Summary: Increases are likely in heat stress mortality (particularly in Australia), tropical vector-borne diseases such as dengue, and urban pollution-related respiratory problems. These impacts are small compared to the total burden of ill-health, but they have the potential to cause significant community impact and cost. Indigenous communities and economically disadvantaged persons appear to be more at risk. Adaptation responses include strengthening existing public health infrastructure and meeting the needs of vulnerable groups. A moderate degree of vulnerability is apparent with health.
Average life expectancy in Australia and New Zealand is relatively high, and access to medical care is relatively good by international standards. There are considerable inequalities in health status and access to services, however. Disadvantaged groups such as indigenous peoples and the poor are likely to be most at risk from the effects of climate change.
In parts of urban Australia, the frequency of very hot days (over 40°C) is expected to increase by 50-100% for a 2°C increase in mean temperature (Hennessy and Pittock, 1995). This is likely to lead to an increase in deaths, especially in cities such as Melbourne that are subject to wide variability in temperature, but insufficient information is available at present to quantify this impact. There may be fewer deaths in winter with warmer temperatures. For example, the winter excess in coronary heart disease mortality in Australia and New Zealand appears to be related in part to ambient temperature (Enquselassie et al., 1993). However, studies in other parts of the world suggest that reduced mortality from cold extremes would probably only partly offset the heat stress effect (IPCC 1996, WG II, Section 18.2.1).
In both Australia and New Zealand, there are significant food- and waterborne diseases that occur more commonly in warmer conditions (IPCC 1996, WG II, Section 18.3.5). For example, in parts of Australia, an amoeba that causes meningoencephalitis proliferates in water pipes that are heated in summer as the water travels overland (IPCC 1996, WG II, Section 18.3.2). Hotter weather also will exacerbate urban air pollution due to photochemical oxidants (Woodward et al., 1995), possibly leading in the major cities (Sydney, Melbourne, Auckland) to increased frequency of respiratory problems and deaths (IPCC 1996, WG II, Section 18.3.5). Australia and New Zealand have rates of asthma and other allergic conditions that are higher than elsewhere in the Pacific or in many parts of Europe, and these diseases may be exacerbated by warmer and more humid climates (Pearce et al., 1993).
Any increase in extreme events and flooding, including those associated with sea-level rise, would increase deaths, injury, infectious diseases, and psychological disorders and may increase road accidents. Other waterborne illnesses-such as viral, bacterial, and protozoal diarrhoea and cyanobacterial poisoning-would be affected by any changes in water availability (due to flooding, droughts, and public water shortages). Some disease vectors also are influenced by changes in water availability. New Zealand currently is free of human arbovirus infections (i.e., viruses borne by arthropods-ticks, mites, etc.), but if temperature and rainfall alter it may become susceptible to infections that currently are common in Australia (Weinstein et al., 1995). Vectors for dengue and malaria already exist in Australia, and southward expansion of the vector populations with temperature increases would increase the potential for insect-borne diseases to become more widely established. These diseases are very sensitive to climate variability-for example, outbreaks of dengue are much more common in the western Pacific islands during relatively warm and wet La Niņa years (Hales et al., 1996).
Conditions forecast under climate change could alter the distribution and proliferation of arthropod vectors and/or natural vertebrate hosts. Warmer and wetter conditions would lead to increased incidences of insect-borne infections such as Japanese Encephalitis virus, Murray Valley Encephalitis virus, Ross River virus, and dengue. In southeastern Australia, epidemics of Murray Valley Encephalitis and Ross River virus infection follow heavy rain in the Murray-Darling basin (Nicholls, 1986; IPCC 1996, WG II, Section 18.104.22.168), so additional cases might be expected if the frequency or duration of heavy rainfall events increased. However, the relationship between climate, vector distribution, and disease are complex. For example, although the incidence of infection with Ross River virus may increase with increased rainfall, the incidence of symptomatic disease may actually fall because individuals who are infected as children remain asymptomatic and are immune for life.
The indigenous peoples of Australia and New Zealand-Australian Aborigines, Torres Strait Islanders, and Maori-may be more vulnerable to climate change because their health status in general is worse than for other Australians (Australian Bureau of Statistics, 1997) and other New Zealanders (Pomare et al., 1995). These health status differences result largely from social and economic disadvantage, which itself is a cause for susceptibility. For example, many Australian Aborigines live in remote areas, in poor housing, and are particularly susceptible to infections related to deficiencies in water supply and sewage disposal (Moss, 1994). Under some scenarios, these conditions could worsen due to higher temperatures, changes in rainfall, higher water tables, and rising sea levels. Reduced freshwater supply, increased standing water, or both could increase exposure to microbial and viral infections and vector-borne diseases (Kolsky, 1993; Hales et al., 1995; Henderson et al., 1995; Jacobson and Graham, 1996).
The health impacts of climate change will include economic and social costs. These costs are difficult to quantify, but the evidence suggests that the health impacts for the region are likely to be relatively small compared to impacts from other diseases and sources of mortality. At the same time, it should be cautioned that there is considerable uncertainty in our current knowledge of not only the likely direct impacts but also the complexities of social responses to change and interaction with other sectors. For example, there could be changes in the incidence of zoonoses (vertebrate animal-mediated diseases) such as leptospirosis, a concern in New Zealand, as farming systems and zoonoses transmission alter in response to climate change. Heat stress impacts will be affected by housing choices and changing attitudes to air conditioning. More difficult to estimate precisely-but possibly of greater importance to public health in the long term-are the indirect effects of climate change, such as any adverse social and economic effects, especially on vulnerable groups, arising from impacts on other sectors and any large population shifts of "environmental refugees" (for example, from Pacific atolls) (Moore and Smith, 1996).
Major adaptation responses include strengthening the existing public health infrastructure (such as disease monitoring, vector management, and primary health care); improving protective systems where deficiencies are apparent already (for example, comprehensive infectious disease surveillance and border quarantine controls to reduce introduction of exotic pathogens); and meeting the needs of the most vulnerable groups in the population who will be at greatest risk from new climate-related threats to health (Woodward, 1996), including through improvements in water supply and sewerage systems (Moss, 1994). Adaptations to deal with the indirect socioeconomic effects arising in other sectors may require significant policy responses at the national and international levels.
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