Climate observations and models broadly agree that – on a global level – extreme weather events are likely to occur more frequently and/or with greater intensity as the twenty-first century progresses (Niang et al., 2014). Extreme weather will clearly have an impact on the way we live our lives. This section considers some aspects of how people living across the African continent might be affected by extreme weather events.
5.1 Human health and heat exposure
Heat affects human health, mainly because exposure to extreme heat can exacerbate underlying health problems. Deaths can and do occur following periods of extreme heat, and while many people can cope with one single day of extreme temperatures, mortality rates increase during prolonged heatwave events that last for more than two days. The greatest health problems are during extended periods of extreme heat, when temperatures during the night and the day are high, because there is then no period for humans to recover or recuperate (Perkins, 2015).
The human body thermoregulates to maintain core temperature at typically 36.5 ℃–37.5 ℃. A wet-bulb temperature of 35 °C marks the upper physiological limit for human survival (Raymond et al., 2020). Overheating can lead to hyperthermia. Typically, overheating happens with fever but also if the external temperature is hot for a long period and the body is not able to cool down. A core body temperature of 38 ℃ is considered high and if it reaches 40 ℃ it becomes life threatening (NHS, 2020). If ambient temperature is more than 37 ℃ then the body will accumulate heat and is likely to become hyperthermic. Sweating to dissipate heat becomes ineffective at high relative humidity, which means that in high humidity even a lower ambient temperature can be deadly (Mora et al., 2017). Analysis of the combined effect of temperature and humidity on human health found that the high mortality rates in India and Pakistan during separate extreme heat events in 2015 were because of the combination of high temperatures and high humidity, a situation compounded because hospitals were over-capacity with patients suffering from heat-related illness (Wehner et al., 2016).
Heat-related health impacts can include increased morbidity through ischemic heart disease, ischemic stroke, cardiac dysrhythmia, dehydration, acute renal failure, heat illness, diarrhoea and heat stroke (Hopp et al., 2018). A loss of productivity is anticipated with sustained periods of heat particularly if combined with high humidity (Levy et al., 2016; Perkins-Kirkpatrick & Gibson, 2017).
Extreme heat events are known to cause heat-related deaths – the death toll from the European-wide heatwave in 2003 reached tens of thousands and peaked in France, Germany and Italy (Christidis et al., 2014; Mora et al., 2017).
Studies analysing exposure to extreme temperatures found that extreme heat events generally cause excess mortality within a few days. By contrast, extreme cold weather events cause excess mortality over a longer period of up to 25 days. Susceptibility to extreme weather events is influenced by factors including: the ability of a person to acclimatise, age, socioeconomic conditions, whether the setting is urban or rural and access to air conditioning (Anderson & Bell, 2009). High excess human morbidity and mortality rates are associated more with sustained periods of moderate temperatures rather than one-off very hot days (Gasparrini et al. 2015; Perkins-Kirkpatrick & Gibson, 2017).
5.1.1 Human survival in a hot and humid future
Humans have adapted to live within a broad temperature range of between 4 ℃ and 35 ℃. However, research has found that since the mid-Holocene (6,000 years before the present day) a majority of humans have chosen to live in regions with an average annual temperature of ∼11 ℃ to 15 ℃ (Xu et al., 2020).
Global climate modelling projects that under a high-emissions, business-as-usual worst-case-scenario (the RCP8.5*SSP3 scenario), by 2070, the global mean human-experienced temperature increase will be 7.5 ℃ compared to the pre-industrial period (Xu et al., 2020). Not every continent will experience a surface temperature rise of such magnitude, but the modelling projection incorporates population growth under socioeconomic pathway 3 (SSP3), and population growth is projected to increase faster in hotter regions, which affects the projected mean temperature rise experienced by people. (For an explanation of the IPCC’s Representative Concentration Pathways (RCP) and why this scenario has attracted controversy, see section 7.0.) The worst-case scenario projection, using the RCP8.5*SSP3 scenario and not allowing for migration, is that 3.5 billion people globally will be living in regions with a mean annual temperature of around or exceeding 29 ℃, which could be regarded as being or verging on being uninhabitable. So, a region with a mean annual temperature of 13 ℃ in 2020 might experience a mean annual temperature of 20 ℃ in 2070 – such as the climate presently found in Northern Africa. But even if greenhouse emissions are on a downward trajectory towards net zero in 2100 – the RCP2.6 scenario – the projections are that by 2070 around 2.6 billion people around the globe could be displaced due to inhospitable ambient temperatures.
