Editing IPCC:AR6/WGII/Chapter-9 (section)

=== 9.6.1 Observed Impacts of Climate Change on African Biodiversity and Ecosystem Services ===

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==== 9.6.1.1 Terrestrial Ecosystems ====

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The overall continental trend is woody plant expansion, particularly in grasslands and savannas, with woody plant cover increasing at a rate of 2.4% per decade (see Figure 9.17; [[#Stevens--2017|Stevens et al., 2017]] ; [[#Axelsson--2018|Axelsson and Hanan, 2018]] ). There is also increased grass cover in arid regions in southwestern Africa ( [[#Masubelele--2014|Masubelele et al., 2014]] ). There is ''high agreement'' that this is attributable to increased CO 2 , warmer and wetter climates, declines in burned area and release from herbivore browsing pressure, but the relative importance of these interacting drivers remains uncertain ( [[#O’Connor--2014|O’Connor et al., 2014]] ; [[#Stevens--2016|Stevens et al., 2016]] ; [[#García%20Criado--2020|García Criado et al., 2020]] ). Woody encroachment is the dominant trend in the western and central Sahel, occurring over 24% of the region, driven primarily by shifts in rainfall timing and recovery from drought ( [[#Anchang--2019|Anchang et al., 2019]] ; [[#Brandt--2019|Brandt et al., 2019]] ). Remote sensing studies demonstrate greening in southern Africa and forest expansion into water-limited savannas in central and west Africa ( [[#Baccini--2017|Baccini et al., 2017]] ; [[#Aleman--2018|Aleman et al., 2018]] ; [[#Piao--2020|Piao et al., 2020]] ), with increases in precipitation and atmospheric CO 2 the probable determinants of change ( [[#Venter--2018|Venter et al., 2018]] ; [[#Brandt--2019|Brandt et al., 2019]] ; [[#Zhang--2019|Zhang et al., 2019]] ). These trends of greening and woody plant expansion stand in contrast to the desertification and contraction of vegetated areas highlighted in AR5 ( [[#Niang--2014|Niang et al., 2014]] ), but are based on multiple studies and longer time series of observations. Reported cases of desertification and vegetation loss, for example, in the Sahel, appear transitory and localised rather than widespread and permanent ( [[#Dardel--2014|Dardel et al., 2014]] ; [[#Pandit--2018|Pandit et al., 2018]] ; [[#Sterk--2020|Sterk and Stoorvogel, 2020]] ).

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[[File:29c1d31d22d4753decc5ef662d422044 IPCC_AR6_WGII_Figure_9_017.png]]

'''Figure 9.17 |''' '''Widespread changes to African vegetation have been reported, especially increasing woody plant cover in many savannas and grasslands, with 37% of these changes proposed to be driven by human-caused climate change and increased CO''' '''2''' '''(a)'''. The warming of lakes and rivers has been detected across Africa and is attributed to climate change. Data on vegetation change was gathered from 156 studies published between 1989 and 2021 '''(b)''' . Climatic changes, mostly associated with changes in rainfall, are enhancing grass production in arid grasslands and savannas, and causing grass expansion into semi-desert regions with notable increases in the Sahel and southern Africa. Tropical forest expansion into mesic savannas is occurring on the fringes of the central African tropical forest. Interactions between land use, climate change and increasing atmospheric CO 2 concentrations are causing a widespread increase in woody plant cover encroachment in tropical savannas and grasslands. Some tree death and woody cover decline associated with climate and land use change have also been recorded across biomes. Of the reported changes to terrestrial vegetation, 24% were explicitly linked to climate change and a further 13% were proposed to be driven by climate change. In 48% of studies, no climate driver was mentioned and in 15% climate change was ruled out as the driver of change. Annual surface water temperatures in African lakes have warmed at a rate of 0.05°C–0.76°C per decade. Both satellite-based measures spanning 1985–2011 and ''in situ'' measurements spanning 1927–2014 agree on this warming trend. Other surface waters across Africa warmed from 1979–2018 at a rate of between 0.05°C and 0.5°C per decade ( [[#Woolway--2020|Woolway and Maberly, 2020]] ). Vegetation change data were taken from a larger, global literature survey of existing databases supplemented with newer studies documenting changes in tree, shrub and grass cover linked to climate and land use change in natural and semi-natural areas (for further details see [[IPCC:Wg2:Chapter:Chapter-2#2.4.3.5|Section 2.4.3.5]] ; Table SM2.1; Table SM9.2 for Africa vegetation change data and Table SM9.3 for studies reporting lake warming data).

