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

==== 12.4.1.1 Heat and Cold ====

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'''Mean air temperature:''' The African continent has experienced increased warming since the beginning of the 20th century in regions where measurements allow a sufficient homogeneous observation coverage to estimate trends ( ''high confidence'' ) (Figure Atlas.11). This warming is ''very likely'' attributable to human influence ( [[IPCC:Wg1:Chapter:Chapter-3|Chapter 3]] and Atlas.4.2) at continental scale. Mean annual temperatures have increased at a high rate since the mid-20th century, reaching 0.2°C–0.5°C per decade in some regions such as north, north-eastern, west and south-western Africa (high confidence) (Atlas.4.2 and Figure Atlas.11).

It is ''very likely'' that temperatures will increase in all future emissions scenarios and all regions of Africa (Atlas.4.4). By the end of the century under RCP8.5 or SSP5-8.5, all African regions will ''very likely'' experience a warming larger than 3°C except Central Africa, where warming is ''very likely'' expected above 2.5°C, while under RCP2.6 or SSP1-2.6, the warming remains ''very likely'' limited to below 2°C (Figure Atlas.12). A ''very likely'' warming with ranges between 0.5°C and 2.5°C is projected by the mid-century for all scenarios depending on the region ( ''high confidence'' ). Mean temperatures for all regions are projected to increase with increasing global warming ( ''virtually certain'' ) (Figure Atlas.12).

'''Extreme heat:''' Warm extremes have increased in most of the regions ( ''high confidence'' ), NEAF, SEAF and MDG ( ''medium confidence'' ) and with ''low confidence'' in CAF (Table 11.4). Despite the increasing mean temperature, there is ''low confidence'' ( ''limited evidence'' ) that Africa has experienced increased extreme heat stress trend for agriculture or human health in the last two decades of the 20th century in a few regions such as West Africa, South Africa and North Africa considering the period from 1973 to 2012 ( [[#Knutson--2016|Knutson and Ploshay, 2016]] ).

A substantial increase in heatwave magnitude and frequency over most of the Africa domain is projected for even 2°C global warming ( ''high confidence'' ) (Sections 11.3 and 11.9, and Table 11.4), with potential effects on health and agriculture. The number of days with maximum temperature exceeding 35°C is projected to increase ( [[#Coppola--2021b|Coppola et al., 2021b]] ) in the range of 50–100 days by 2050 under SSP5-8.5 in WAF, ESAF and WSAF and NEAF ( ''high confidence'' ) (Figure 12.4b). Under SSP1-2.6, the change in the number of exceedance days remains limited to about 40–50 days per year at the end of the century in these regions, while it increases by 150 days or more in WAF, CAF for SSP5-8.5 (Figure 12.4a,c; Figure 12.SM.1).

Mortality-related heat stress levels and deadly temperatures are ''very'' ''likely'' to become more frequent in the future in RCP8.5/SSP5-8.5 and RCP4.5/SSP2-4.5 and for a 2°C global warming ( [[#Mora--2017|Mora et al., 2017]] ; [[#Nangombe--2018|Nangombe et al., 2018]] ; [[#Sylla--2018a|Sylla et al., 2018a]] ; [[#Rohat--2019|Rohat et al., 2019]] ; Q. [[#Sun--2019|]] [[#Sun--2019|]] [[#Sun--2019|Sun et al., 2019]] ). In particular the equatorial regions where heat is combined with higher humidity levels, but also North Africa, the Sahel and Southern Africa (Figure 12.4d–f) are among the regions with the largest increases of heat stress ( [[#Zhao--2015|Zhao et al., 2015]] ; [[#Ahmadalipour--2018|Ahmadalipour and Moradkhani, 2018]] ; [[#Coffel--2018|Coffel et al., 2018]] ). Mitigation scenarios make a large difference in frequency of exceedance of high heat stress indices thresholds (e.g., HI &gt; 41°C) by the end of the century (Figure 12.4d–f; [[#Schwingshackl--2021|Schwingshackl et al., 2021]] ). In West Africa and Central Africa, under SSP5-8.5, the expected number of days per year with HI &gt; 41°C will increase by around 200 days while in SSP1-2.6 such exceedances are expected to increase by less than 50 days per year (Figure 12.4; Figure 12.SM.2).

