Conceptual and methodological challenges in predicting the health impacts of climate change.

Describing (not to mention quantifying) the anticipated adverse health impacts of global climate change poses basic challenges to biomedical science. First and foremost, it is beset with uncertainties and complexities; it is necessarily an 'If-Then' exercise, that takes as given climatologists' estimates of the plausible range of greenhouse-induced climate change over the coming century. The health impacts of climate change would generally not occur via the familiar direct-acting mechanisms that characterise local environmentally-induced toxicology or pathophysiology; therefore they would lack the mechanistic directness-of-effect that epidemiological research methods are best equipped to study. Rather, the health impacts would occur on a larger scale, and would result predominantly from perturbations of natural biogeochemical systems that reduce Earth's capacity for life support. Therefore, scientists will need to address the assessment of impacts within an ecological framework, and with an unusually long time horizon. This assessment requires a new capacity for systems-based thinking, predictive modelling, and dealing with uncertainty. Scientists, policy-makers and general public will have to adjust to unfamiliar styles of 'anticipatory' science, with an unusual overlay of uncertainty and provisionality.