Proc. Natl Acad. Sci. USA http://doi.org/hqz (2012)

Credit: © ISTOCKPHOTO/THINKSTOCK

Climatic changes can influence human health and survival either through direct effects, such as extreme heat or floods, or through indirect means, such as changes in crop yield, infectious disease outbreaks, conflict or displacement and its consequences.

Anthony McMichael, of the National Centre for Epidemiology and Population Health at the Australian National University, investigated historical climate events and their effect on human populations over the past several thousand years. He concludes that the speed and strength at which a climatic change occurs significantly affects the outcome. Long-term climate change has contributed to the decline in civilizations, through food shortages, famine and associated unrest. Medium-term climate change has lead to political upheaval as a result of hunger, infectious diseases and poverty. However, societies have generally been able to adapt to short-term climate cycles, such as El-Niño, except for extreme cases. Historically, the greatest climate threat has been drought, famine and starvation.

These historic impact patterns suggest that current human-caused climate change — which could be extreme and more rapidly evolving than previous events — can be expected to affect all human populations to some degree.