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* These are obviously speculative (projections based largely on extrapolating past trends) and, since any nation's or region's level of urbanisation is strongly associated with their per capita income, economic performance between 2000 and 2030 will have a strong influence on the extent to which regional populations continue to urbanise. Source: taken from or derived from statistics in United Nations (2006).

* These are obviously speculative (projections based largely on extrapolating past trends) and, since any nation's or region's level of urbanisation is strongly associated with their per capita income, economic performance between 2000 and 2030 will have a strong influence on the extent to which regional populations continue to urbanise. Source: taken from or derived from statistics in United Nations (2006).

Features of development relevant to adaptation, such as access to resources, location and institutional capacity, are likely to be predominantly urban and to be determined by differences in economic growth and access to assets, which tend to be increasingly unequal (e.g., the income gap between the richest and the poorest 20% of the world population went from a factor of 32 to 78 between 1970 and 2000: UN-Habitat, 2003). It is estimated that one third of the world's urban population (923.9 million) live in "overcrowded and unserviced slums, often situated on marginal and dangerous land" (i.e., steep slopes, food plains, and industrial zones), and that 43% are in developing countries (UN-Habitat, 2003). It is projected that in the next 30 years "the total number of slum dwellers will increase to about 2 billion, if firm and concrete action is not taken" (UN-Habitat, 2003).

Risk-prone settlements such as in coastal areas are expected to experience not only increases in weather-related disasters (CRED, 2005) but also major increases in population, urban area and economic activity, especially in developing countries (Chapter 6). Growing population and wealth in exposed coastal locations could result in increased economic and social damage, both in developing and developed countries (Pielke et al., 2005; Box 7.4).

Global economic growth projections in SRES and SRES-derived scenarios (Chapter 2) vary significantly - more than population projections. Under low-growth scenarios (A2 and B2), world GDP would double by 2020 and increase more than 10-fold by 2100. Under a high-growth scenario (A1), world GDP would nearly triple by 2020 and grow over 25-fold by 2100. Under all these scenarios, more valuable assets and activities are likely to become exposed to climate risks, but it is assumed that the economic potential to respond will also vastly increase. Economic development will be central to adaptive capacity (Toth and Wilbanks, 2004). SRES scenarios also assume convergence of national per capita incomes, which is contrary to historical tendencies for income gaps between the rich and the poor to increase. While the ratio of per capita incomes in developed as compared with developing countries stood at 16.1 in 1990, SRES scenarios assume a narrowing of this ratio to between 8.4 and 6.2 in 2020, and between 3.0 and 1.5 in 2100. Smaller differences in relative incomes are likely to have important consequences for the perception of climate vulnerability and for the pattern of response.

Because it is potentially highly dynamic, the treatment of technology varies greatly between global scenario exercises. For instance, three qualitatively-different technology scenarios were developed for SRES scenario A1 alone (A1FI, A1T and A1B). An even broader universe of technological change scenarios can be developed for global and downscaled national, regional and sectoral scenarios (e.g., Berkhout and Hertin, 2002). In this chapter we make no specific assumptions about the rate and direction of technological change into the future, recognising that very wide ranges of potentials will exist at the local and organisational levels at which climate vulnerability and responses will often be shaped, and also that the knowledge base referenced in the chapter reflects a range of assumptions about future trends. Governance is likewise a topic about which different scenario families make divergent assumptions. The SRES scenarios include both globally-integrated systems of economic and political and sustainability governance, as well as more fragmented, regionalised systems. The Global Scenarios Group set of scenarios include characterisations in which institutions and governance as we know them persist with minor reform; 'barbarisation' scenarios consider futures in which "absolute poverty increases and the gap between rich and poor ... [and] national governments lose relevance and power relative to transnational corporations and global market forces." (Gallopin et al., 1997); 'great transitions' scenarios contain storylines in which sustainable development becomes an organising principle in governance. In this chapter we also have made no specific assumptions about the nature of future pattern of governance, while recognising that institutional capacity will be central to adaptive capacity (Section 7.6.5; also see Chapter 2).

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