Susceptibility to climate change differs across sectors and regions. A clear example is sea-level rise, which mostly affects coastal zones (see Box 19-2). People living in the coastal zone generally will be negatively affected by sea-level rise, but the numbers of people differ by region. For example, Nicholls et al. (1999) found that under a sea-level rise of about 40 cm by the 2080s, assuming increased coastal protection, 55 million people would be flooded annually in south Asia; 21 million in southeast Asia, the Philippines, Indonesia, and New Guinea; 14 million in Africa; and 3 million in the rest of the world. The relative impacts in small island states also are significant (see Section 19.3). In addition, the Atlantic coast of North and Central America, the Mediterranean, and the Baltic are projected to have the greatest loss of wetlands. Inland areas face only secondary effects—which, unlike the negative primary effects, may be either negative or positive (Yohe et al., 1996; Darwin and Tol, 2001).

Agriculture, to turn to another example, is a major economic sector in some countries and a small one in others. Agriculture is one of the sectors that is most susceptible to climate change, so countries with a large portion of the economy in agriculture face a larger exposure to climate change than countries with a lower share, and these shares vary widely. Whereas countries of the Organisation for Economic Cooperation and Development (OECD) generate about 2-3% of their GDP from agriculture, African countries generate 5-58% (WRI, 1998).

Activities at the margin of climatic suitability have the most to lose from climate change, if local conditions worsen, and the most to win if conditions improve. One example is subsistence farming under severe water stress—for instance, in semi-arid regions of Africa or south Asia. A decrease of precipitation, an increase in evapotranspiration, or higher interannual variability (particularly longer droughts) could tip the balance from a meager livelihood to no livelihood at all, and the unique cultures often found in marginal areas could be lost. An increase in precipitation, on the other hand, could reduce pressure on marginal areas. Numerous modeling studies of shifts in production of global agriculture—including Kane et al. (1992), Rosenzweig and Parry (1994), Darwin et al. (1995), Leemans (1997), Parry et al. (1999), and Darwin (1999)—have estimated that production in high-latitude countries is likely to increase and production in low-latitude countries is likely to decrease, even though changes in total global output of agriculture could be small. Results in the temperate zone are mixed. Low-latitude countries tend to be least developed and depend heavily on subsistence farming. Under current development trends they will continue to have a relatively high share of GDP in agriculture. Thus, the impacts of declines in agricultural output on low-latitude countries are likely to be proportionately greater than any gains in high-latitude countries (see Box 19-3).

Vulnerability to the health effects of climate change also differs across regions and within countries, and differences in adaptive capacity again are important. Box 19-4 notes that wealthier countries will be better able to cope with risks to human health than less wealthy countries. Risks also vary within countries, however. In a country such as the United States, the very young and the very old are most sensitive to heat waves and cold spells, so regions with a rapidly growing or rapidly aging population would have relatively large exposure to potential health impacts. In addition, poor people in wealthy countries may be more vulnerable to health impacts than those with average incomes in the same countries. For example, Kalkstein and Greene (1997) found that in the United States, residents of inner cities, which have a higher proportion of low-income people, are at greater risk of heat-stress mortality than others. Differences among income groups may be more pronounced in developing and transition countries because of the absence of the elaborate safety nets that developed countries have constructed in response to other, nonclimate stresses.

These observations underscore one of the critical insights in Chapter 18: Adaptive capacity differs considerably between sectors and systems. The ability to adapt to and cope with climate change impacts is a function of wealth, technology, information, skills, infrastructure, institutions, equity, empowerment, and ability to spread risk. The poorest segments of societies are most vulnerable to climate change. Poverty determines vulnerability via several mechanisms, principally in access to resources to allow coping with extreme weather events and through marginalization from decisionmaking and social security (Kelly and Adger, 2000). Vulnerability is likely to be differentiated by gender—for example, through the "feminization of poverty" brought about by differential gender roles in natural resource management (Agarwal, 1991). If climate change increases water scarcity, women are likely to bear the labor and nutritional impacts.

The suggested distribution of vulnerability to climate change can be observed clearly in the pattern of vulnerability to natural disasters (e.g., Burton et al., 1993). The poor are more vulnerable to natural disasters than the rich because they live in more hazardous places, have less protection, and have less reserves, insurance, and alternatives. Adger (1999), for instance, shows that marginalized populations within coastal communities in northern Vietnam are more susceptible to the impacts of present-day weather hazards and that, importantly, the wider policy context can exacerbate this vulnerability. In the Vietnamese case, the transition to market-based agriculture has decreased the access of the poor to social safety nets and facilitated the ability of rich households to overexploit mangroves, which previously provided protection from storms. Similarly, Mustafa (1998) demonstrates differentiation of flood hazards in lowland Pakistan by social group: Insecure tenure leads to greater impacts on poorer communities. See Chapter 18 for further examples. The natural disaster literature also concludes that organization, information, and preparation can help mitigate large damages at a moderate cost (e.g., Burton et al., 1993). This underscores the need for adaptation, particularly in poor countries.

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