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

=== 9.8.2 Observed Impacts and Projected Risks to Crops and Livestock ===

<div id="h2-30-siblings" class="h2-siblings"></div>

<div id="9.8.2.1" class="h3-container"></div>

<span id="observed-impacts-and-projected-risks-for-staple-crops"></span>
==== 9.8.2.1 Observed Impacts and Projected Risks for Staple Crops ====

<div id="h3-46-siblings" class="h3-siblings"></div>

Climate change is already negatively impacting crop production and slowing productivity growth in Africa ( ''high confidence'' ) ( [[#Iizumi--2018|Iizumi et al., 2018]] ; [[#Ray--2019|Ray et al., 2019]] ; [[#Sultan--2019|Sultan et al., 2019]] ; [[#Ortiz-Bobea--2021|Ortiz-Bobea et al., 2021]] ). Climate change has reduced total agricultural productivity growth in Africa by 34% since 1961, more than in any other region ( [[#Ortiz-Bobea--2021|Ortiz-Bobea et al., 2021]] ). Maize yields have decreased 5.8% and wheat yields 2.3%, on average, in sub-Saharan Africa due to climate change in the period 1974–2008 ( [[#Ray--2019|Ray et al., 2019]] ). Overall, climate change has decreased total food calories across all crops in sub-Saharan Africa by 1.4% on average compared to a no climate change counterfactual since 1970, with up to 10% reductions in Ghana and Zimbabwe ( [[#Ray--2019|Ray et al., 2019]] ).

Farmers perceive a wide variety of climate threats to crop production including droughts, precipitation variability, a delayed onset and overall reductions in early growing season rainfall and excess heat ( [[#Rankoana--2016a|Rankoana, 2016a]] ; [[#Elum--2017|Elum et al., 2017]] ; [[#Kichamu--2017|Kichamu et al., 2017]] ; [[#Alvar-Beltrán--2020|Alvar-Beltrán et al., 2020]] ). Farmers attribute these perceived changes as a major driver of yield losses ( [[#Ayanlade--2016|Ayanlade and Jegede, 2016]] ; see [[#9.4.5|Section 9.4.5]] ). Over half of surveyed farmers in west Africa perceive increases in crop pests and diseases as due to climate change as the range and seasonality of many pests and diseases change under warming ( [[#Callo-Concha--2018|Callo-Concha, 2018]] ). Pests and diseases contribute between 10–35% yield losses for wheat, rice, maize, potato and soybean in sub-Saharan Africa ( [[#Savary--2019|Savary et al., 2019]] ). Recent locust outbreaks in 2019 in east Africa have been linked to climate conditions caused in part by ocean warming ( [[#Wang--2020b|Wang et al., 2020b]] ; see Box 5.8).

Future climate change may increase insect pest-driven losses in Africa for maize, rice and wheat. Compared to 1950–2000, losses may increase by up to 50% at 2°C of global warming ( [[#Deutsch--2018|Deutsch et al., 2018]] ). However, many challenges remain in modelling pest and disease under climate change with additional research needed expanding the range of crops and diseases studied ( [[#Newbery--2016|Newbery et al., 2016]] ).

Agriculture in Africa is especially vulnerable to future climate change in part because 90–95% of African food production is rainfed ( [[#Adams--2018|Adams, 2018]] ). Maize, rice, wheat and soybean yields in tropical regions (20°S–20°N) are projected to decrease approximately 5% per degree Celsius of global warming in a multi-model ensemble ( [[#Rosenzweig--2014|Rosenzweig et al., 2014]] ; [[#Franke--2020|Franke et al., 2020]] ). Dryland agricultural areas are especially sensitive to changes in rainfall. For example, without adaptation, substantial yield declines are projected for staple crops in north Africa. A recent meta-analysis of 56 studies indicates that, compared to 1995–2005, economic welfare in the agriculture sector in north Africa is projected to decline 5% for 2°C global warming and 20% for 3°C global warming, and in sub-Saharan Africa by 5% (2°C) and 10% (3°C) ( [[#Moore--2017a|Moore et al., 2017a]] ), both more pessimistic than previous economic estimates.

