The Third Assessment Report of the IPCC (IPCC 2001) estimates that globally the average land and sea surface temperature has increased by 0.60±0.2°C since the mid-19th century, with much of the change occurring since 1976. Of the many impacts of climate change, those on human health are often placed amongst the most worrying. The impacts of climate change on human health are many and complex. GHG emissions can in principle be considered as risk factor that could potentially be altered by human intervention, with associated effects on the burden of disease.
The increase in the frequency and intensity of extreme temperatures have direct and indirect effects on health. Direct effects include thermal stresses (cardio-vascular and respiratory diseases, heat exhaustion, heat cramps and dehydration), while indirect effects are related to the impact of heat extremes on urban air pollution and humidity (which can aggravate pre-existing morbidity).
Extreme temperatures tends to aggravate pre-existing respiratory and cardio-vascular diseases. In the recent years, extreme weather events, such as floods and landslides, storms, cyclones and droughts, have caused considerable damage and loss of life in China, Venezuela, Bangladesh and Mozambique. Direct impacts of extreme weather events include increased incidence of deaths, physical injuries and psychological stresses, while indirect impacts are related to increased risk of exposure to water-borne diseases due to water contamination, and impacts on malnutrition due to loss in agricultural production. Unsafe water and sanitation conditions and decrease water accessibility would further increase the transmission of infectious diseases (Markandya and Chiabai.,2009).
Climate change also leads to outbreak of water-borne diseases, with cholera and diarrhoea being potentially most problematic(McMichael et al., 2006) The Intergovernmental Panel on Climate Change (IPCC) has declared with “very high confidence” that climate change already contributes to the global burden of disease (Confalonieri et al., 2007).
Human health is heavily dependent on clean water resources and adequate sanitation. According to the WHO, diarrhoea is the disease most attributable to quality of the local environment. It is estimated that 88% of diarrhoea cases result from the combination of unsafe drinking water, inadequate sanitation, and improper hygiene (WHO 2006, Pruss-Ustun 2006). Environmental factors account for an estimated 94% of the global disease burden for diarrhoea (WHO 2006), which is a leading cause of death among children. One of the main sources of diarrheal disease is contamination by faecal-oral pathogens that are largely caused by a lack of safe drinking water and sanitation facilities. Additionally, inadequate sanitation poses threats to the environment from improper disposal and treatment of human waste. It is important for populations to have access to drinking water and adequate sanitation because these factors play large roles in human health.
The IPCC summarized the main health impacts as follows:
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Increases in malnutrition and consequent disorders, with implications for child growth and development
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Increased death, disease and injury due to heat waves, floods, storms, fires and droughts
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Increased burden of diarrhoeal diseases
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Increased frequency of cardio-respiratory diseases due to higher concentrations of ground level ozone related to climate change
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Altered spatial distribution of some infectious disease vectors.
According to Haines et al(2006) research studies on the health impacts of climate change addresses three main topics- current associations between climate and disease; the effect of recent changes in climate; and the evidence base for projecting the future impacts of climate change on health.
The impact of climate change on human health vary greatly depending on many variables including the behaviour, age, gender, race, and economic status of individuals. Moreover, such variables can also be expanded to include region, the sensitivity of populations, the extent and length of exposure to climate change, and society’s ability to adapt to change. People living in small islands and coastal regions, megacities, and mountainous and polar regions are particularly prone to such degrading environmental conditions. McMichael et al (2000) inferred that the effects of global climate change are predicted to be heavily concentrated in poorer populations at low latitudes, where the most important climate-sensitive health outcomes (malnutrition, diarrhoea and malaria) are already common, and where vulnerability to climate effects is greatest affecting mostly the younger age groups.
Likewise, children living in poor countries, the elderly, and those with infirmities or pre-existing medical conditions will be affected most sensitively by these alterations.
Figure 1 gives us an overview of the impacts of climate change on human health and what sort of mitigation and adaptive measures are required to resolve the problem.
Figure 1. Impacts of climate change on human health
Though different studies have tried to address the impacts of climate change on human health but as per IPCC(2014) there lies important research gaps regarding the health consequences of climate change and co-benefits actions, particularly in low-income countries.
Human health therefore figures prominently in assessments of the impacts of climate change. The welfare costs (or benefits) of health impacts contribute substantially to the total costs of climate change (Cline, 1992; Fankhauser, 1995; Tol, 2002). The majority of estimates of the economic damages of global warming rely on the methodology of direct costs, that is, damage equals price times quantity. In case of human health, the price is typically equal to the value of a statistical life, which is based on estimates of the willingness to pay to reduce the risk of death or diseases, or the willingness to accept compensation for increased risk (Viscusi and Aldy, 2003).