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

What Can Be Done to Control Seasonal Mortality During Global Warming?

It would be easy to look at these facts and say that we need do nothing. Global warming is not likely to increase overall mortality rates over time. People make their own adjustments to hotter summers, and in time this will prevent much increase in summer mortality rates.

Despite this, much needs to be done. Sudden heat waves can be expected to produce record high temperatures every few years as the climate warms. These will expose populations to higher environmental temperatures than they have ever encountered before. The record heat is accordingly liable to cause high mortality rates for a few days among people who are not prepared for it. This happened in France in the summer of 2003, with around 15,000 excess deaths in 2 weeks. Record temperatures can also cause unacceptable working conditions. One obvious solution is to install widespread air conditioning more widely in Europe, as in the United States. Unfortunately, this solution has penalties in the long term. The most important is high energy consumption, which accelerates global warming, as it requires increased generation of electricity and this in turn involves burning more fossil fuel.

Alternative strategies for keeping cool in hot weather involve the design and management of buildings. One important element in this is high thermal insulation in their outer walls and high thermal mass internally, to provide a more even indoor temperature throughout the 24-hour cycle. It is particularly important to prevent sunlight coming in through windows, causing greenhouse heating. External slatted shutters are a traditional and effective way of doing this in southern Europe. Windows can be opened at night, and then closed after dawn for as long as the interior of a building remains cooler than the outside air. Cooking should be kept to a minimum in places where it can warm up living space and increase humidity. Crowding of people indoors will also increase temperature and humidity. Once the interior of a building does become uncomfortably hot, a combination of light clothing, air movement from a fan, open windows, and a sprinkling of water on the clothing can normally control heat stress. People should continue to eat regular meals with moderate salt content and to drink water in hot weather, even if they do not feel hungry or thirsty.

These measures will normally be effective even for people who are elderly or vulnerable because of illnesses such as diabetes, or who are taking drugs that suppress sweating. Sprinkling water on clothing can substitute for sweating and allow evaporative cooling even in these people. Evaporative cooling requires that the air should not be saturated; when heat stress develops, ventilation by air from an open window will provide the unsaturated moving air needed for evaporative cooling. Outside air is not saturated at hot times of the day during heat waves in temperate regions.

Anyone who becomes seriously overheated, with a mouth temperature around or above 104.9°F, needs to be cooled immediately. This should be started at once rather than waiting for help from the emergency services. If other measures are difficult to implement, immersion in a cool bath can used, but it must be remembered that very cold water will cause vasoconstriction. This can retard cooling, so that cool rather than cold water should be used. Immediate measures of that kind are far more effective than transporting a patient to hospital. A high proportion of those who died in France in the heat wave of 2003 appear to have done so in hospitals. The objective should be to keep people cool at home, and to cool them there. However, hospitals and other institutions containing numbers of elderly and other vulnerable people have a particular need for air conditioning, unless the design of the building can keep those within at safe temperatures with any level of outdoor temperature that can reasonably be expected. Finally, measures to control and treat tropical diseases need to be available if these diseases spread outside their present ranges.

Some of these measures require long-term planning, but warnings with advice on preventing and treating heat stress are important when heat waves are forecast. Broadcasting advice together with such forecasts can also allow elderly people and their neighbors to check, for example, that fans and water are available and that windows can be opened. Air conditioning will be increasingly needed in heat waves, but a possible strategy is to have it available in most regions but to use it only as a second line of defense when other methods fail or become excessively burdensome.

Important as such measures against heat stress are, we should not lose sight of the fact that even in climates as warm as southern Europe or North Carolina, cold weather causes more deaths than hot weather. The importance of warm housing in preventing winter death is well recognized,[30] but the large contribution made by outdoor cold stress to winter death[1,31] is generally not. Global warming will reduce this at first, but the improvement is not likely to continue without action to promote defenses against cold. People in regions with mild winters become careless about cold stress, protect themselves less effectively against cold, and generally have more winter deaths than people in colder regions.[1,24,25] Climatic warming therefore calls for action to control cold stress as well as heat stress. If this is taken, rising temperatures could reduce overall mortality rates.


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