Socioeconomic scenarios can be constructed in the same variety of ways and for the same variety of purposes as global change scenarios in general. In practice, a variety of approaches may be combined in a single exercise. The UNEP country studies program has developed detailed guidance on construction and use of socioeconomic scenarios (Tol, 1998). This guidance emphasizes the importance of avoiding simple extrapolation-especially for developing countries, which may be undergoing demographic or economic transition; the role of formal modeling in filling in, but not defining, scenarios; and the role of expert judgment in blending disparate elements into coherent and plausible scenarios.
Most socioeconomic scenarios cover several different topics or domains, such as population or economic activity. Table 3-1 shows the range of issues covered in recent scenario or scenario-based exercises.
Population and economic activity are characterized in quantitative terms in most scenario exercises. The degree of disaggregation according to world region, country, or sector varies from one study to another. Coverage of other socioeconomic domains also can vary markedly among different activities.
Some scenarios incorporate explicit assumptions about underlying socioeconomic drivers of change such as social values and governance institutions. These scenarios usually are generated through synthetic or expert judgment-led approaches, expressed in qualitative terms. Social values can affect the willingness of societies to preserve ecosystems or protect biodiversity. Institutional and governance factors affect the capacity of a society to organize and direct the resources needed to reduce climate vulnerability (Adger, 1999). Qualitative factors such as institutional effectiveness and social values are key determinants of the effectiveness of coping strategies for adapting to climate change (see Chapter 18). They determine adaptive capacity and hence the vulnerability of socioeconomic systems. They are critical in any assessment of the implications of climate change for development, equity, and sustainability (Munasinghe, 2000).
Technology critically affects the capacity to adapt to climate change; it confers opportunities and risks. For example, genetic modification of crops and other developments in agricultural technology could enhance that sector's ability to adapt to different climatic conditions. However, excessive reliance on one particular strain of plant might increase vulnerability.
Technological change must be characterized in quantitative and qualitative terms. It may be very difficult to identify specific features of a technology that could affect vulnerability to climate change. Expert judgments are needed about the direction in which change takes place, public acceptability of different options, and the rate of adoption in the marketplace. Quantitative assumptions will be needed about the rate of improvement of a technology, including its cost, overall efficiency in using resources to meet the need for a given service, and possible impacts at various scales.
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