CLIMATE EFFECTS ON HUMAN HEALTH

CLIMATE EFFECTS ON HUMAN HEALTH

Prepared by:

Laurence S. Kalkstein
Kathleen M. Valimont

A. FINDINGS

1. Weather has a profound effect on human health and well-being. It has been demonstrated that weather is associated with changes in birth rates, and sperm counts, with outbreaks of pneumonia, influenza and bronchitis, and is related to other morbi dity effects linked to pollen concentrations and high pollution levels.

2. Large increases in mortality have occurred during previous heat and cold waves. It is estimated that 1,327 fatalities occurred in the United States as a result of the 1980 heat wave; the number occurring in Missouri alone accounted for over 25% of the total.

3. Hot weather extremes appear to have a more substantial impact on mortality than cold wave episodes. Most research indicates that mortality during extreme heat events varies with age, sex, and race. Factors associated with increased risk from hea t exposure include alcoholism, living on higher floors of buildings, and the use of tranquilizers. Factors associated with decreased risk are use of air conditioning, frequent exercising, consumption of fluids, and living in shaded residences. Acclimatiza tion may moderate the impact of successive heat waves over the short term.

4. Threshold temperatures for cities, which represent maximum and minimum temperatures associated with increases in total mortality, have been determined. These threshold temperatures vary regionally; for example, the threshold temperature for wint er mortality in mild southern cities such as Atlanta is 0deg.C and for more northerly cities, such as Philadelphia, it is -5deg.C.

5. Humidity has an important impact on mortality since it contributes to the body's ability to cool itself by evaporation of perspiration. It also has an important influence on morbidity in the winter because cold, dry air leads to excessive dehydr ation of nasal passages and the upper respiratory tract and increased chance of microbial and viral infection.

6. Precipitation in the form of rainfall and snow is also associated with changes in mortality. In New York City, upward trends in mortality were noted the day after snowfalls that had accumulated 2 inches or more. In Detroit where snow is more com mon, the snowfall accumulation exceeded 6 inches before mortality increases were noted.

7. If future global warming induced by increased concentrations of trace gases does occur, it has the potential to significantly affect human mortality. In one study, total summertime mortality in New York City is estimated to increase by over 3,20 0 deaths per year for a 7deg.F trace-gas-induced warming without acclimatization. If New Yorkers fully acclimatize, the number of additional deaths are estimated to be no different than today. It is hypothesized that, if climate warming occurs, some addit ional deaths are likely to occur because economic conditions and the basic infrastructure of the city will prohibit full acclimatization even if behavior changes.

8. Two areas of important future research include investigation of morbidity impacts and the costs to society of indirect impacts (e.g., costs associated with modifying living and working areas, decreases productivity, and other climate/stress-indu ced impacts).

B. INTRODUCTION

There is a large body of literature devoted to the impact of variable climate on human well-being. Most of the research has been done by medical scientists, and a minor amount of the work has been performed by climatologists. This section will attempt to describe much of the relevant research that has been published to date. Topics will be subdivided on the basis of weather events, as many of the manuscripts evaluated employ a regression technique to determine the impacts of one or more climatic events on human health.

There appears to be general agreement that weather has a profound impact on human health, but scientists do not agree on the precise mechanisms involved. For example, some of the research suggests that extreme weather events appear to have the greatest in fluence on health. Driscoll (1971a) correlated daily mortality for 10 cities with weather conditions in January, April, July, and October and found that large diurnal variations in temperature, dewpoint, and pressure were associated with many high mortali ty days. In addition, hot, humid weather with concomitant high pollutant concentrations were also contributory mechanisms. Other studies do not attribute large variations in mortality to extreme events, but rather to the normal seasonal changes in weather (Persinger, 1980).

The importance of determining the role of weather in human health cannot be understated. Reports of large increases in mortality during heat and cold waves are commonplace; for example, the National Oceanic and Atmospheric Administration (NOAA) estimated that 1,327 fatalities in the United States were directly attributed to the 1980 heat wave; fatalities in Missouri alone accounted for over 25% of the total excess deaths (U.S. Department of Commerce, 1980). During a heat wave in 1963, more than 4,600 deat hs above a computed mean occurred in June and July in the eastern United States (Schuman et al., 1964). The impact of weather on human well-being goes beyond mortality; even birth rates and sperm counts appear to be affected by meteorological phenomena (C alot and Blayo, 1982; Tjoa et al., 1982; White, 1985).

This report will concentrate on the effects of weather upon human mortality. However, there are numerous other impacts of weather on the general health of the population, including morbidity, short-term changes in mood, emotional well-being, and aberratio ns from normal behavior. For example, asthma attacks, many of which occur from inhalation of airborne agents such as spores and molds, appear to be related to various meteorological variables (White, 1985). Goldstein (1980) found that clusters of attacks are preceded by the passage of a cold front followed by a high pressure system. Morbidity attributed to pneumonia, influenza, bronchitis, and probably many other illnesses is also weather-related (White, 1985).

In addition, several atmospheric phenomena that are indirectly related to weather and might have an impact on mortality (the most notable being atmospheric pollutants and pollen concentrations) are not included in this review. A partial annotated bibliogr aphy of pollen concentration is presently available (Kalkstein and Robeson, 1984), but there is little research comparing weather/pollen relationships to human health. Meteorologic conditions exert a large influence on pollution concentrations and dispers ion and they also affect the impact of pollution on mortality and morbidity. Much of the literature on this topic has already been summarized (Stern, 1977).

Probably the most intensively-studied weather element that affects human mortality is air temperature, especially the impact of summer heat. A detailed description of temperature/mortality relationships follows.

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