Shifts in demography, geographic ranges, and abundance of plants and animals consistent with expected impacts of climate change are evident across Africa. These include uphill contractions of elevational range limits of birds ( [[#Neate-Clegg--2021|Neate-Clegg et al., 2021]] ), changes in species distributions previously reported in AR5 ( [[#Niang--2014|Niang et al., 2014]] ) and the death of many of the oldest and largest African baobabs ( [[#Patrut--2018|Patrut et al., 2018]] ). An increase in frequency and intensity of hot, dry weather after wildfires has led to a long-term decline in plant biodiversity in Fynbos since the 1960s ( [[#Slingsby--2017|Slingsby et al., 2017]] ). Increasing temperatures may have contributed to the declining abundance and range size of South African birds ( [[#Milne--2015|Milne et al., 2015]] ), including Cape Rockjumper ( ''Chaetops frenatus'' ) and protea canary ( ''Serinus leucopterus'' ), from increased risk of reproductive failure ( [[#Lee--2016|Lee and Barnard, 2016]] ; [[#Oswald--2020|Oswald et al., 2020]] ). For hot and dry regions (e.g., Kalahari), there is strong evidence that increased temperatures are having chronic sublethal impacts, including reduced foraging efficiency and loss of body mass ( [[#du%20Plessis--2012|du Plessis et al., 2012]] ; [[#Conradie--2019|Conradie et al., 2019]] ), and are approaching species physiological limits, with heat extremes driving mass mortality events in birds and bats ( [[#McKechnie--2021|McKechnie et al., 2021]] ). Vegetation change linked to climate change and increasing atmospheric CO 2 has had an indirect impact on animals. Increased woody cover has decreased the occurrence of bird, reptile and mammal species that require grassy habitats ( [[#Péron--2015|Péron and Altwegg, 2015]] ; [[#McCleery--2018|McCleery et al., 2018]] ). Decreased fruit production linked to rising temperatures has decreased the body condition of fruit-dependent forest elephants by 11% from 2008–2018 ( [[#Bush--2020|Bush et al., 2020]] ).

There is ''high agreement'' that land use activities counteract or exacerbate climate-driven vegetation change ( [[#Aleman--2017|Aleman et al., 2017]] ; [[#Timm%20Hoffman--2019|Timm Hoffman et al., 2019]] ). Decreased woody plant biomass in 11% of sub-Saharan Africa was attributed to land clearing for agriculture ( [[#Brandt--2017|Brandt et al., 2017]] ; [[#Ordway--2017|Ordway et al., 2017]] ). Localised loss of tree cover in Miombo woodlands and 16.6±0.5 Mha of forest loss in the Congo Basin between 2000–2014 was driven largely by forest clearing and drought mortality ( [[#McNicol--2018|McNicol et al., 2018]] ; [[#Tyukavina--2018|Tyukavina et al., 2018]] ).

Vegetation changes interacting with climate and land use change have impacted fire regimes across Africa. The frequency of weather conducive for fire has increased in southern and west Africa and is expected to continue increasing in the 21st century under both RCP2.6 and RCP8.5 ( [[#Betts--2015|Betts et al., 2015]] ; [[#Abatzoglou--2019|Abatzoglou et al., 2019]] ). Increased grass cover in arid regions introduced fire into regions where fuel was previously insufficient to allow fire spread, such as the arid Karoo in South Africa ( [[#du%20Toit--2015|du Toit et al., 2015]] ; [[#Strydom--2016|Strydom and Savage, 2016]] ). In contrast, shrub encroachment, increased precipitation ( [[#Zubkova--2019|Zubkova et al., 2019]] ), vegetation fragmentation and cropland expansion have reduced fire activity in many African grasslands and savannas ( [[#Andela--2014|Andela and van der Werf, 2014]] ; [[#Probert--2019|Probert et al., 2019]] ). These drivers are expected to negate the effect of increasing fire weather and ultimately lead to a reduction in the total burned area under RCP4.5 and RCP8.5 ( [[#Knorr--2016|Knorr et al., 2016]] ; [[#Moncrieff--2016|Moncrieff et al., 2016]] ; [[#Wu--2016|Wu et al., 2016]] ).

