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 effectswhich, unlike the negative primary effects, may be either negative or positive (Yohe et al., 1996; Darwin and Tol, 2001).
Box 19-3. The Impact of Climate Change on Agriculture
The pressures of climate change on the world's food system are better understood than most other impacts. Research has focused on crop yields; on the basis of those insights, many studies also look at farm productivity, and a smaller number look at national and international agricultural markets.
Climate change is expected to increase yields at higher latitudes and decrease yields at lower latitudes. Changes in precipitation, however, also can affect yields and alter this general pattern locally and regionally. Studies of the economic impact of this change (in all cases, climate change associated with 2xCO2) conclude that the aggregated global impact on the agricultural sector may be slightly negative to moderately positive, depending on underlying assumptions (e.g., Rosenzweig and Parry, 1994; Darwin, 1999; Parry et al., 1999; Mendelsohn et al., 2000). Most studies on which these findings are based include the positive effect of carbon fertilization but exclude the negative impact of pests, diseases, and other disturbances related to climate change (e.g., droughts, water availability). The aggregate also hides substantial regional differences. Beneficial effects are expected predominantly in the developed world; strongly negative effects are expected for populations that are poorly connected to regional and global trading systems. Regions that will get drier or already are quite hot for agriculture also will suffer, as will countries that are less well prepared to adapt (e.g., because of lack of infrastructure, capital, or education). Losses may occur even if adaptive capacity is only comparatively weak because trade patterns will shift in favor of those adapting best. Overall, climate change is likely to tip agriculture production in favor of well-to-do and well-fed regionswhich either benefit, under moderate warming, or suffer less severe lossesat the expense of less-well-to-do and less well-fed regions. Some studies indicate that the number of hungry and malnourished people in the world may increase, because of climate change, by about 10% relative to the baseline (i.e., an additional 80-90 million people) later in the 21st century (e.g., Parry et al., 1999).
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 stressfor 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 agricultureincluding 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 genderfor 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
Box 19-4. The Health Impacts of Climate Change
Global climate change will have diverse impacts on human healthsome positive, most negative. Changes in the frequency and intensity of extreme heat and cold, floods and droughts, and the profile of local air pollution and aeroallergens will directly affect population health. Other effects on population health will result from the impacts of climate change on ecological and social systems. These impacts include changes in infectious disease occurrence, local food production and nutritional adequacy, and the various health consequences of population displacement and economic disruption. Health impacts will occur very unevenly around the world. In general, rich populations will be better protected against physical damage, changes in patterns of heat and cold, introduction or spread of infectious diseases, and any adverse changes in world food supplies.
The geographic range and seasonality of various vector-borne infectious diseases (spread via organisms such as mosquitoes and ticks) will change, affecting some populations that currently are at the margins of disease distribution. The proportion of the world's population living in regions of potential transmission of malaria and dengue fever, for example, will increase. In areas where the disease currently is present, the seasonal duration of transmission will increase. Decreases in transmission may occur where precipitation decreases reduce vector survival, for example.
An increased frequency of heat waves will increase the risk of death and serious illness, principally in older age groups and the urban poor. The greatest increases in thermal stress are forecast for mid- to high-latitude (temperate) cities, especially in populations with limited air conditioning. Warmer winters and fewer cold spells, because of climate change, will decrease cold-related mortality in many temperate countries. Basic research to estimate the aggregate impact of these changes has yet been limited largely to the United States and parts of Europe. Recent modeling of heat-wave impacts in 44 U.S. urban populations, allowing for acclimatization, suggests that large U.S. cities may experience, on average, several hundred extra deaths per summer. Although the impact of climate change on thermal stress-related mortality in developing country cities may be significant, there has been little research in such populations.
For each anticipated adverse health impact, there is a range of social, institutional, technological, and behavioral adaptation options that could lessen that impact. The extent to which health care systems will have the capacity to adopt them is unclear, however, particularly in developing countries. There is a basic and general need for public health infrastructure (programs, services, surveillance systems) to be strengthened and maintained. The ability of affected communities to adapt to risks to health also depends on social, political, and economic circumstances.
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