These changes have adverse impacts on both human and animal health, and the One Health movement acknowledges these inter-relationships. Most recently, the coronavirus disease 2019 (COVID-19) pandemic was characterised as a zoonotic infection and global pandemic, illustrating the dangers when viruses jump from animal to human populations.8 There has also been a growing interest in planetary health that focuses on the health and social effects of our ecological crisis as shown in Figure 2.9 We will use this framework to elaborate on the pathway from climate change to its health and social effects.
Proximate causes
The ecological crisis does not directly impact health but does so through several proximate causes. For example, many cities experience poor air quality with particulate pollution that impacts respiratory and cardiovascular diseases. Higher temperatures are associated with more allergens in the air.14 Food production is impacted by damage from weather events, drought, changes in pests and diseases, and even changes in the nutritional value of foods. Changes in weather impact the habitats of infectious disease vectors, such as mosquitoes, with an overall increase in communities at risk.
Change in temperature, precipitation patterns and extreme weather events directly affect the contamination of water sources, the efficacy of sanitation systems and the viability of hygiene behaviours.15 Increased temperatures trigger extreme rainfall events and floods which lead to loss and damage of infrastructure whilst driving poor water quality and lack of sanitation. Droughts can also reduce the amount of water available that then becomes polluted, also leading to an increase in water-borne diseases.16 Natural hazards themselves can have direct effects on people and their health services.
Mediating factors
Although climate change is global, countries and communities are not all equal in terms of their vulnerabilities and capacities to withstand the proximate causes.
In Africa, vulnerability arises from the interaction of environmental exposure and socioeconomic fragility. African countries are mostly low or middle-income countries with weaker infrastructure and limited resources. Africa’s vulnerability also stems from high dependence on climate-sensitive livelihoods (e.g. subsistence farming, pastoralism, informal sector jobs)17 and under-resourced health systems, particularly primary health care. The poorest and most marginalised groups, such as people living in informal settlements, migrants, rural smallholders, women, children and the elderly, face disproportionate exposure. Vulnerability is structurally embedded in poverty, infrastructure deficits and limited adaptive capacity.18 The region’s exposure to recurrent droughts, flooding, temperature variability and shifting rainfall patterns intersects with high burdens of infectious disease, widespread poverty, rapid population growth and climate-sensitive livelihoods.16 This creates a high baseline burden of infectious diseases coupled with emerging non-communicable diseases.
The health and related social effects of climate change
Vector-borne diseases (e.g. malaria, dengue, others)
Several reviews recommend urgent integration of climate information into vector control planning. Increased temperatures may increase transmission of vector-borne diseases in Africa, mostly in highland or fringe areas.19 Rising temperatures under climate scenarios affect vector ecology through temperature, rainfall and humidity. This contributes to shifting the distribution, seasonality and intensity of vector-induced diseases such as malaria and dengue. Several reviews and modelling studies indicate complex and location-specific impacts mostly in the tropical regions, whilst drought or extreme rainfall can either reduce or amplify risk depending on context and vector species.
Water-, sanitation- and hygiene-related diseases
Waterborne and hygiene-sensitive diseases constitute a major portion of the climate change burden in Africa. The Intergovernmental Panel on Climate Change (IPCC) and regional reviews link extreme hydrometeorological events with diarrhoeal disease burdens across Africa.1 Many communities rely on unimproved water sources. Although there may be various modifying factors, such as individual level of education, the impact of extreme weather events on water can amplify the risk of diseases such as gastroenteritis, cholera, typhoid fever and other enteric pathogens, mostly in urban informal settlements lacking piped water and sewage systems.20
Food security and malnutrition
Studies show that climate change through droughts, floods and shifting rainfall has severe impacts on crop yields, livelihoods, food safety and security, driving acute and chronic malnutrition.21 Food security refers to all stages of the food chain, production, processing, distribution and consumption to prevent health risk in food, whilst food safety refers to access to sufficient and nutritious food to meet people’s dietary needs and preferences. Both terms encompass availability, accessibility and stability of crop yields and food to combat mal- and undernutrition. Drought exacerbated by El Nino has produced large-scale food insecurity and child malnutrition in Africa, illustrating climate-driven poor health outcomes.21
Non-communicable diseases
Traditionally, health systems in Africa have focused on communicable diseases such as malaria, human immunodeficiency virus (HIV) and/or acquired immunodeficiency syndrome (AIDS) and tuberculosis. With climate change and air pollution playing a significant role in disease occurrence, Africa may undergo an epidemiological transition with a rapid rise of non-communicable diseases.14 The IPCC and Lancet Countdown emphasise the combined effects of heat and air pollution on morbidity and mortality.2 African urbanisation and reliance on biomass and coal energy have increased levels of coarse particulate matter (PM10) and fine (PM2.5) particulates in several countries. Dust storms worsen urban air pollution and are exacerbated by climate-related heat and drought.22 A study conducted in Cape Town, South Africa, demonstrated the interaction effect of climate-related extreme temperatures on air pollution and vice versa on respiratory and cardiovascular diseases.23 Heat stress increases heart rate, blood viscosity and risk of heart attacks and strokes, even insulin resistance and diabetes onset, especially in urban areas with high pollution.
