Climate impacts are determined not just by the magnitude of environmental change but also by the vulnerability of exposed populations. Examples of biophysical vulnerability are the susceptibility of pale-skinned populations to the effects of UV radiation and the vulnerability of isolated island ecosystems such as New Zealand's to invasion by exotic species (including disease vectors). Another example is infections spread to humans from animals, such as cryptosporidiosis. New Zealand has relatively high rates of notified cases of this infection (Russell et al., 1998). This may be related to the conjunction of high densities of livestock and unprotected human drinking water supplies. In such a setting, increased rainfall intensity would promote transmission of the pathogen (by washing animal excreta containing the organism into the water supply).
Woodward et al. (1998) reviewed social determinants of vulnerability to health effects of climate change in the Pacific region. Australia and New Zealand are two of the wealthiest countries in the region, with relatively low population densities and well-developed social services. For these reasons, Australia and New Zealand are likely to be less vulnerable overall to many of the threats to health from climate change than neighboring countries. However, within both countries there are groups that are particularly susceptible to poor health. Sources of disadvantage include poverty, low housing standards, high-risk water supplies, lack of accessible health care, and lack of mobility. These factors tend to be concentrated in particular geographical locations and ethnic groups (Crampton and Davis, 1998) and carry with them increased vulnerability to most of the hazards that are associated with climate variability and climate change.
There have been no studies in New Zealand or Australia that have attempted to quantify vulnerability to disease and injury. Some work has been carried out on indices of environmental vulnerability (e.g., Kaly et al., 1999). These studies have focused on measures of the resilience and integrity of ecosystems; with further development, they may assist in future forecasts of the impacts of climate change on human health.
There is no opportunity to study directly, in a conventional controlled fashion, the effects on health of climate change. Research to date in Australia and New Zealand has concentrated on the association of climate variability, at relatively restricted spatial and temporal scales, with the incidence of disease. It is not simple to extrapolate from these findings to long-term climate change. This problem is not particular to Australia and New Zealand, but there are informative local examples in the literature. These include analyses of roles of climate-related variables other than temperature (e.g., the critical effects of wind on air pollution, rainfall density on mosquito breeding, and humidity on heat stress); interactions with local ecosystems (e.g., the potential for amplification of certain arboviruses in New Zealand wildlife); and human behaviors that influence exposures (such as changing patterns of skin protection and the implications for UV exposures) (Hill et al. 1993; Russell, 1998b).
A major challenge in Australia and New Zealand is how to protect and improve public health systems that deal with threats to health such as those that will potentially accompany climate change. Examples include border controls to prevent introduction of pathogens (including those from livestock and animal imports), measures required to ensure safe food and clean water, and primary health care services that reach the most disadvantaged and vulnerable members of the community. Threats to these systems include restrictions on government spending, increasing demands, and fragmented systems of purchase and provision of services.
With vector-borne diseases, the major challenge in Australia will be to control the expansion and spread of diseases that already are present in the country, such as Ross River virus and Murray Valley encephalitiswhich are strongly influenced by climatic events. Introduction of new pathogens from close neighbors such as Papua New Guinea also is possible. Imported Japanese encephalitis and malaria remain serious threats, influenced principally by the numbers of people moving across the Torres Strait and the effectiveness of health services in the far north of Australia.
In New Zealand, the key issue for the health sector is how to prevent the introduction of vector-borne disease, particularly arboviruses carried by mosquitoes. Competent vectors for conditions such as Ross River virus and dengue have been detected frequently at entry points in recent years. This is likely to be a result of increasing trade and passenger traffic between New Zealand and other countries, as well as heightened awareness and better reporting. Eradication programs are expensive, and they are feasible only when the spread of exotic mosquitoes is confined. With repeated incursions and/or dispersion, the emphasis is likely to shift to control strategies.
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