, a 50% precipitation decrease, and high grazing intensity. Changes in grassland composition will inevitably change their suitability for different grazing animal species, with switches from herbaceous grazers such as cattle to goats and camels to take advantage of increases in shrubland ( [[#Kagunyu--2014|Kagunyu and Wanjohi, 2014]] ). Rangeland feed quality may also be reduced via invasive species of lower quality than native species ( [[#Blumenthal--2016|Blumenthal et al., 2016]] ).

Warming and water deficits impair the quality and digestibility of a C4 tropical forage grass, ''Panicum maximum'' , because of increases in leaf lignin ( [[#Habermann--2019|Habermann et al., 2019]] ). A metanalysis by Dellar (2018) of climate change impacts on European pasture yield and quality found an increase in above-ground dry weight under increased CO 2 concentrations for forbs, legumes, graminoids and shrubs with reductions in N concentrations in all plant functional groups. Temperature increases will increase yields in alpine and northern areas (+82.6%) but reduce N concentrations for shrubs (−13.6%) and forbs (−18.5%).

Increased temperatures and CO 2 concentrations may increase herbaceous growth and favour legumes over grasses in mixed pastures ( [[#He--2019|He et al., 2019]] ). These effects may be modified by changes in rainfall patterns, plant competition, perennial growth habits and plant–animal interactions. The cumulative effect of these factors is uncertain. Large, persistent declines in forage quality are projected, irrespective of warming, under elevated CO 2 conditions (600 ppm and +1.5°C day/3°C night temperature increases) in North American grasslands ( [[#Augustine--2018|Augustine et al., 2018]] ). Rising CO 2 concentrations may result in losses of iron, zinc and protein in plants by up to 8% by 2050 ( [[#Smith--2018|Smith and Myers, 2018]] ). Little information is available on possible impacts on carbon-based micronutrients, such as vitamins. About 57% of grasses globally are C3 plants and thus susceptible to CO 2 effects on their nutritional quality ( [[#Osborne--2014|Osborne et al., 2014]] ). These impacts will result in greater nutritional stress in grazing animals as well as reduced meat and milk production (quality and quantity) ( ''high confidence'' , ''medium evidence'' ).

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==== 5.5.3.2 Impacts of increased temperature on livestock ====

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Recent research confirms the seriousness of the heat stress issue ( ''medium evidence'' , ''high agreement'' ). Considerable increases are projected during this century in the number of ‘extreme stress’ days per year for cattle, chicken, goat, pig and sheep populations with SSP5-8.5 but many fewer with SSP1-2.6 ( [[#Thornton--2021|Thornton et al., 2021]] : Figure 5.12; see Cross-Chapter Box MOVING PLATE in this chapter). Resulting impacts on livestock production and productivity may be large, particularly for cattle throughout the tropics and subtropics and for goats in parts of Latin America and much of Africa and Asia. Pigs are projected to be particularly affected in the mid-latitudes of Europe, East Asia and North America. [[#Lallo--2018|Lallo et al. (2018)]] estimated that global warming of 1.5°C and 2°C may exceed limits for normal thermo-regulation of livestock animals and result in persistent heat stress for animals in the Caribbean. Breed differences in heat stress resistance in dairy animals are now being quantified ( [[#Gantner--2017|Gantner et al., 2017]] ), as are effects on sow reproductive performance in temperate climates ( [[#Wegner--2016|Wegner et al., 2016]] ). Estimates of losses in milk production due to heat stress in parts of the USA, UK and West Africa to the end of the century range from 1% to 17% ( [[#Hristov--2018|Hristov et al., 2018]] ; [[#Fodor--2018|Fodor et al., 2018]] ; Wreford and Topp, 2020; [[#Rahimi--2020|Rahimi et al., 2020]] ). Much larger losses in dairy and beef production due to heat stress are projected for many parts of the tropics and subtropics: these could amount to USD 9 billion per year for dairy and USD 31 billion per for beef to end-century under SSP5-8.5, approximately 5% and 14% of the global value of production of these commodities in constant 2005 dollars.

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[[File:3750c6aa5275494e5a09d0fbf3baa129 IPCC_AR6_WGII_Figure_5_012.png]]

'''Figure 5.12 |''' '''Change in the number of days per year above ‘extreme stress’ values from the early 21st century (1991–2010) to end of century (2081–2100), estimated under SSP1-2''' '''.''' '''6 and SSP5-8.5 using the Temperature Humidity Index (THI).''' Mapped for species current global distribution ( [[#Gilbert--2018|Gilbert et al., 2018]] ) (grey areas, no change). ( [[#Thornton--2021|Thornton et al., 2021]] ), Also see Annex I: Global to Regional Atlas.

In many LMICs, poultry contribute significantly to rural livelihoods, including via modest improvements in nutritional outcomes of household children ( [[#de%20Bruyn--2018|de Bruyn et al., 2018]] ). Rural poultry are generally assumed to be hardy and well adapted to stressful environments, but little information exists regarding their performance under warmer climates or interactions with other production challenges ( [[#Nyoni--2019|Nyoni et al., 2019]] ).

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==== 5.5.3.3 Impacts on livestock diseases ====

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The impacts of climate change on livestock diseases remain highly uncertain ( ''medium evidence'' , ''high agreement'' ). [[#Bett--2017|Bett et al. (2017)]] showed positive associations between rising temperature and expansion of the geographical ranges of arthropod vectors such as ''Culicoides imicola'' , which transmits the bluetongue virus. A 1-in-20-year bluetongue outbreak at present-day temperatures is projected to increase in frequency to 1-in-5 to 1-in-7 years by the 2050s, under RCP4.5 and RCP8.5, although animal movement restrictions can prevent devastating outbreaks ( [[#Jones--2019|Jones et al., 2019]] ).

