11.4.11 Human health
One of the most significant health impacts of climate change is likely to be an increase in heat-related deaths. Assuming no planned adaptation, the number of deaths is likely to rise from 1,115/yr at present in Adelaide, Melbourne, Perth, Sydney and Brisbane to 2,300 to 2,500/yr by 2020, and 4,300 to 6,300/yr by 2050, for all SRES scenarios, including demographic change (McMichael et al., 2003). In Auckland and Christchurch, a total of 14 heat-related deaths occur per year in people aged over 65, but this is likely to rise to 28, 51 and 88 deaths for warmings of 1, 2 and 3°C, respectively (McMichael et al., 2003). Demographic change is likely to amplify these figures. By 2100, the Australian annual death rate in people aged over 65 is estimated to increase from a 1999 baseline of 82 per 100,000 to 131-246 per 100,000, for the SRES B2 and A2 scenarios and the 450 ppm stabilisation scenario (Woodruff et al., 2005). Australian temperate cities are likely to experience higher heat-related deaths than tropical cities, and the winter peak in deaths is likely to be overtaken by heat-related deaths in nearly all cities by 2050 (McMichael et al., 2003). In New Zealand, the winter peak in deaths is likely to decline.
There are likely to be alterations in the geographical range and seasonality of some mosquito-borne infectious diseases. Fewer but heavier rainfall events are likely to affect mosquito breeding and increase the variability in annual rates of Ross River disease, particularly in temperate and semi-arid areas (Woodruff et al., 2002, 2006). The risk of establishment of dengue fever is likely to increase through changes in climate and population sensitivity in both tropical and temperate latitudes (Sutherst, 2004). Dengue is a substantial threat in Australia: the climate of the far north already supports Aedes aegypti (the major mosquito vector of the dengue virus); and outbreaks of dengue have occurred with increasing frequency and magnitude in far-northern Australia over the past decade. Projected climate changes in north-eastern Australia, combined with population growth, are likely to increase the average annual number of people living in areas suitable for supporting the dengue vector (an additional 0.1 to 0.3 million exposed in 2020, and 0.6 to 1.4 million in 2050) (McMichael et al., 2003). Malaria is unlikely to become established unless there is a dramatic deterioration in the public health response (McMichael et al., 2003). In New Zealand, parts of the North Island are likely to become suitable for breeding of the major dengue vector, while much of the country becomes receptive to other less-efficient vector species (De Wet et al., 2001; Woodward et al., 2001). The risk of dengue in New Zealand is likely to remain below the threshold for local transmission beyond 2050 (McMichael et al., 2003).
Warmer temperatures and increased rainfall variability are likely to increase the intensity and frequency of food-borne (D’Souza et al., 2004) and water-borne (Hall et al., 2002) diseases in both countries. Indigenous people living in remote communities are likely to be at increased risk due to their particular living conditions and poor access to services. The annual number of diarrhoeal hospital admissions among Aboriginal children living in central Australia is likely to increase 10% by 2050, assuming no change in current health standards (McMichael et al., 2003). The relationship between drought, suicide and severe mental health impacts in rural communities (Nicholls et al., 2006) suggests that parts of Australia are likely to experience increased mental health risks in future. Impacts on aeroallergens and photochemical smog in cities remain uncertain. High concentrations of bushfire smoke play a role in increasing hospital presentations of asthma (Johnston et al., 2002), so projected increases in fire risk may lead to more asthma.