The map in Fig. 4 shows projected ‘niche displacement’ of people affected by land suitability for human habitation in 2070, modelled under RCP8.5 and with population changes under the SSP3 scenario. If the majority of humans continue to live in regions with mean annual temperatures of around 11 ℃–15 ℃, as has historically been the case, then the projection is that some regions of the world will become less suitable for humans and other regions will become more suitable. If the human population is distributed according to the mean annual temperature, then in 2070 the projection is that the trend in human migration will be from the regions on the map shaded red to those shaded green. If the RCP8.5*SSP3 projections are accurate (that is, that greenhouse gas emissions continue on a business-as-usual basis through the twenty-first century), regions of the Sahel, Southern Africa and East Africa could experience huge decreases in land suitable for human habitation by the last decades of the twenty-first century (Xu et al., 2020).
Anthropogenic climate change means that many regions of the world are predicted to experience average annual temperatures that are higher than those at present. Mean annual temperature is of relevance because as the global climate becomes hotter, some regions – including parts of the Sahel – may become too hot for human habitation. The number of people affected will depend upon the extent to which the global climate warms compared to preindustrial temperature observations – there is a big difference between the number of people impacted by a 2 ℃ average global temperature increase in comparison to a 1.5 ℃ increase. Even so, limiting the global average temperature rise to no more than 2 ℃ above pre-industrial levels is still not likely to prevent an increase in the frequency and intensity of extreme heat events (Diffenbaugh & Scherer, 2011). Some climate models predict mass migration of people away from regions that become too hot for human habitation, such as parts of Northern and Central Africa (Xu et al., 2020). Such widespread movement could lead to further cultural and political tensions within and beyond the regions worst affected. See also section 5.6.
Research suggests that urbanisation can compound problems such as flood risk and heat exposure because cities commonly lack both green spaces to absorb rainfall and trees to provide shade. Urbanisation along coastlines may create particular problems for communities, which may then experience and have to cope with storm surges and coastal erosion, as well as more widespread structural problems such as poor sanitation (Lwasa et al., 2018; Okaka & Odhiambo, 2019; Rohat et al., 2019). Problems can often be disproportionately felt in the poorest communities whose residents tend to live in slums and shanties in the city margins. These may be particularly susceptible to flooding and also lack access to air conditioning or adequate shade. Rapid urbanisation coupled with land-use change and deforestation exacerbates the problems of a warming climate on local residents (Orimoloye et al., 2019), expanding the phenomenon of the ‘urban heat island’ into adjoining areas even less able to cope.
5.3 Food and water security
Agriculture is the largest single economic activity in Africa, accounting for around 60% of employment and, in some countries, more than 50% of gross domestic product (Collier et al., 2008). Agriculture in Africa is generally negatively impacted by extreme temperature events because many crops are already grown at the limits of their thermal tolerance and resistance to water stress. Moreover, a large proportion of agricultural production in Africa occurs in semi-arid regions, which are projected to become drier in the future (Scholes et al., 2015).
The World Meteorological Organisation notes in ‘State of the Climate in Africa 2019’ (WMO, 2020) that in facing a mix of increased temperatures, changing precipitation patterns, rising sea levels and more frequent extreme weather and climate events, there are also key risks to agriculture, which forms the backbone of national economies. Reduced crop productivity as a result of heat and drought stress, increased pest, disease and flood damage will result in serious adverse effects on food security and on livelihoods at regional, national and household levels. The World Meteorological Organisation (WMO, 2020) also states that under RCP8.5, reductions in mean yield of 13% are projected in West and Central Africa, 11% in Northern Africa and 8% in East and Southern Africa. Rice and wheat are predicted to be the most severely affected crops with millet and sorghum the least affected.
