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

==== 9.8.2.1 Observed Impacts and Projected Risks for Staple Crops ====

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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]] ).

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[[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.

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