Introduction

Excess carbon dioxide, methane, and other gases which trap heat are accumulating in the troposphere, the earth's lower atmosphere, because of the scale and type of human economic activity. Climate scientists predict that the resultant increase in the troposphere's “radiative forcing” will warm the earth's surface.1 2 3 Indeed, in its recent second assessment report, the Intergovernmental Panel on Climate Change—a multidisciplinary scientific body established by the United Nations in 1988 to advise governments—concluded that on balance an anthropogenic influence upon the global climate was now “discernible.” 1

The intergovernmental panel forecasts an increase in the average world temperature of 1.0-3.5°C over the coming century.1 This forecast is necessarily uncertain because the sensitivity of climate to atmospheric change is imperfectly understood and because future trends in gaseous emissions and modulating processes (for example, the cooling effects of industrial aerosol emissions) cannot be foreseen accurately. Nevertheless, the expected rate of climate change over the coming century would be far greater than any natural change in world climate since the advent of agriculture 10 000 years ago.

Anthropogenic climate change signifies that for the first time the aggregate global impact of humankind exceeds the physical and ecological limits of the biosphere.4 The potential consequences of this and other global changes (including stratospheric ozone depletion, loss of biodiversity, worldwide land degradation, and depletion of aquifers) are wide ranging. We can expect that climate change will affect the health and wellbeing of human populations in diverse ways. This greatly extends the temporo-spatial scale of environmental health beyond our usual concern with localised and immediate exposures to toxic or infectious agents.4 A major research task, therefore, is the application of current knowledge to forecasting probable health effects. The primary objective is to provide indicative forecasts of an important consequence that will …