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==== 9.6.1.2 Vegetation Resilience ====

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African ecosystems have a long evolutionary association with fire, large mammal herbivory and drought ( [[#Maurin--2014|Maurin et al., 2014]] ; [[#Charles-Dominique--2016|Charles-Dominique et al., 2016]] ). The maintenance of biodiversity depends on natural disturbance regimes. Natural regrowth of savanna plant biomass in southern Africa compensated for biomass removal through human activities ( [[#McNicol--2018|McNicol et al., 2018]] ), and rapid recovery occurred after the 2014–2016 extreme drought ( [[#Abbas--2019|Abbas et al., 2019]] ). During the same drought event, browsing and mixed feeder herbivores were resilient, but grazers declined by approximately 60% and were highly dependent on drought refugia ( [[#Abraham--2019|Abraham et al., 2019]] ). African tropical forests remained a carbon sink through the record drought and temperature experienced in the 2015–2016 El Niño, indicating resilience in the face of extreme environmental conditions ( [[#Bennett--2021|Bennett et al., 2021]] ). This is likely due to the presence of drought-tolerant species and floristic and functional shifts in tree species assemblages ( [[#Fauset--2012|Fauset et al., 2012]] ; [[#Aguirre-Gutiérrez--2019|Aguirre-Gutiérrez et al., 2019]] ). This resilience indicates that there is the capacity to recover from disturbances and short-term change. However, resilience has limits and beyond certain points, change can lead to irreversible shifts to different states (Figure 9.18).

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[[File:2231fbaa13ecb25d4097f6b0d5a9d818 IPCC_AR6_WGII_Figure_9_018.png]]

'''Figure 9.18 |''' '''Increases in atmospheric CO''' '''2''' '''and changes in aridity are projected to shift the geographic distribution of major biomes across Africa (''' '''high confidence''' ''').''' Arrows in the diagram indicate possible pathways of biome change from current conditions resulting from changes in CO 2 and aridity. Changes need not be gradual or linear and may occur rapidly if tipping points are crossed. Currently, widespread greening observed in Africa has been at least partially attributed to increasing atmospheric CO 2 concentrations. Future projected increases in aridity are expected to cause desertification in many regions, but it is highly uncertain how this will interact with the greening effect of CO 2 . Inset maps show the projected geographical extent of changes in CO 2 concentrations and aridity. CO 2 is projected to increase globally under all future emission scenarios. Aridity index maps show projected change in aridity (calculated as annual precipitation/annual potential evapotranspiration) at around 4°C global warming relative to 1850–1900 (RCP8.5 in 2070–2099) from 34 CMIP5 models ( [[#Scheff--2017|Scheff et al., 2017]] ). Shaded areas indicate regions where &gt;75% of models agree on the direction of change.

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==== 9.6.1.3 Freshwater Ecosystems ====

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Small climatic variations have large impacts on ecosystem function in Africa’s freshwaters ( [[#Ndebele-Murisa--2014|Ndebele-Murisa, 2014]] ; [[#Ogutu-Ohwayo--2016|Ogutu-Ohwayo et al., 2016]] ). Warming of water temperatures from 0.2°C to 3.2°C occurred in several lakes over 1927–2014 and has been attributed to human-caused climate change (Figure 9.17; [[#Ogutu-Ohwayo--2016|Ogutu-Ohwayo et al., 2016]] ). Increased temperature, changes in rainfall and reduced wind speed altered the physical and chemical properties of inland water bodies, affecting water quality and productivity of algae, invertebrates and fish ( ''high confidence'' ). In deeper lakes, warmer surface waters and decreasing wind speeds reduced shallow waters mixing with nutrient-rich deeper waters, reducing biological productivity in the upper sunlit zone ( [[#Ndebele-Murisa--2014|Ndebele-Murisa, 2014]] ; [[#Saulnier-Talbot--2014|Saulnier-Talbot et al., 2014]] ). In several lakes, climate change was identified as causing changes in insect emergence time ( [[#Dallas--2014|Dallas and Rivers-Moore, 2014]] ) and in loss of fish habitats ( [[#Natugonza--2015|Natugonza et al., 2015]] ; [[#Gownaris--2016|Gownaris et al., 2016]] ). This set of changes can harm human livelihoods, for example, from reduced fisheries productivity (see [[#9.8.5|Section 9.8.5]] ; [[#Ndebele-Murisa--2014|Ndebele-Murisa, 2014]] ; [[#Ogutu-Ohwayo--2016|Ogutu-Ohwayo et al., 2016]] ) and reduced water supply and quality ( [[#9.7.1|Section 9.7.1]] ).