'''Cold spell and frost:''' Africa experiences cold events and frost days that can affect agriculture, infrastructure, health and ecosystems, especially in Southern and North Africa, which have marked cold seasons and mountainous areas. Cold spells have ''likely'' decreased in frequency over subtropical areas. In particular, in North and Southern Africa, the frequency of cold events has ''likely'' decreased in the last few decades (Sections 11.3 and 11.9). There is a ''high confidence'' that cold spells and low target temperatures will decrease in future climates under all scenarios in West, Central and East Africa. Heating degree days will have a substantial decrease by the end of the century for up to about one month under RCP8.5 in North and Southern Africa ( ''high confidence'' ) ( [[#Coppola--2021b|Coppola et al., 2021b]] ).

'''There is''' high confidence '''that extreme heat has increased in frequency and intensity in most African regions. Heatwaves and deadly heat stress and the frequency of exceedance of hot temperature thresholds (e.g., 35°C) will drastically increase by the end of the century''' ( high confidence ''') under SSP5-8.5, but limited increases are expected in SSP1-2.6. Dangerous heat stress thresholds (HI &gt; 41°C) are projected to be crossed more than 200 days more in West and Central Africa under SSP5-8.5, while this increase remains limited to a few tens of days more for SSP1-2.6. Cold spells and frost days are projected to occur less frequently in all scenarios.'''

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[[File:ec270bb71e166b03dbc08e4cca546973 IPCC_AR6_WGI_Figure_12_5.png]]

'''Figure 12.5''' '''|''' '''Projected changes in selected climatic impact-driver indices for Africa.''' Mean change in 1-in-100-year river discharge per unit catchment area (Q100, m <sup>3</sup> s <sup>–1</sup> km <sup>–2</sup> ) from CORDEX-Africa models for 2041–2060 relative to 1995–2014 for RCP8.5. '''(b)''' Shoreline position change along sandy coasts by the year 2100 relative to 2010 for RCP8.5 (metres; negative values indicate shoreline retreat) from the CMIP5-based dataset presented by [[#Vousdoukas--2020b|Vousdoukas et al. (2020b)]] . '''(c)''' Bar plots for Q100 (m <sup>3</sup> s <sup>–1</sup> km <sup>–2</sup> ) averaged over land areas for the AR6 WGI Reference Regions (defined in Chapter 1). The left-hand column within each panel (associated with the left-hand y-axis) shows the ‘recent past’ (1995–2014) Q100 absolute values in grey shades. The other columns (associated with the right-hand y-axis) show the Q100 changes relative to the recent past values for two time periods (‘mid’ 2041–2060 and ‘long’ 2081–2100) and for three global warming levels (GWLs, defined relative to the pre-industrial period 1850–1900): 1.5°C (purple), 2°C (yellow) and 4°C (brown). The bars show the median (dots) and the 10–90th percentile range of model ensemble values across each model ensemble. CMIP6 is shown by the darkest colours, CMIP5 by medium, and CORDEX by light. SSP5-8.5/RCP8.5 is shown in red and SSP1-2.6/RCP2.6 in blue. '''(d)''' Bar plots for shoreline position change show CMIP5-based projections of shoreline position change along sandy coasts for 2050 and 2100 relative to 2010 for RCP8.5 (red) and RCP4.5 (blue) from [[#Vousdoukas--2020b|Vousdoukas et al. (2020b)]] . Dots indicate regional mean change estimates and bars show the 5–95th percentile range of associated uncertainty. Note that these shoreline position change projections assume that there are no additional sediment sinks/sources or any physical barriers to shoreline retreat. See Technical ( [[IPCC:Wg1:Chapter:Annex-vi|Annex VI]] for details of indices. Further details on data sources and processing are available in the chapter data table (Table 12.SM.1).

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