Climate change has the potential to impact on any health outcome that is seasonal and associated with weather and climate variations. In addition, many key determinants of human health, such as food and freshwater availability, are strongly influenced by weather and climate. Climate-sensitive health outcomes include injuries, illnesses, and deaths associated with extreme weather events, and the effects of changing weather patterns surface through ecological systems, such as water- and food-borne diseases, vector-borne and respiratory diseases associated with ground-level ozone and aeroallergens, and under-nutrition. Climate change also may result in resource depletion and other processes that could lead to large-scale migration, with associated health impacts. While negative health effects are projected for all countries, the largest impacts are expected in lower-income populations, primarily those living in tropical and subtropical countries.
INFECTIOUS DISEASES: Climate is a primary determinant of transmission of a range of infectious diseases. Increasing temperatures could effect vector and rodent-borne diseases, in terms of the density of insects and rodents in a particular area. Expansion in range can expose new populations, who have little or no immunity to new infections, which could result in wide-scale disease outbreaks. Although understanding of the potential impact of climate change on infectious diseases is still in its relatively early stages, expert assessments have concluded that climate change is expected to be among the most important drivers of infectious disease in the future. A UK review/study considered scenarios for the next 10-25 years of infectious diseases in humans, animals, and plants for the UK and sub-Saharan Africa, aiming to produce a vision of new systems needed for disease detection, identification and monitoring.
Malaria is the most important vector-borne disease in the world; it is also a preventable disease. About 40 per cent of the world's population is at risk of contracting malaria, and roughly 75 per cent of the cases occur in Africa, with the remainder occurring in Southeast Asia, the western Pacific, and the Americas. In sub-Saharan Africa, malaria remains the most common parasitic disease and is the main cause of morbidity and mortality among children less than five years of age, and among pregnant women. There has been a great deal of interest in modelling how the incidence and geographic range of malaria could change under different climate change projections. Results from several models suggest that climate change could alter the season of transmission and geographic range of malaria in Africa, particularly sub-Saharan Africa.
Studies have shown that some areas in Asia are projected to be at increased risk of malaria, while reductions have been projected for some areas in Central America and around the Amazon, due to decreases in rainfall. An assessment of Australia based on climatic suitability for the main Anopheline vectors projected a likely southward expansion of habitats, although the future risk for 'endemic proportions' would remain low due to the capacity to respond. Climate change could have impact on the incidence and geographic range of a large number of vector-borne diseases including dengue fever, Lyme disease, plague, Chagas disease and Rift valley fever.
AIR POLLUTION: In some regions, climate change may increase concentrations of selected air pollutants, particularly ozone, and could decrease concentration of other pollutants, such as particulate matter (due to increasing heavy precipitation events). There is an extensive literature documenting the adverse health impacts of exposure to elevated concentrations of air pollutants. More is known about the potential impacts of climate change on ground-level ozone than on other air pollutants. Acute exposure to elevated concentrations of ozone is associated with increased hospital admissions for pneumonia, chronic obstructive pulmonary disease, asthma, allergic rhinitis and other respiratory diseases, and with premature mortality.
Changes in concentrations of ground-level ozone are driven by scenarios of future emissions and/or weather patterns have been projected for Europe and North America, with most projections suggesting increasing concentrations. Higher ozone concentrations are likely to increase a range of health problems and increase premature mortality in susceptible individuals. Despite the heavier pollution burdens, no studies have been conducted for cities in low- or middle-income countries.
MALNUTRITION: Climate change threatens human health through its effecting under-nutrition and food insecurity. About 800 million people are undernourished, causing over 15 per cent of the total global disease burden, and over three billion people are micronutrient-deficient. The prevalence of undernourishment has fallen over the recent decades, with reductions in Asia and Latin America partly offset by increases in Africa and the Middle East. Almost 60 per cent of the world's undernourished people live in South Asia, while the highest incidence of undernourishment is in Sub-Saharan Africa, where more than one-third of the population is underfed.
It has been found in a recent study that half of the world's population could face severe food shortages by the end of this century, as rising temperatures take their toll on farmers' crops; a greater proportion of this will be in Africa. Harvests of staple food crops such as rice and maize could fall by between 20 per cent and 40 per cent in the tropical and sub-tropical countries. Although data are limited, malnutrition associated with drought and flooding may be one of the important consequences of climate change due to the large number of people that may be affected.
EXTREME WEATHER EVENTS: The adverse health consequences of flooding and windstorms often are complex and include the physical health effects experienced during the extreme weather events. They are also associated with mental health effects, such as post-traumatic stress disorder, resulting from the experience of the event or from the recovery process. These psychological effects tend to be much longer-lasting and may be worse than the direct physical impacts. More than 90 per cent of the disasters that occurred in 2007 were the result of extreme weather, together accounting for 95 per cent of the reported fatalities and 80 per cent of the total USD 82 billion economic losses. The health impacts of extreme events in low- and middle-income countries are substantially larger.
Projections suggest that regions affected by moderate droughts are set to double by the end of the century, with areas affected by extreme droughts increasing from 1 per cent today to 30 per cent in 2100. The loss of livelihoods due to drought is a major trigger for population displacements that may cause additional adverse health burdens. The effects of drought on health include malnutrition (protein-energy malnutrition and/or micronutrient deficiencies), infectious and diarrhoeal diseases and respiratory diseases. Droughts, especially in rural areas, have a tendency to influence migration into cities, increasing urbanisation and stressing the socio-economic conditions already affected by high levels of city population growth. Prolonged droughts fuel fires, releasing respiratory pollutants, while floods can create mosquito breeding sites, foster fungal growth, and flush microbes, nutrients and chemicals into bays and estuaries, causing water-borne disease outbreaks from organisms.
The most comprehensive evaluation of the health burden due to climate change uses a comparative risk assessment approach to estimate total health burdens from climate change, and to project how much of this burden might be avoided by stabilising greenhouse gas emission. The health outcomes (diarrhoea, malaria, malnutrition, heat-related mortality, and injury from floods and landslides) are chosen based on sensitivity to climate variations. The relative risks attributable to climate change vary by health outcomes and regions, with the majority of the health burdens set to increase due to rise in diarrhoeal diseases and malnutrition, primarily in low-income populations. The actual health burdens depend on assumptions of population growth, future baseline disease incidence, and the extent of adaptation. We need to improve our knowledge of designing, implementing and monitoring effective and efficient adaptation options when it comes to climate change.
The writer is a development communications consultant and researcher. [email protected]
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