A synthesis of projected staple crop impacts across 35 studies for nearly 1040 locations and cases shows, on average, decreases in crop yields with increasing global warming across staple crops in Africa, including when accounting for CO 2 increases and adaptation measures. For example, for maize in west Africa, compared to 2005 yield levels, median projected yields decrease 9% at 1.5°C global warming and 41% at 4°C, without adaptation (Figure 9.22). However, uncertainties in projected impacts across crops and regions are driven by uncertainties in crop responses to increasing CO 2 and adaptation response, especially for maize in east Africa and wheat in north Africa and east Africa (Figure 9.22; [[#Hasegawa--2021|Hasegawa et al., 2021]] ).

<div id="_idContainer071" class="Figure"></div>

[[File:0f438802e215429c53faa1822d1831d7 IPCC_AR6_WGII_Figure_9_022.png]]

'''Figure 9.22 |''' '''Projected yield changes for major staple crops in Africa due to climate change (compared to 2005 yield levels).''' Projected impacts are grouped by projected global warming levels. Boxplots show a synthesis of projected staple crop impacts, with and without adaptation measures (e.g., planting date, cultivar, tillage or irrigation). On average crop yields are projected to decrease with increasing global warming across staple crops in Africa. The overall adaptation potential to offset yield losses across Africa for rice, maize and wheat reduces with increasing global warming. On average, in projections including adaptation options, yield losses in the median case are reduced from −33% to −10% of 2005 levels at 2°C of global warming and from −46% to −23% at 4°C. Global warming levels were calculated using a baseline for pre-industrial global mean temperature of 1850–1900. Data are a synthesis across 35 studies for nearly 1040 locations and cases of projected impacts for regions of Africa for maize, rice and wheat ( [[#Hasegawa--2021|Hasegawa et al., 2021]] ; Table SM9.5).

There is also growing evidence that climate change is ''likely'' beginning to outpace adaptation in agricultural systems in parts of Africa ( [[#Rippke--2016|Rippke et al., 2016]] ). For example, despite the use of adjusted sowing dates and existing heat-tolerant varieties, Sudan’s domestic production share of wheat may decrease from 16.0% to 4.5–12.2% by 2050 under RCP8.5 (2.4°C global warming) ( [[#Iizumi--2021|Iizumi et al., 2021]] ).

Elevated CO 2 concentrations in the atmosphere might mitigate some or all climate-driven losses ( [[#Swann--2016|Swann et al., 2016]] ; [[#Durand--2018|Durand et al., 2018]] ), but there is considerable uncertainty around the CO 2 response ( [[#Deryng--2016|Deryng et al., 2016]] ; [[#Toreti--2020|Toreti et al., 2020]] ), especially when nutrients such as nitrogen and phosphorus are limiting crop growth. Additional Free-Air Carbon dioxide Enrichment (FACE) experiments are needed in the tropics, particularly on the African continent, to better understand the impacts of increased CO 2 concentrations on the productivity of crops and cultivars grown in Africa under additional temperature impacts and water and nutrient limitations ( [[#Ainsworth--2021|Ainsworth and Long, 2021]] ). Warming and elevated CO 2 may also change the nutritional content of some crops. By 2050 under RCP8.5 (2.4°C global warming), overall wheat yields and grain protein content may decrease by 10% and 15%, respectively, in north and east Africa, and by over 15% in southern Africa ( [[#Asseng--2019|Asseng et al., 2019]] ). See [[IPCC:Wg2:Chapter:Chapter-5|Chapter 5]] for more details on CO 2 impacts and uncertainties.

