At the global scale, there is considerable variation among countries with regard to their capacity to adapt to climate change. Given their economic affluence and stability; their institutions and infrastructures; and their access to capital, information, and technology, developed nations are broadly considered to have greater capacity to adapt than developing regions or countries in economic transition (Goklany, 1995; Burton, 1996; Magalhães, 1996; Toman and Bierbaum, 1996). In general, countries with well-developed social institutions supported by higher levels of capital and stores of human knowledge are considered to have greater adaptive capacity (Smith and Lenhart, 1996). Adaptation options—including traditional coping strategies—often are available in developing countries and countries in transition; in practice, however, those countries' capacity to effect timely response actions may be beyond their infrastructure and economic means (IPCC, 1997). For those countries, the main barriers are (Smith, 1996; IPCC, 1998; Mizina et al., 1999):

• Financial/market (uncertain pricing, availability of capital, lack of credit)
• Institutional/legal (weak institutional structure, institutional instability)
• Social/cultural (rigidity in land-use practices, social conflicts)
• Technological (existence, access)
• Informational/educational (lack of information, trained personnel).

A study by Rosenzweig and Parry (1994) found considerable disparity between developed and developing countries in terms of potential adverse effects of climate change on agricultural systems; developing countries suffer the greatest losses. In addition, poorer, developing regions presumably will face stricter constraints on technology and institutions (Fankhauser and Tol, 1997) and that measures taken in response to climate change may be very demanding financially (Dvorak et al., 1997; Deschingkar, 1998). Researchers also believe that compared to industrialized countries, developing countries possess a lower adaptive capacity as a result of greater reliance on climatic resources (Schelling, 1992; Fankhauser and Tol, 1997).

There is some suggestion, however, that the complex, multi-species, low- to middle-intensity farming systems that characterize agricultural endeavors in the developing world may have greater adaptive capacity under conditions of global climate change than western monocultures (Ramakrishnan, 1998). An example is found in the village of Maatisar (India), where local institutions in the past have operated on the principle of "moral economy," or guaranteed subsistence to all households in the village. These institutions have eroded over time, however, giving way to competitive market relations that do not guarantee subsistence during times of drought. As a result, the capacity of individual households to withstand seasonal fluctuations has decreased over time (Chen, 1991). Magalhães (1996) describes how northeast Brazil has become more vulnerable to droughts as inappropriate land use overstresses natural land and water resources and as the capacity to cope is limited by poverty.

Acceptance of western economic ideals coupled with increasing and rapid development may reduce the capacity of traditional societies to adapt (Watts, 1983; Chan and Parker, 1996). In the case of traditional or indigenous societies, the pursuit of western/ European-style development trajectories may modify the nature of adaptive capacity (some improved, some diminished) by introducing greater technology dependence and higher density settlement and by devaluing traditional ecological knowledge and cultural values (Newton, 1995). For example, notwithstanding remarkable adaptations to a harsh climate, the North American Inuit continue to be vulnerable to climate change as a result of their dependence on wildlife (which are climate-sensitive). This vulnerability has been reduced by technological enhancement of adaptive capacity through the acquisition of snowmobiles, motorized boats, and even sonar. Such technological advances have allowed Inuit communities to become far more "fixed" than before. Many of the most densely populated areas lie at least partially within a few meters of sea level. This lack of "semi-permanence" may actually increase the Inuits' vulnerability to potential climate-induced sea-level rise by decreasing their capacity to adapt through retreat or migration (Rayner and Malone, 1998).

Although there is considerable literature on the determinants of adaptive capacity and examples of how they influence the adaptability of particular communities, there is little scholarship (and even less agreement) on criteria or variables by which adaptive capacity can be measured and by which the adaptive capacity of global regions can be quantitatively compared. Various studies have attempted to identify overall trends that cause increased or decreased vulnerability to environmental hazards (Torry, 1979; Lamb, 1982; Warrick and Reibsame, 1983; Ausubel, 1991b; Blaikie et al., 1994); unfortunately, however, the concept of vulnerability "does not rest well on a developed theory, nor is it associated with widely accepted indicators or methods of measurement" (Bohle et al., 1994).

Even less progress has been made in measuring adaptive capacity. In the context of African agriculture, Downing et al. (1997) attempt to quantitatively measure relative adaptive capacity of regions by using crude surrogates such as gross national product (GNP). Empirical local-level studies of vulnerability are so complex, however, that attempts to describe patterns or estimate trends at global or regional scales are extremely difficult (Liverman, 1990; Downing, 1991; Dow, 1992). These "difficulties in generalizing about levels of vulnerability even in a relatively small community" are demonstrated by Adger and Kelly's (1999) study of vulnerability to climate change in Vietnam. Because vulnerability is a composite concept, social change has the potential to make individuals or activities more vulnerable in some ways and less vulnerable in others (Rayner and Malone, 1998). The influence of changes in the determinants of adaptive capacity are not necessarily direct or clear, rendering the attempt to develop systematic indices for measurement and comparison a difficult task.

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