The Impact of Global Warming on Health and Mortality

W. R. Keatinge, MA, MB, BCHIR, PHD, FRCP; G. C. Donaldson, BA, PHD


South Med J. 2004;97(11) 

In This Article

Abstract and Introduction

Initial concern about the possible effects of global warming on infections has declined with the realization that the spread of tropical diseases is likely to be limited and controllable. However, the direct effects of heat already cause substantial numbers of deaths among vulnerable people in the summer. Action to prevent these deaths from rising is the most obvious medical challenge presented by a global rise in temperature. Strategies to prevent such deaths are in place to some extent, and they differ between the United States and Europe. Air conditioning has reduced them in the United States, and older technologies such as fans, shade, and buildings designed to keep cool on hot days have generally done so in Europe. Since the energy requirements of air conditioning accelerate global warming, a combination of the older methods, backed up by use of air conditioning when necessary, can provide the ideal solution. Despite the availability of these technologies, occasional record high temperatures still cause sharp rises in heat-related deaths as the climate warms. The most important single piece of advice at the time a heat wave strikes is that people having dangerous heat stress need immediate cooling, eg, by a cool bath. Such action at home can be more effective than transporting the patient to hospital. Meanwhile, it must not be forgotten that cold weather in winter causes many more deaths than heat in summer, even in most subtropical regions, and measures to control cold-related deaths need to continue.

Infections in the summer months were largely brought under control by the beginning of the last century. Since then, winter cold has been the major seasonal factor causing death in all but tropical regions of the world. However, more direct effects of heat in summer cause a smaller but significant number of deaths. These sometimes increase sharply during record high temperatures in particular regions, and recent concerns about the effects of global warming on health have concentrated on the need to prevent these deaths from increasing. Both the cold-related and the heat-related deaths occur almost entirely in elderly people. Both are largely avoidable, and both need to be taken into account when considering the effects of rising temperatures.

Global warming has now been under way for long enough to allow some direct assessments to be made of its effects on seasonal deaths. These effects are often very different from earlier expectations, and depend a great deal on the effectiveness of measures taken to limit heat stress on people. These measures in turn vary greatly between Europe and North America. The purpose of this article is to summarize current information on the ways in which hot and cold weather cause deaths and on measures to prevent these.

Mortality rates are generally lowest at a mean daily temperature around 66°F,[1,2,3,4,5] the precise level varying with region. The mortality rate in each region rises as temperature either falls or rises from that level. The numbers of these excess deaths per year give the best measures of both heat-related and cold-related mortality rates. An older measure that had been used for winter mortality rate alone was the number of deaths per million during December to March, as an excess over mean mortality rate during the rest of the year. That is simple to calculate and can often provide a rough comparison of winter deaths at different times and in different regions, but it has major drawbacks. The worst of these is that it is determined by death caused by hot weather in summer as well as cold weather in winter. If there are more deaths caused by hot weather than cold weather, that comparison will suggest no excess winter deaths in that region, although cold is in fact producing high mortality rates in winter, balanced by high mortality rates caused by heat in summer.


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