Objective: The world's climate will continue to change because of human influence. This is expected to affect health, mostly adversely. We need to compare the projected health effects in Australia arising from differing climate change scenarios to inform greenhouse gas emission (mitigation) policy.
Methods: We estimated health effects in Australia (heatwave mortality, dengue transmission regions) around 2100 under various greenhouse gas scenarios: "strong policy action" (efforts made now to reduce emissions) and "no policy action" (emissions continue at present high levels with no climate change-specific policies).
Results: Compared with no policy action, mitigation could reduce the number of deaths caused by hot temperatures among older Australians by 4,000-7,000 a year (range reflects likely population size at 2100). Under a scenario of "no action", the zone of potential transmission of dengue fever expands 1,800 kilometres (km) south, as far as Sydney. In contrast, by markedly constraining greenhouse gas emissions now, this southward extension could be limited to 600 km (to Rockhampton). The number of displaced people within the Asia-Pacific region could increase (by orders of magnitude) under the "no action" scenario because of adverse socioecological circumstances aggravated by climate change.
Conclusions: Additional health effects will accrue as a result of the projected climate change throughout this century, and individuals and health systems should be prepared for some level of adaptation. However, timely and strong policy action to reduce greenhouse gas emissions would diminish the extent and severity of estimated future health effects.