<div id="9.8.2.2" class="h3-container"></div>

<span id="observed-impacts-and-projected-risks-on-regional-cash-crops-and-food-crops"></span>
==== 9.8.2.2 Observed Impacts and Projected Risks on Regional Cash Crops and Food Crops ====

<div id="h3-47-siblings" class="h3-siblings"></div>

Few studies have attributed changes in yields of cash crops and other regionally important food crops in Africa to human-caused climate change, but recent research suggests yields of cash crops in Africa have already been impacted by climate change, in both a negative and positive manner ( [[#Falco--2012|Falco et al., 2012]] ; [[#Traore--2013|Traore et al., 2013]] ; [[#Ray--2019|Ray et al., 2019]] ). For example, between the period 1974–2008, sugarcane yields decreased on average by 3.9% and 5.1% in sub-Saharan Africa and north Africa, respectively, due to climate change, while sorghum yields increased 0.7%, and cassava yield increased 1.7% in sub-Saharan Africa and 18% in north Africa ( [[#Ray--2019|Ray et al., 2019]] ).

There are also limited studies assessing projected climate change impacts on important cash crops and food crops other than maize, rice and wheat ( [[#Jarvis--2012|Jarvis et al., 2012]] ; [[#Schroth--2016|Schroth et al., 2016]] ; [[#Awoye--2017|Awoye et al., 2017]] ). These studies often represent changes at specific sites in a country or assess changes in the yield and/or suitability for cultivating a specific crop across a larger geographic area. Climate change is projected to have overall positive impacts on sugarcane and Bambara nuts in southern Africa, oil palm in Nigeria and chickpea in Ethiopia ( ''low confidence'' ) (Figure 9.23).

<div id="_idContainer073" class="Figure"></div>

[[File:4783493b4ddb04ea2e1d89f35619e11a IPCC_AR6_WGII_Figure_9_023.png]]

'''Figure 9.23 |''' '''Projected risks at increasing global warming levels for regionally important cash and food crops in Africa.''' Insufficient data indicates there were limited to no published studies that have quantified projected climate change impacts or adaptation options for specific crops under different warming levels (see Table SM9.6). Global warming levels were calculated using a baseline for pre-industrial global mean temperature of 1850–1900.

Climate change is projected to reduce sorghum yields in west Africa (Figure 9.23). For example, across the west African Sahel savanna sorghum yields are projected to decline on average 2% at 1.5°C and 5% at 2°C global warming ( [[#Faye--2018|Faye et al., 2018]] ). For coffee and tea in eastern Africa, olives in Algeria and sunflower in Botswana and Morocco, studies indicate mostly negative impacts on production systems. For example, in Kenya, compared to 2000, optimal habitat for tea production is projected to decrease in area by 27% with yields declining 10% for global warming of 1.8–1.9°C, although yield declines may be reduced at higher levels of warming ( [[#Beringer--2020|Beringer et al., 2020]] ; [[#Jayasinghe--2020|Jayasinghe and Kumar, 2020]] ; [[#Rigden--2020|Rigden et al., 2020]] ). Suitable area for tea production may reduce by half in Uganda ( [[#Eitzinger--2011|Eitzinger et al., 2011]] ; [[#Läderach--2013|Läderach et al., 2013]] ). In east Africa, the coffee-growing area is projected to shift up in elevation with suitability decreasing 10–30% between 1.5–2°C of global warming ( [[#Bunn--2015|Bunn et al., 2015]] ; [[#Ovalle-Rivera--2015|Ovalle-Rivera et al., 2015]] ).

