The threat to human health is of a more fundamental kind than is the threat to the world's economic system, says Professor McMichael, a Professor of public health from the Australian National University. "Climate change is beginning to damage our natural life-support system," he says.
The risks to health are many, and include the impact of heat waves, floods and wildfires, changes in infectious disease patterns, the effect of worsening food yields and loss of livelihoods.
The World Health Organisation estimates that a quarter of the world's disease burden is due to the contamination of air, water, soil and food - particularly from respiratory infections and diarrhoeal disease.
Climate change, says Professor McMichael, will make these and other diseases worse. While it is unlikely to cause entirely new diseases it will alter the incidence, range and seasonality of many existing health disorders. So, for example, by 2080 between 20 and 70 million more people could be living in malarial regions due to climate change.
The adverse health impacts will be much greater in low-income countries and vulnerable sub-populations than in richer nations.
Professor McMichael says:
"Poverty cannot be eliminated while environmental degradation exacerbates malnutrition, disease and injury. Food supplies need continuing soil fertility, climatic stability, freshwater supplies and ecological support (such as pollination). Infectious diseases cannot be stabilised in circumstances of climatic instability, refugee flows and impoverishment."
The relationship between the environment and health is complex. For example, as India modernises it expects the health of its population to improve, yet industrialisation also means a rapidly increased level of coal-burning and greater global emissions. This in turn leads to climate change, the impact of which is felt most by vulnerable populations.
Professor McMichael concludes that the global changes we are seeing now are unprecedented in their scale, and healthcare systems should develop strategies to deal with the resulting growing burden of disease and injury. More bold and far-sighted policy decisions need to be taken at national and international level to arrest the process and health professionals "have both the opportunity and responsibility to contribute to resolving this momentous issue."