Chapter 4 Climate Impacts and Responses

Impacts of Climate Change on Australia > Disease and human health

Climate change can affect human health directly through, for example, heat stress or the consequence of natural disasters, and indirectly through, for example, disrupted agriculture. Several of the health impacts of climate change identified by the IPCC (McCarthy, 2001) are relevant to Australia, including an increase in vector-, food- and water-borne infectious diseases; a decrease in winter deaths but an increase in heat-related deaths and illness; and an increased risk of drowning, diarrhoeal and respiratory diseases related to any increased flooding.

Australian studies are shedding new light on the likely impact of climate change on human health. The Federal Government has funded a formal assessment of the effects of climate change on health in Australia over the coming decades, entitled Human Health and Climate Change in Oceania: A Risk Assessment (McMichael et al., 2002). Each year, 1100 people aged over 65 die from temperature-related causes (summed in 10 major Australian cities). The projected rise in temperature for the next 50 years is predicted to result in a total of three to five thousand additional heat-related deaths a year (in the absence of adaptive measures, including the effect of population growth and aging, and with heat-related deaths defined as deaths estimated from the overall relationship between temperature and mortality rates from any cause that are in excess of the average for that time of year). Temperate cities show higher rates of deaths due to greater temperature extremes than tropical cities. The estimated increases in heat-related deaths were predicted to be far greater than the decreases in cold-related deaths. Canberra may experience positive effects from a reduced number of cold winter days in the short-term, but in the medium- to long-term these health gains are predicted to be outnumbered by additional heatrelated deaths. The Risk Assessment report also found that 1 in 10 year extreme rainfall events are expected to increase in almost all Australian states and territories by 2020, changing the number of floodrelated deaths and injuries to between an increase of 240% (in the southern areas of New South Wales near the Murray River) and a decrease of 35% (in north-eastern Tasmania).

Malaria is not endemic in Australia, with eradication achieved in the 1960s (only a handful of cases having been reported since then). The likelihood of malaria being reintroduced into Australia is very low – however model results in the health risk assessment report (McMichael et al., 2003) indicate that under climate change there is a hypothetical risk of the zone where Australia’s only malaria vector could exist, expanding as far south as Rockhampton, Gladstone and Bundaberg if adaptive measures are not taken. The tourism threat from an outbreak of vivax malaria in far north Queensland in 2002 and the recent high incidence of malaria among the Australian defence forces in East Timor underlines the priority that needs to be placed on prevention.

From 1991, when national reporting began, to 2002, 2595 cases of dengue had been recorded. The health risk assessment report (McMichael et al., 2003) estimated the region climatically suitable for dengue transmission, accounting for projected population change but not for the likely adaptive strategies that would reduce the risk of transmission. The model’s current risk region, including Broome, Darwin and Katherine in northern Australia and some coastline between Townsville and Mackay, is acknowledged as a slight underestimation. The model’s future risk regions were shown to increase in the simulations, as given in Table 4.2, although as noted above this does not account for adaptive measures.

Australian National University researchers have examined whether climate variables could be used to accurately predict epidemics of Ross River virus disease. Between 1991 and 2002 in Australia there were 51,761 notifications of the disease, which has no treatment (prevention remains the sole public health strategy). It is well recognised that weather directly affects the breeding, abundance, and survival of mosquitoes, the principal vector of many arboviruses. Using weather data from two regions in southeastern Australia, the scientists assessed Ross River virus disease data for the period 1991 to 1999. Two predictable epidemic patterns emerged, after either high summer rainfalls or high winter rainfalls. Lower than average spring rainfall in the pre-epidemic year turned out to be a prerequisite. The research findings are likely to be valuable to health authorities, as early warning of weather conditions conducive to Ross River virus disease outbreaks is possible with a high degree of accuracy in particular regions.

Researchers from Australian National University and Food Safety Australia have assessed the potential impact of climate change on food borne disease in the coming century. A link between climate and microbial food borne disease remains speculative. However, data show that Salmonella infections increase in summer, while Campylobacter infections increase in spring, similar to patterns seen overseas. In eastern Australia, rates of Salmonella notifications increase with decreasing latitude and consequently with increasing average yearly temperature. Food poisoning outbreaks may also be linked to unusually hot weather which can enhance bacterial replication. Reports of food poisoning outbreaks are higher during unusually hot summers in Australia. Assuming that a sustained temperature rise has a similar effect to monthly temperature variations, then the incidence of salmonellosis may rise in future decades, and, by extrapolation, the incidence of diseases caused by other food borne pathogens and toxins could also rise. Higher global temperatures could increase human exposure to toxins produced by cyanobacteria (blue-green algae) in water supplies and recreational water bodies, which can cause gastrointestinal and dermatological symptoms. Similarly, production of mycotoxins in agricultural produce could increase.