For all other crops, there is at least one study that finds low to highly negative impacts for one or several warming levels (Figure 9.23). Mixed results on the direction of change often occur when several contrasting sites with varying baseline climates are studied, and when a study considers the full range of climate scenarios. For example, there are mixed results on the direction of change for impacts of 1.5°C global warming on cassava, cotton, cocoa and millet in west Africa ( ''low confidence'' ) (Figure 9.23). In general, there is limited evidence in the direction of change, due to single studies being available for most crop-country combinations ( [[#Knox--2010|Knox et al., 2010]] ; [[#Chemura--2013|Chemura et al., 2013]] ; [[#Asaminew--2017|Asaminew et al., 2017]] ; [[#Bouregaa--2019|Bouregaa, 2019]] ). Occasionally, two studies agree on the direction and magnitude of change, for example, for potatoes in east Africa, yields are projected to decrease by 11–17% with 3°C of warming ( [[#Fleisher--2010|Fleisher et al., 2010]] ; [[#Tatsumi--2011|Tatsumi et al., 2011]] ).

<div id="9.8.2.3" class="h3-container"></div>

<span id="observed-impacts-and-projected-risks-for-wild-harvested-food"></span>
==== 9.8.2.3 Observed Impacts and Projected Risks for Wild-Harvested Food ====

<div id="h3-48-siblings" class="h3-siblings"></div>

Wild-harvested foods (e.g., fruits, vegetables and insects) provide dietary diversification and for many people in Africa, wild-harvested food plants may provide a livelihood and/or nutritional safety net when other sources of food fail, such as during drought ( [[#Sunderland--2013|Sunderland et al., 2013]] ; [[#Shumsky--2014|Shumsky et al., 2014]] ; [[#Wunder--2014|Wunder et al., 2014]] ; [[#Baudron--2019b|Baudron et al., 2019b]] ). In Zimbabwe, during lean times, consumption of wild fruits increases, as does their sale to generate income for additional food expenses in poor, rural households (Mithöfer and Waibel, 2004). In Mali, Tanzania and Zambia, household surveys indicate that forest products including wild foods can play an important role in reducing household vulnerability to climate shocks by providing alternative sources of food and income during droughts and floods ( [[#Robledo--2012|Robledo et al., 2012]] ). In the parklands of west Africa, wild trees are a significant source of wild foods and are thus a place where one might expect wild plant foods to make an important contribution to diets and nutrition ( [[#Boedecker--2014|Boedecker et al., 2014]] ; [[#Leßmeister--2015|Leßmeister et al., 2015]] ). Non-timber forest products are consumed by an estimated 43% of all households in Burkina Faso ( [[#FAO--2019|FAO, 2019]] ), and wild vegetables accounted for about 50% of total vegetable consumption in southeastern Burkina Faso ( [[#Mertz--2001|Mertz et al., 2001]] ).

The focus of projected climate change impacts has been almost exclusively on agricultural production, yet climate change could have substantial impacts on the distribution and availability of wild-harvested food plants in Africa ( [[#Wessels--2021|Wessels et al., 2021]] ). Non-cultivated species in Africa are vulnerable to current and future climate changes, with widespread changes in woody plant cover already observed (see [[#9.6.1.1|Section 9.6.1.1]] ). Evidence about the impacts of climate change on individual wild food species is less consistent. Communities in the Kalahari ( [[#Crate--2016|Crate and Nuttall, 2016]] ) and Zimbabwe ( [[#Sango--2015|Sango and Godwell, 2015]] ) report growing scarcity of wild foods (such as wild meat and fruit) perceived to be, at least in part, due to drought and climate change. Shea tree ( ''Vitellaria paradoxa'' ) nuts provide fats and oils for the diets of many rural populations in west Africa. In Burkina Faso, global warming of 3°C is projected to reduce area of suitable habitat for the shea tree by 14% ( [[#Dimobe--2020|Dimobe et al., 2020]] ). In southern Africa, 40% of native, wild-harvested food plant species are projected to decrease in geographic range extent at 1.7°C global warming with range reductions for 66% of species projected for 3.5°C ( [[#Wessels--2021|Wessels et al., 2021]] ).

