11.1  Climate change impacts on human health

Climate change can impact human health in many different ways, both positively and negatively. The positive health impacts of climate change are the benefits to health that may arise from a warmer climate. For example, warmer winters may result in fewer deaths resulting from exposure to cold weather; also the geographical range of some disease ‘vectors’, like mosquitoes, may contract if extreme hot weather conditions dry out the shallow water collections they require for their breeding cycle. Vectors are insects such as mosquitoes, flies and other animals (for example snails, rats and dogs) that transmit disease-causing agents such as bacteria and viruses from one host to another. Overall, however, many scientists think that the negative health impacts of climate change are expected to exceed the positive health impacts (Confalonieri et al., 2007).

The health impacts of climate change can be direct or indirect. The direct health impacts occur when climate changes in the temperature, precipitation and weather extremes affect our health and survival directly. For example, very hot weather can cause heat-related illness such as heat exhaustion and heat stroke; and floods can cause injury and drowning. These direct effects are predicted to increase as the rate of climate change increases in the future. You should be able to recall the effects of extreme weather events from Study Session 10.

The indirect health impacts of climate change are health problems caused by changes in natural and social systems as a result of shifts in the climate, which in turn have adverse effects on human health. Changes to social and ecological systems can allow disease to spread more easily, or cause disease to emerge in areas where previously it was unknown or only present at low levels (Senay and Verdin, 2005; Gage et al., 2008). For instance, 40 years ago you would not find a single case of malaria in the highlands of Ethiopia, but today outbreaks of malaria in the Ethiopian highlands are common. This is because climate change has increased the night-time temperatures in the highlands, allowing malaria-infected mosquitos to live at altitudes where previously they could not survive the cold nights. Longer periods of warm weather have created favourable conditions for mosquitoes to breed and these changes in the highland climate have led indirectly to outbreaks of malaria occurring for the first time (Abeku et al., 2004; Pascual et al., 2006).

  • Study Session 10 stated that an increase in flooding leads to higher frequency of diarrhoeal diseases. Can you explain how flooding resulting from climate change can indirectly have this effect on human health?

  • Flood water washes animal and human waste from latrines and open defecation into rivers, lakes, ponds and wells where people obtain their drinking water. It may also destroy water treatment facilities and breaks water pipes, allowing waterborne diarrhoea-causing organisms to spread through the water resources in rural and urban areas.

Climate change is expected to increase the frequency of waterborne and food-borne infectious diseases in countries like Ethiopia because of the inadequate supply of safe drinking water, low sanitation coverage and poor hygiene practices (Kovats et al., 2003; Confalonieri et al., 2007). For example, following the 2006 flood in many parts of the country there were outbreaks of acute watery diarrhoea among people in Gambela Region, West Arsi Zone, Oromia Region, Addis Ababa and very remote places like Guji Zone (International Federation of Red Cross and Red Crescent Societies, 2005). Acute watery diarrhoea is a symptom of many faecal–oral diseases including cholera.

  • What are faecal–oral diseases? Can you name any other examples that occur in Ethiopia?

  • Faecal-oral diseases occur when pathogenic organisms from faeces are transmitted from person to person via the oral route (mouth), for example when contaminated hands or utensils (cups, spoons) touch the mouth, or infected food or water is swallowed. Faecal–oral diseases include cholera, giardiasis, typhoid and dysentery, among others.

As you learned in Study Session 1, Ethiopia is already classified by the United Nations as water stressed, meaning that the availability of water is less than 1700 m3 per person per year. If climate change reduces the amount of accessible water to less than 1000 m3 per person per year, Ethiopia will be in the ‘water scarce’ category. Water stress and water scarcity increase the risk of water-washed diseases, which occur as a result of poor personal hygiene and inadequate washing. Examples of water-washed diseases include the infectious eye diseases trachoma and conjunctivitis, and scabies caused by tiny mites that burrow into the skin.

Malnutrition among children aged under 5 is another widespread problem in Ethiopia, and one which could become more prevalent if climate change leads indirectly to food shortages. As Study Session 10 described, more frequent or more severe droughts reduce food production because crops fail and livestock die (Abaya et al., 2011). Malnutrition, malaria and diarrhoeal diseases are particularly related to the increased frequency and intensity of floods and droughts in Ethiopia, as you can see in Table11.1.

Table 11.1  Climate change impacts on human health. (Few, 2007)
Health problemFloodDrought
Faecal-oral, waterborne and water-washed diseases

Contamination of the home and living environment

Disruption of water and sanitation facilities

Shortage of water for hygiene and food preparation; use of untreated water sources; inadequate sanitation
Vector-borne diseases Altered breeding conditions for mosquitoes; rodents taking refuge in housesAltered breeding conditions for mosquitoes; human population movements
MalnutritionCrop damage and loss of subsistence food; disruption of food supplies; disruption of livelihood/incomeLoss of subsistence food or income; regional food shortages; use of nutrient-deficient alternative foods

Learning Outcomes for Study Session 11

11.2  Climate change impacts on the environment