The potential health impacts of climate variability and change are wide-ranging, from direct local impacts, through indirect effects occurring at the regional or ecosystem level, to long-term effects on the sustainability of global systems. In order to understand these potential impacts, there is a need to broaden the scope of health impact assessment beyond the traditional emphasis on local effects. Using a historical ‘analogue’ approach, I investigated some health impacts of climate variations on progressively increasing scales.
Firstly, I examined the relationship between the daily number of deaths, weather and ambient particulate air pollution in the city of Christchurch, New Zealand, using Poisson regression models and controlling for season using a parametric method. I concluded that high temperatures and particulate air pollution are independently associated with increased daily mortality in Christchurch. The fact that these results are consistent with those of similar studies in other countries strengthens the argument that the associations are likely to be causal.
I conducted an ecological study linking the prevalence of adult asthma symptoms with climate in the 93 New Zealand general electorates. For each electorate, the 12-month period prevalence of self-reported asthma symptoms was determined using a random sample of adults on the electoral roll. Long-term average climate was estimated using a national climate database and a geographic information system. I concluded that on short (day-to-day) time scales, low temperatures may have a direct effect on asthma symptoms, but that warmer average temperatures are associated with increased asthma prevalence. The reasons for this are unclear, although it is possible that on longer term (annual) time scales, higher temperatures are associated with higher levels of allergen exposure.
Dengue and Ross River virus are transmitted by mosquitoes, and the spread of these pathogens may therefore be influenced by climate. On a regional, interannual scale, I examined the predictability of outbreaks of dengue (in the islands of the South Pacific) and Ross River virus (in Australia) in relation to climate. I found that, in certain regions, climate changes associated with El Niño Southern Oscillation may trigger epidemics of arboviral disease.
Ciguatera (fish poisoning) is the most frequent cause of human illness caused by ingestion of marine toxins. I calculated correlations between reports of fish poisoning in individual Pacific Islands, estimates of local sea surface temperature and the Southern Oscillation Index. I found positive correlations between the annual incidence of fish poisoning and local warming of the sea surface in a group of islands that experience warming during El Niño conditions. I speculate that ciguatera may be a sensitive indicator of environmental stress in coral reef systems.
In the final chapter, I discuss how these results might be applied to the assessment of potential future impacts of long-term climate change at the global scale. I conclude that the major public health impacts of climate change are likely to occur via indirect mechanisms and will be strongly modulated by population vulnerability. These impacts are only partly amenable to traditional public health interventions. I argue that ecologically sustainable development will be an essential prerequisite for effective adaptation to climate change. In addition to reducing adverse health impacts of climate change in the long-term, ecologically sustainable development would lead to two other major benefits: improvement in human health status in the short-term and a reduction in the major driving forces of climate change. At the global level, interactions and feedbacks between systems are critical determinants of long-term outcomes. From an eco-epidemiological perspective, the study of climate change becomes inseparable from the study of global change more generally.