Background climate and annual weather patterns are key factors in agricultural productivity, despite technological advances such as improved crop varieties and irrigation systems. As temperature, rainfall, and soil moisture change, plant physiology is affected; so too is the much less predictable risk of a change in patterns of plant pests and pathogens. There are many social, economic, and environmental influences on agricultural, horticultural, and livestock productivity. Climate change represents an additional pressure on the world food supply system. That system, which has yielded an overall increase in per capita food supplies over the past 4 decades, has shown signs of faltering over the past decade. There is ongoing scientific debate about the relative importance of economic, technical, and ecological influences on current food yields (Waterlow et al., 1998; Dyson, 1999). Optimists point to falling food prices; pessimists point to falling soil fertility.

Modeling studies (reviewed in Chapter 5) indicate that, under climate change, yields of cereal grains (the world's dominant food commodity) would increase at high and mid-latitudes but decrease at lower latitudes. Furthermore, this disparity would become more pronounced as time progresses. The world's food system may be able to accommodate such regional variations at the global level, with production levels, prices, and the risk of hunger relatively unaffected by the additional stress of climate change. To minimize possible adverse consequences, a dual development program is desirable. Adaptation should be undertaken via continued development of crop breeding and management programs for heat and drought conditions. These will be immediately useful in improving productivity in marginal environments today. Mitigation strategies should be implemented to try to reduce further enhanced global warming. However, recent work suggests that the main benefits of mitigation will not accrue until late in the 21st century (Parry et al., 1998).

The United Nations Food and Agriculture Organization (FAO) estimates that in the late 1990s, 790 million people in developing countries did not have enough to eat (FAO, 1999). The FAO report on food insecurity has identified population groups, countries, and regions that are vulnerable. For example, nearly half the population in countries of central, southern, and east Africa are undernourished. Environmental factors, including natural factors and those that are a consequence of human activities, can limit agricultural potential. These factors include extremely dry or cold climates, poor soil, erratic rainfall, steep slopes, and severe land degradation. The FAO report further states that undernutrition and malnutrition prevail in regions where environmental, economic, and other factors expose populations to a high risk of impoverishment and food insecurity.

Undernutrition is a fundamental cause of stunted physical and intellectual development in children, low productivity in adults, and susceptibility to infectious disease in everyone. Decreases in food production and increases in food prices associated with climate change would increase the number of undernourished people. Conversely, if food production increases and food prices decrease, the number of undernourished people would fall, but populations in isolated areas with poor access to markets still may be vulnerable to locally important decreases or disruptions in food supply.

Table 9-4: Options for adaptation to reduce health impacts of climate change.
Health Outcome	Legislative	Technical	Educational- Advisory	Cultural and Behavioral
Thermal stress	Building guidelines	Housing, public buildings, urban planning to reduce heat island effects, air conditioning	Early warning systems	Clothing, siesta
Extreme weather events	Planning laws Building guidelines Forced migration Economic incentives for building	Urban planning Storm shelters	Early warning systems	Use of storm shelters
Air quality	Emission controls Traffic restrictions	Improved public transport, catalytic converters, smokestacks	Pollution warning	Carpooling
Vector-borne diseases		Vector control Vaccination, impregnated bednets Sustainable surveillance, prevention and control programs	Health education	Water storage practices
Water-borne diseases	Watershed protection laws Water quality regulation	Genetic/molecular screening of pathogens Improved water treatment (e.g., filters) Improved sanitation (e.g., latrines)	Boil water alerts	Washing hands and other hygiene behavior Use of pit latrines

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