Significant threats to maternal health and pregnancy outcomes are under recognised in most African countries. Pregnant women are especially vulnerable to impaired placental blood flow that contributes to adverse outcomes like pre-term birth and low birth weight, preeclampsia and hypertensive disorders.24 During pregnancy, heat stress, drought and dehydration can increase metabolic and cardiovascular demand that can trigger early labour and impair foetal growth.25
Mental health and climate change impacts
Throughout the entire African continent, climate shocks such as storms, droughts and extreme heat drive psychological distress. Due to social and economic constraints, the population experiences breakdowns in social support, as well as loss and damage to their livelihoods. Although the field of climate change and mental problems is not fully explored in Africa, the direct effects are thought to be related to immediate trauma and injury, and the indirect effects are through damage to the social foundation of society.26
A recent review of the mental health effects on adolescents and young adults found that extreme weather events can be associated with depression, acute stress, post-traumatic stress disorder, substance use, suicide risk and anxiety disorders. Emotional responses to climate change include sadness, suicidal ideation, ecological grief and loss of one’s identity.27
Migration, vulnerability and climate change impacts
Migration refers to internally displaced people (IDP), migrants (people moving from one country to another), refugees (legally recognised migrants in the country of host) and asylum seekers (not yet legally recognised as a refugee in the country of destination).28 Their movements are not only driven by socioeconomic push and pull factors. Environmental factors such as extreme weather events (droughts, floods, cyclones, heatwaves) alter their livelihoods or force people to seek a better life elsewhere.29 But they often remain vulnerable when their movements are accompanied with overcrowding, inadequate water, sanitation and hygiene.30 Poor-quality water supplies in camps or informal settlements lead to rapid spread of water-borne diseases such as cholera or diarrhoea. Overcrowded and poor shelters can easily trigger respiratory diseases such as asthma and chronic obstructive pulmonary disease (COPD). Most migrants and IDP experience significant but under-recognised and under-assessed mental health issues such as anxiety, depression and PTSD.31 They face physical violence from the host country, which often underlines tension over job competition, housing and services between migrants and local people. Women and children are the most affected in these events, with limited antenatal care and inadequate nutrition.31 All these health risks are often aggravated when migrants and IDP are denied access to healthcare services (barriers to medication and interruption of chronic care, for diabetes, hypertension and HIV) in the host country.30
Conflict, injury and trauma
Several studies state that climate change is increasingly recognised not only as an environmental and health threat, but also as a risk multiplier that can escalate social tensions, contribute to violent conflict and increase injury and trauma. When governance is weak, climate change can increase competition over scarce water and grazing land and lead to economic instability and loss of livelihoods with migration and local tensions.32 Populations may compete for grazing land and water with conflict between farming and pastoralist communities. Extreme weather events can directly or indirectly cause injury, trauma, domestic violence, interpersonal aggression and death.33 Climate change-induced wildfires are directly associated with burns and smoke inhalation. Floods can lead directly to drowning and physical injury. Heatwaves can contribute directly to heatstroke and cardiovascular injury.3 Drought can trigger loss and damage of livestock, food insecurity and increased recruitment into violent groups, particularly in pastoralist regions.34
Health effects of vulnerable health facilities and services
Increased vulnerability of healthcare facilities and services has compromised the ability of the health system to respond to communities’ health emergencies. In most National Adaptation Plans for climate change risks, the health sector and its infrastructure are considered a vulnerable sector.35 The healthcare sector and services are facing increased stress related to the intensified impacts of climate change on health infrastructure. For example, Mozambique recently reported that 472 health facilities had been destroyed since 2019.36 Extreme weather events can destroy hospitals and clinics, prevent healthcare workers from getting to work and damage medical equipment. This results in reducing, disrupting and delaying emergency response capacity. After disasters from floods, cyclones, heatwaves, wildfires or drought, increased morbidity and mortality often result from interruption of healthcare services.37 This is particularly visible at the primary care level which has become not only highly sensitive to climate shocks, but also the frontline of defence against the health impacts of climate change.38 Primary care facilities are the foundation of health systems, especially in low- and middle-income countries. When infrastructure is damaged or inaccessible due to climate shocks, routine and continued healthcare stops or is disrupted.37 This can generate long-term health consequences beyond the immediate disaster, and contribute to increased workload and burnout for healthcare workers.