<div id="9.8.2.4" class="h3-container"></div>

<span id="observed-impacts-and-projected-risks-on-livestock"></span>
==== 9.8.2.4 Observed Impacts and Projected Risks on Livestock ====

<div id="h3-49-siblings" class="h3-siblings"></div>

Livestock systems in Africa are already being affected by changes in climate through increased precipitation variability leading to decreasing fodder availability ( [[#Sloat--2018|Sloat et al., 2018]] ; [[#Stanimirova--2019|Stanimirova et al., 2019]] ). More than twice as many countries in Africa have experienced increases in precipitation variability in the last century than decreases ( [[#Sloat--2018|Sloat et al., 2018]] ). Fodder availability is also being impacted by woody plant encroachment—the increase in shrub and tree cover—which has increased by 10% on subsistence grazing lands and 20% on economically important grazing lands in south Africa in the last 60 years ( [[#Stevens--2016|Stevens et al., 2016]] ), and is driven in part by climatic factors (see [[#9.6.1.1|Section 9.6.1.1]] ). Increased temperature and precipitation have contributed to the expanding range, especially in east and southern Africa, of several ixodid tick species which carry economically important livestock diseases ( [[#Nyangiwe--2018|Nyangiwe et al., 2018]] ).

Pastoralists in Africa perceive the climate as already changing and report more erratic and reduced rainfall, prolonged and more frequent droughts and a rise in temperature ( [[#Sanogo--2017|Sanogo et al., 2017]] ; [[#Kimaro--2018|Kimaro et al., 2018]] ). They also report reduced milk production, increased deaths and disease outbreaks in their herds due to malnutrition and starvation resulting from the shortages in forage and water ( [[#Kimaro--2018|Kimaro et al., 2018]] ). Additional research is required to attribute precipitation variability to human-induced climate change (see [[#9.5|Section 9.5]] ), and to evaluate the relative contributions of climate change and management to disease vector extent.

Future climate change will have compounding impacts on livestock, including negative impacts on fodder availability and quality, availability of drinking water, direct heat stress and the prevalence of livestock diseases ( [[#Nardone--2010|Nardone et al., 2010]] ; [[#Rojas-Downing--2017|Rojas-Downing et al., 2017]] ; [[#Godde--2021|Godde et al., 2021]] ). Climate change is projected to negatively affect fodder availability ( [[#Briske--2017|Briske, 2017]] ) because overall rangeland net primary productivity (NPP) by 2050 is projected to decrease 42% under RCP4.5 (2°C global warming) and 46% under RCP8.5 (2.4°C global warming) for western sub-Saharan Africa, compared to a 2000 baseline ( [[#Boone--2018|Boone et al., 2018]] ). NPP is also projected to decline by 37% in southern Africa, 32% in north Africa and 5% in both east Africa and central Africa by 2050 under RCP8.5 (2.4°C global warming) ( [[#Boone--2018|Boone et al., 2018]] ). For example, in Zimbabwe by 2040–2070, net revenues from livestock production, compared to a 2011 survey, are projected to decline by 8–32% under RCP4.5 for 2°C and 11–43% under RCP8.5 for 2.7°C global warming due to a decline in fodder availability ( [[#Descheemaeker--2018|Descheemaeker et al., 2018]] ). The available literature does not comprehensively capture the economic implications of climate-related impacts on livestock production across Africa.

Fodder quality, critical for animal health and weight gain, is at risk from climate change as increases in temperature, elevated CO 2 and water stress have been shown to reduce dry matter digestibility and nitrogen content for C 3 grasses ( [[#Augustine--2018|Augustine et al., 2018]] ), tropical C 4 grasses ( [[#Habermann--2019|Habermann et al., 2019]] ) and fodder crops such as Lucerne/Alfalfa ( [[#Polley--2013|Polley et al., 2013]] ; [[#Thivierge--2016|Thivierge et al., 2016]] ).