The prevalence and occurrence of some livestock diseases are positively associated with extreme weather events ( ''high confidence'' ). There are high risks of future Rift Valley fever (RVF) outbreaks under both RCP4.5 and RCP8.5 this century in East Africa and beyond ( [[#Taylor--2016|Taylor et al., 2016]] ; [[#Mweya--2017|Mweya et al., 2017]] ).

Few studies explicitly consider the biotic and abiotic factors that interact additively, multiplicatively or antagonistically to influence host–pathogen dynamics ( [[#Cable--2017|Cable et al., 2017]] ). Integrative concepts that aim to improve the health of people, animals and the environment such as One Health may offer a framework for enhancing understanding of these complex interactions ( [[#Zinsstag--2018|Zinsstag et al., 2018]] ). Much remains unknown concerning disease transmission dynamics under a warming climate ( [[#Heffernan--2018|Heffernan, 2018]] ), highlighting the need for effective monitoring of livestock disease ( [[#Brito--2017|Brito et al., 2017]] ; [[#Hristov--2018|Hristov et al., 2018]] ).

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==== 5.5.3.4 Impacts on livestock and water resources ====

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Water resources for livestock may decrease in places because of increased runoff and reduced groundwater resources, as well as decreased groundwater availability in some environments (AR5). Increased temperatures will cause changes in river flow and the amount of water stored in basins, potentially leading to increased water stress in dry areas such as parts of the Volta River Basin ( [[#Mul--2015|Mul et al., 2015]] ). Toure (2017) estimated decreases in groundwater recharge rates of 49% and of stored groundwater by 24% to the 2030s in the Klela Basin in Mali under both RCP4.5 and RCP8.5, with potentially serious consequences for water availability for livestock and irrigation.

Water intake by livestock is related to species, breed, animal size, age, diet, animal activity, temperature and physiological status of animals ( [[#Henry--2018|Henry et al., 2018]] ). Direct water use by cattle may increase by 13% for a temperature increase of 2.7°C in a subtropical region ( [[#Harle--2007|Harle et al., 2007]] ). Changes in water availability may arise because of decreased supply or increased competition from other sectors. Availability changes may be accompanied by shifts in water quality, such as increased levels of microorganisms and algae, that can negatively affect livestock health ( [[#Naqvi--2015|Naqvi et al., 2015]] ). In arid lands, projected decreases in water availability will severely compromise reproductive performance and productivity in sheep ( [[#Naqvi--2017|Naqvi et al., 2017]] ). In higher-input livestock systems, water costs may increase substantially owing to increased competition for water ( [[#Rivera-Ferre--2016|Rivera-Ferre et al., 2016]] ).

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==== 5.5.3.5 Livestock and climate variability ====

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Information on future climate variability changes on livestock system productivity does not exist yet. Increases in climate variability may increase food insecurity in the future, mediated through increased crop and livestock production variability ( [[#Thornton--2014|Thornton and Herrero, 2014]] ) in LMICs. Rainfall variability increases in pastoral lands have been linked to declining cattle numbers ( [[#Megersa--2014|Megersa et al., 2014]] ). Changes in future climate variability may have large negative impacts on livestock system outcomes ( [[#Sloat--2018|Sloat et al., 2018]] ; [[#Stanimirova--2019|Stanimirova et al., 2019]] ); these effects can be larger than those associated with gradual climate change ( ''limited evidence'' , ''medium agreement'' ) ( [[#Godde--2019|Godde et al., 2019]] ). In grasslands, [[#Chang--2017|Chang et al. (2017)]] (Europe) and [[#Godde--2020|Godde et al. (2020)]] (globally) projected increases in biomass inter-annual variability, the worst effects occurring in rangeland communities that are already vulnerable. Ways in which climate variability impacts have been addressed in the past, such as via herd mobility, may become increasingly unviable in the future ( [[#Hobbs--2008|Hobbs et al., 2008]] ).

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==== 5.5.3.6 Societal impacts within the production system ====

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Livestock play important social ( [[#Kitalyi--2005|Kitalyi et al., 2005]] ) and cultural ( [[#Gandini--2003|Gandini and Villa, 2003]] ) roles in many societies. Climate change will negatively affect the provisioning of social benefits in many of the world’s grasslands ( ''medium confidence'' ). Examples include moving to semi-private land ownership models, driven in part by climate change, that are changing social networks and limiting socio-ecological resilience in pastoral systems in East Africa ( [[#Kibet--2016|Kibet et al., 2016]] ; [[#Bruyere--2018|Bruyere et al., 2018]] ) and Asia ( [[#Cao--2018a|Cao et al., 2018a]] ); altering traditional food, resource and medicine sharing mechanisms in West Africa ( [[#Boafo--2016|Boafo et al., 2016]] ); and the limited ability of current livestock systems to satisfy societies’ demand for CES in Northwest Europe ( [[#Bengtsson--2019|Bengtsson et al., 2019]] ). The societal impacts of climate change on livestock systems may interact with drivers of change and increase herders’ vulnerability via processes of sedentarisation and land fragmentation, both of which may result in decreased animal access to rangelands ( [[#Adhikari--2015|Adhikari et al., 2015]] ; Cross-Chapter Box MOVING PLATE this chapter). Stronger linkages are needed between ecosystem service and food security research and policy to address these challenges ( [[#Gentle--2016|Gentle and Thwaites, 2016]] ; [[#Bengtsson--2019|Bengtsson et al., 2019]] ).

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