Climate changes are likely to impact food production. The IPCC reported in its Fifth Assessment Report (AR5) that measures to improve the resilience of food production have improved since AR4, but that the mitigation factors used currently will not be adequate in the long-term (Niang et al., 2014). Agroecological farming and agroforestry are being adopted in Africa and are helping to improve resilience to the changing climate, but the effectiveness of adaptation strategies depends upon factors including funding and technical support (Niang et al., 2014). For example, Guba is an organisation based in Eswatini, Southern Africa, that runs training courses in organic, sustainable and ecological farming (www.gubaswaziland.org).
Global climate change is likely to affect seasonal weather patterns. Concerns are that conversion of Africa’s dry tropical forests and savannahs to croplands for food production will threaten the natural carbon stores in those biomes.
Extreme heat events – as well as droughts, floods and landslides – can impact livelihood activities such as farming and crop harvests (Orimoloye et al., 2019). A study that used 20,000 historical maize trials in Africa, combined with daily weather data, found that productivity of African maize decreased by 1% for every 1 ℃ warming above 30. In drought conditions the yield dropped by 1.7% under the same temperature conditions (Lobell et al., 2011). Food prices are expected to increase significantly, making the affordability of food a growing challenge for many African communities (Scholes et al., 2015).
Increased ambient temperature and changes to rainfall patterns may affect water availability. Water shortages may lead to food insecurity if water shortage and drought decrease crop yields and affect livestock. Limited access to safe drinking water, or damage to sanitation infrastructure, increases the risk of contracting diseases such as cholera or leishmaniasis (Niang et al., 2014; Cambaza et al., 2019). Extreme rainfall and flooding has been associated with outbreaks of diarrhoea (Levy et al., 2016).
5.4 Locust swarms
Throughout 2020, huge locust swarms, comprising millions of insects and covering many square miles, have been devastating crops across East Africa, as well as in countries further afield including Yemen, Iran, Pakistan and India. The Horn of Africa, notably Kenya, Ethiopia and Somalia, has been particularly badly affected this year. The swarms are the worst in Kenya for 70 years. The origin of the 2019–2020 upsurge can be traced back to specific climate conditions that favoured insect breeding. Tropical cyclones over the Arabian Peninsula in May 2018 and again in October the same year brought rains and favourable breeding conditions for locusts, which began swarming in January 2019 over Yemen and Saudi Arabia, reaching Somalia and Ethiopia from mid-2019 onwards. The swarms have continued to develop through 2020, affecting Somalia, Ethiopia, Kenya, Uganda, Sudan and Tanzania, bringing widespread devastation to areas already coping with a mix of floods and drought, and associated threats to food security (Salih et al., 2020; FAO, 2020).
Some reports in the scientific literature suggest that anthropogenic climate changes – such as increased temperature and rainfall over desert regions – contributed to the environmental conditions that lead to plagues of locusts (Meynard et al., 2020). However, attributing the current 2019–2020 locust swarm entirely to anthropogenic climate change is challenging because so many other factors are also involved. For example, Salih et al. (2020) suggest that pest control measures have been impacted by underfunding and financial constraints associated with the ongoing Covid-19 pandemic, thereby exacerbating the particularly devastating swarms seen this year.
There is much debate in the scientific literature concerning the connection between violent conflict and weather extremes, with no overall consensus. For example, a study that analysed the records of violent conflicts in East Africa from 1991 to 2009 found no statistically significant relationship between precipitation anomalies and conflict in that region, but indicated that higher-than-normal temperatures increased the risk of violence (O’Loughlin et al., 2012). Another study, based on analysis of events in sub-Saharan Africa between 1980 and 2012, also suggested a link between temperature extremes and human conflict (O’Loughlin et al., 2014). The latter study found that colder temperatures have no effect on the risk of conflict, moderate temperatures reduce the risk of conflict (a reduction of 12%) and very hot temperatures increase the risk of violent events by 26.6% in comparison to the number of events during normal temperatures.
Overexploitation of natural resources coupled with climate change is expected to increase the risk of violent conflict (Niang et al., 2014). Tension and conflict could arise in the event of mass migration of people moving away from areas that begin to suffer the impact of extreme events such as heatwaves, flooding or drought (Matthews et al., 2017; Xu et al., 2020).