Climate change is projected to threaten water availability for livestock. Droughts in Africa have become more intense, frequent and widespread in the last 50 years ( [[#Masih--2014|Masih et al., 2014]] ), and progressive increase in droughts between 3- and 20-fold under climate change up to 3°C of warming are projected for most of Africa ( [[#9.5|Section 9.5]] ). In the Klela basin in Mali by 2050, groundwater recharge is projected to decline by 49% and groundwater storage by 24% under RCP8.5 (2.4°C global warming) compared to the 2006 baseline ( [[#Toure--2017|Toure et al., 2017]] ). Water availability for livestock during drought is a major concern for many African pastoralists including but not limited to those in Zimbabwe ( [[#Dzavo--2019|Dzavo et al., 2019]] ) and Nigeria ( [[#Ayanlade--2019|Ayanlade and Ojebisi, 2019]] ). Increased livestock mortality and livestock price shocks have been associated with droughts in Africa, as well as being a potential pathway for climate-related conflict ( [[#Catley--2014|Catley et al., 2014]] ; see Box 9.9; [[#Maystadt--2014|Maystadt and Ecker, 2014]] ).

Heat stress may already be the largest factor impacting livestock production in many regions in Africa ( [[#El-Tarabany--2017|El-Tarabany et al., 2017]] ; [[#Pragna--2018|Pragna et al., 2018]] ), as the combination of high temperatures and high relative humidity can be dangerous for livestock and has already decreased dairy production in Tunisia ( [[#Amamou--2018|Amamou et al., 2018]] ). Climate change is projected to increase heat stress for all types of livestock, especially in the tropics (Figure 9.24; [[#Lallo--2018|Lallo et al., 2018]] ). More studies quantifying the impact of heat stress on other types of livestock production loss are needed in Africa ( [[#Rahimi--2021|Rahimi et al., 2021]] ).

<div id="_idContainer075" class="Figure"></div>

[[File:f05a4c8929a6a6a995c432f95aaae706 IPCC_AR6_WGII_Figure_9_024.png]]

'''Figure 9.24 |''' '''Severe heat stress duration for cattle in Africa is projected to increase with increasing global warming.'''

'''(a)''' Number of days per year with severe heat stress in the historical climate (1985–2014).

'''(b)''' Historical cattle exposure to severe heat. Cattle density data from [[#Gilbert--2018|Gilbert et al. (2018)]] .

'''(c, d)''' Projected increase in the number of days per year with severe heat stress for a global warming level of 1.5°C and 3.75°C. Severe heat stress for cattle is projected to become much more extensive in the future in Africa at increased global warming levels. Strong mitigation would substantially limit the spatial extent and the duration of cattle heat stress across Africa. Heat stress is estimated using the Temperature Humidity Index with a value greater than 79 considered the onset of severe heat stress (Livestock Weather Safety Index) ( [[#Lallo--2018|Lallo et al., 2018]] ). Global warming of 1.5°C used scenario SSP1–2.6 and global warming of 3.75°C used SSP5-8.5, both for 2070–2099 (12 climate models from [[#O’Neill--2016|O’Neill et al., 2016]] ; [[#Tebaldi--2021|Tebaldi et al., 2021]] ). Global warming levels were calculated using a baseline for pre-industrial global mean temperature of 1850–1900.

Climate change will impact livestock disease prevalence primarily through changes in vector dynamics or range ( [[#Abdela--2016|Abdela and Jilo, 2016]] ; [[#Semenza--2018|Semenza and Suk, 2018]] ). African Rift Valley Fever (RVF) and trypanosomiasis are positively associated with extreme climate events (droughts and ENSO) ( [[#Bett--2017|Bett et al., 2017]] ) and are projected to expand in range under climate change ( [[#Kimaro--2017|Kimaro et al., 2017]] ; [[#Mweya--2017|Mweya et al., 2017]] ). More quantitative estimates of projected risk from diseases are needed.

<div id="9.8.3" class="h2-container"></div>

<span id="adapting-to-climate-variability-and-change-in-agriculture"></span>