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==== 9.6.1.4 Marine Ecosystems ====

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Anthropogenic climate change is already negatively impacting Africa’s marine biodiversity, ecosystem functioning and services by changing physical and chemical properties of seawater (increased temperature, salinity and acidification, and changes in oxygen concentration, ocean currents and vertical stratification) ( ''high confidence'' ) ( [[#Hoegh-Guldberg--2014|Hoegh-Guldberg et al., 2014]] ; 2018). Coastal ecosystems in west Africa are among the most vulnerable because of extensive low-lying deltas exposed to sea level rise, erosion, saltwater intrusion and flooding ( [[#Belhabib--2016|Belhabib et al., 2016]] ; [[#UNEP--2016b|UNEP, 2016b]] ; [[#Kifani--2018|Kifani et al., 2018]] ). In southern Africa, shifting distributions of anchovy, sardine, hake, rock lobster and seabirds have been partly attributed to climate change ( [[#Crawford--2015|Crawford et al., 2015]] ; [[#van%20der%20Lingen--2018|van der Lingen and Hampton, 2018]] ; [[#Vizy--2018|Vizy et al., 2018]] ), including southern shifts of 30 estuarine and marine fish species attributed to increased temperature and changes in water circulation from decreased river inflow ( [[#Augustyn--2018|Augustyn et al., 2018]] ). Warming sea surface temperatures inhibiting nutrient mixing have reduced phytoplankton biomass in the western Indian Ocean by 20% since the 1960s, potentially reducing tuna catches ( [[#Roxy--2016|Roxy et al., 2016]] ).

Mangroves, seagrasses and coral reefs support nursery habitats for fish, sequester carbon, trap sediment and provide shoreline protection ( [[#Ghermandi--2019|Ghermandi et al., 2019]] ). Climate change is compromising these ecosystem services ( ''medium confidence'' ). Marine heatwaves associated with ENSO events have triggered mass coral bleaching and mortality over the past 20 years ( [[#Oliver--2018|Oliver et al., 2018]] ). Mass coral bleaching in the western Indian Ocean occurred in 1998, 2005, 2010 and 2015/2016 with coral cover just 30–40% of 1998 levels by 2016 ( [[#Obura--2017|Obura et al., 2017]] ; [[#Moustahfid--2018|Moustahfid et al., 2018]] ). The northern Mozambique Channel has served as a refuge from climate change and biological reservoir for the entire coastal east African region ( [[#McClanahan--2014|McClanahan et al., 2014]] ; [[#Hoegh-Guldberg--2018|Hoegh-Guldberg et al., 2018]] ). A southern shift of mangrove species has been observed in south Africa ( [[#Peer--2018|Peer et al., 2018]] ) with loss in total suitable coastal habitats for mangroves and shifts in the distribution of some species of mangroves and a gain for others ( [[#Record--2013|Record et al., 2013]] ). Mangrove cover was reduced 48% in Mozambique in 2000 from Tropical Cyclone Eline, with 100% mortality of seaward mangroves dominated by ''Rhizophora mucronata'' ( [[#Macamo--2016|Macamo et al., 2016]] ). Recovery of mangrove species was observed 14 years later in sheltered sites. There is ''low confidence'' these cyclone-induced impacts are attributable to climate change owing, in part, to a lack of reliable long-term data sets ( [[#Macamo--2016|Macamo et al., 2016]] ). In west Africa, oil and gas extraction, deforestation, canalisation and de-silting of waterways have been the largest factors in mangrove destruction ( [[#Numbere--2019|Numbere, 2019]] ).

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