Others have discussed situations in which climate change may not be a direct cause of human–human conflict but the changing climate conditions can exacerbate volatile situations or can indirectly cause conflict, particularly in regions that do not have strong state support mechanisms. A recent report (ICRC, 2020) highlights tensions in the Central African Republic in which changing patterns of transhumance, the country’s existing armed conflict, and access to resources such as water for livestock and for growing crops are being exacerbated by the changing climate such as increasing drought conditions. The situation is significant because 70% of the Central African Republic population rely on subsistence agriculture. Interruptions to the agricultural system could impact food security of those communities that rely on them, which extend beyond the borders of the Central African Republic.
Before making projections of the extent to which biodiversity might be impacted by extreme weather events and by climate change, it is useful to first understand that Africa’s ecosystems have been and continue to be shaped by water, fire and mega-herbivores (animals with a body mass greater than 1,000kg, such as elephants and rhinoceros) as well as climate (Midgley & Bond, 2015). Plants and animals have adapted in different regions to scarcity or abundance of water supply, fire hinders tree growth in the savannah and mega-herbivores consume vast quantities of plant matter and return nutrients to the soil.
Climate change-driven alterations in rainfall patterns and temperature, and the changing concentration of global atmospheric CO2 are highly likely to drive changes in terrestrial ecosystems (Niang et al., 2014, section 188.8.131.52), and is a significant threat to endemic species across the African continent (Malcolm et al., 2006).
A modelling study assessing the possible impact of climate change on biodiversity suggested that South Africa’s Cape Floral region (which has 5,682 endemic plant species and 53 endemic vertebrates) is particularly vulnerable to habitat loss under climate change. All climate modelling scenarios projected the extinction of more than 100 species and some modelling scenarios projected the extinction of more than 2,000 plant species from the Cape Floral region under doubled atmospheric CO2 conditions in comparison to current baseline levels (Malcolm et al., 2006). Other regions of the continent are also projected to experience species extinction in a warming global climate. The estimated extinction of Afroalpine species endemic to the Bale Mountains of south-central Ethiopia under a scenario of 2 ℃ warming falls in the range 3.5–8.7% or 5–11 species; under both 3 ℃ and 4 ℃ of climate heating the estimated extinction range is 36-57% or 41–65 species (Kidane et al., 2019).
Some researchers suggest that future projections of vegetation structure and biodiversity in Africa are difficult to make without fully understanding how ecosystems will respond to disturbance and atmospheric CO2. There is also the view that while some individual species will adapt to changing conditions, widespread changes to a habitat could lead to extinctions of endemic species (Malcolm et al., 2006).
Rainfall and temperature extremes are highly likely to impact biodiversity, but because of limited observational data, scientists are uncertain about the extent to which climate change could affect the availability and quality of freshwater in the future (Niang et al., 2014, section 22.3.3). The availability of water is a key driver in African ecosystems, perhaps more so than temperature. Lack of observational data means that it is difficult to determine trends in relation to species abundance or distribution of species in response to climate changes (Midgley & Thuiller, 2011).
5.7 Impacts on economic well-being
Climate change is not a problem of Africa’s making, yet parts of Africa may be particularly negatively affected because of their geography, agricultural dependence and difficulties in adapting to changing weather patterns (Collier et al., 2008). Africa’s economies are vulnerable to change, as illustrated by the work of Matyas & Silva (2013), which shows how rainfall patterns drive changes to the income of communities living in central and northern Mozambique. The study by Matyas & Silva (2013) also highlights the paradox of how damaging cyclones can also bring some positive effects on the economic position of households, either through beneficial rainfall or employment from reconstruction building work. A key point to note in relation to the aftermath of extreme weather events is that economic consequences will vary considerably depending upon the response made by individual countries.
Although households may have considerable experience of coping with temporary shocks, such defensive flexibility has not, to date, been combined with sustained ability to adapt to new circumstances or adopt new technologies (Collier et al., 2008). This suggests that there is great value in analysing weather and socio-economic data together to better understand patterns of vulnerability and potential responses to extreme weather events.
Future research that builds upon studies such as that by Matyas & Silva (2013), and others, will be important to help determine the relationship between extreme weather events and socio-economic well-being of African communities.