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Interest in public health aspects of climatic variability has grown greatly in the past decade. This has come about as knowledge about climatic changes and its impacts on society in general has increased, leading to greater efforts being made toward documenting and establishing possible links between climatic variability and changes in human health and well-being.

The idea that human health and disease are linked with the climate probably predates written history. The Greek physician Hippocrates (about 400 BC) related epidemics to seasonal weather changes. Robert Plot, Secretary to the Royal Society, took weather observations in 1683-84 and noted that if the same observations were made "in many foreign and remote parts at the same time" we would "probably in time thereby learn to be forewarned certainly of divers emergencies (such as heats, colds, dearths, plagues, and other epidemical distempers)." (Quoted in Symons 1900.) Public interest in the climate-health relationship strengthened during the 18th and 19th centuries after many studies indicated that certain diseases occurred more often in particular seasons. This close climate-health relationship is apparent in the titles of many books published during the 19th century, for instance, Climate and health in Australasia, by James Bonwick, published in London in 1886, and James Kilgour's 1855 book Effect of the climate of Australia upon the European Constitution in Health and Disease. These books were among many arguing whether Australia's climate was beneficial or harmful to human health (Nicholls 1997a).

The interest in climate as a precondition for disease probably reached its peak towards the end of the 19th century. For instance, Latham (1900) read a major review paper relating climate conditions to plague to the Royal Meteorological Society, in December 1899. Latham, who was President of the Society in 1890-92, noted that "while it is admitted that plague is due to a specific microbe, it cannot spread except under certain meteorological conditions associated with the conditions of the ground, which must be in such a state as to exhale what is necessary for the propagation and spread of this particular disease". The general acceptance that germs were the proximate cause of most diseases, and the increasing ability to treat diseases with pharmaceuticals, led to a decline in interest in the climate-health relationship until late in the 20th century. Major epidemics associated with the 1982/83 El Niño event, encouraged studies on the impact of climate on health, and concerns about possible impacts of climate change on health inspired further studies during the 1990s. Some of these studies (e.g., Nicholls 1986) seemed to confirm that Robert Pilot had been correct, in that climate observations (of the El Niño-Southern Oscillation) could be used to "forewarn" of some epidemics.

In this chapter, we document some key possible connections between aspects of climatic variability and variations in the incidence of some human diseases which appear to be modulated, at least partly, by climatic variations. Since the large-scale ocean-atmosphere phenomenon know as El Niño/Southern Oscillation (ENSO) represents the largest source of interannual variability in the modern climate system, ENSO will be a main focus of attention here. We also examine some aspects of climatic variability that lead to changes in human well-being, such as drought and floods, heat and cold waves, and other extreme events.

As this paper represents a contribution to the proceedings volume of the Second International Climate and History Conference, we try here to develop aspects of our subject matter related to their historical context. For a thorough treatment of the subject of climate change related to aspects of human health, we refer the reader to McMichael el al. (1996), and references therein, which is a state-of-the-art assessment prepared for several United Nations organizations. Other useful treatments of this subject may be found in Martens et al. (1999), Patz et al. (2000), and McMichael and Githeko (2001).