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 the 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, 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).

Climate change is expected to increase the frequency of waterborne and food-borne infectious diseases in low-income countries 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 floods, outbreaks of acute watery diarrhoea among people are very common. Acute watery diarrhoea is a symptom of many faecal–oral diseases including cholera.

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 low-income countries 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, as you can see in Table 11.1.

Table 11.1 Climate change impacts on human health. (Few, 2007)