Adaptation measures can be used effectively to greatly reduce many of the potential health impacts of climate change (Gubler, 1998d; McMichael and Kovats, 2000; WHO, 2000). The most important, cost-effective, and urgently needed measure is to rebuild public health infrastructure. In very many countries of the world, this infrastructure has declined in recent years. Many diseases and public health problems that otherwise may be exacerbated by climate change could be prevented substantially or completely with adequate financial and public health resources. These resources would encompass public health training programs, research to develop and implement more effective surveillance and emergency response systems, and sustainable prevention and control programs.

Understanding vulnerability to changes in ranges or rates of diseases is the first step in addressing adaptive capacity. Adaptation involves the ability to change behavior or health infrastructure to reduce these potential negative impacts or increase potential positive impacts of climate change. Interventions early in the causal chain of disease are preferred (e.g., "primary" prevention to remove or reduce risks before any human cases occur). To the extent that this is not always feasible (or the risk factors unknown), "secondary prevention" or surveillance for early warning to prevent any further cases also is important.

Adaptation is a function of several societal systems, including access to financial resources (for individuals and populations), technical knowledge, public health infrastructure, and the capacity of the health care system. Note that there is much similarity in the determinants of adaptive capacity and those of vulnerability (see Section 9.3). Adaptation can occur via two routes: autonomous adaptation, which is the natural or spontaneous response to climate change by affected individuals, and purposeful adaptation, which is composed of planned responses to projected climate change—typically by governmental or other institutional organizations (MacIver and Klein, 1999). Purposeful adaptation also can occur via deliberate modification of personal, family, and community lifestyles, particularly in response to public education programs. Anticipatory adaptations are planned responses that take place in advance of climate change.

Adaptation to the impacts of climate change may occur at the population, community, or personal level (see Table 9-4). The capacity to adapt to potential changes in the climate will depend on many factors, including improving the current level of public health infrastructure; ensuring active surveillance for important diseases; and continuing research to further our understanding of associations between weather, extreme events, and vector-borne diseases. In addition, continuing research into medical advances required for disease prevention, control, and treatment—such as vaccines, methods to deal with drug-resistant strains of infectious agent, and mosquito control—is needed. More generally, research is needed to identify adaptation needs, evaluate adaptation measures, assess their environmental and health implications, and set priorities for adaptation strategies. The following subsections outline adaptive measures that have been developed for two areas of climate change impacts on health.

Major impacts on human health may occur via changes in the magnitude and frequency of extreme events (see Table 3-10 and TAR WGI Chapter 9). Following Hurricanes George and Mitch, a range of policies to reduce the impacts of such extreme events has been identified (PAHO, 1999):

• Undertaking vulnerability studies of existing water supply and sanitation systems and ensuring that new systems are built to reduce vulnerability
• Developing improved training programs and information systems for national programs and international cooperation on emergency management
  
• Developing and testing early warning systems that should be coordinated by a single national agency and involve vulnerable communities providing and evaluating mental health care, particularly for those who may be particularly vulnerable to the adverse psychosocial effects of disasters (e.g., children, the elderly, and the bereaved).

Adaptation strategies to reduce heat-related mortality in vulnerable cities around the world include weather-based early warning systems (WMO, 1997; Ortiz et al., 1998). A different system must be developed for each city, based on that city's specific meteorology. Specific weather/health thresholds are determined and used to call health warnings or advisories. Many systems are based on synoptic methodology; specific "offensive" air masses are identified and forecasts are developed to determine if they will intrude into a city within the next 60 hours. Two systems are under construction for Rome, Italy, and Shanghai (WMO, 1997).

Institutional and cultural barriers to the use of seasonal forecast information remain. Decisionmakers should be educated or encouraged to use scientific information that may lead to reduction in losses from natural disasters (Pfaff et al., 1999).

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