Climate Change 2001:
Working Group II: Impacts, Adaptation and Vulnerability
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7.2. State of Knowledge Regarding Climate Change Impacts on Human Populations

The TAR differs from the two previous assessments in that the literature has begun to quantify several of the climate-related risks to human settlements that previously were identified only in qualitative terms. Additional attention and research has been devoted to adaptation mechanisms that provide resistance to climate-related impacts and ability to recover from them. Several economic and social trends that are specific to development and change in human settlements will interact with the effects of climate change in the future and may exacerbate or mitigate the effects of climate change alone.

7.2.1. Nonclimate Trends Affecting Vulnerability to Climate

Population growth: Except for parts of Europe and the Russian Federation, most regions are expected to experience population growth. Although Special Report on Emission Scenarios (SRES) marker scenarios in Chapter 3 do not span the entire realm of possibilities and have not been assigned probabilities, they do show that under plausible conditions, future regional population growth rates will range from modest (Europe and North America, where projected rates are just above or below replacement) to 3% or more (portions of Latin America and especially Africa).

Urbanization (proportion of population living in urban areas) is expected to continue, especially in the developing world. Close to half of the world’s population now lives in urban areas, and the likely trend toward a more urban world means that the impacts of climate change on human settlements, if they occur, increasingly will affect urban populations. The most rapid urban growth rates are occurring in the developing world, where urban populations are estimated to be growing at 2.7% yr-1, compared to 0.5% yr-1 in more developed regions (UN, 2000). There also is a growing concentration of population in cities with more than 1 million inhabitants. The number of such cities worldwide grew from 80 in 1950 to more than 300 by 1990 and is expected to exceed 500 by 2010 (UNCHS, 1996; UN, 2000). Most cities with more than 1 million inhabitants are now in the developing world, although—as in more developed regions—they are heavily concentrated in its largest economies (UNCHS, 1996). Cities also are reaching unprecedented sizes. However, the future world may be less dominated by “megacities” (cities of more than 10 million population) than previously predicted. Megacities are likely to be smaller than previously predicted and still contain a small proportion of the world’s population—less than 4% in 1990, the last date for which there is census data for most nations (UNCHS, 1996; UN, 2000). Most of the world’s urban population live in the 40,000–50,000 urban centers with fewer than 1 million inhabitants (UNCHS, 1996). In 1990, cities with more than 1 million inhabitants had just more than one-third of the world’s urban population and just more than one-seventh of its total population (UN, 2000). Urban population increases were particularly sharp in the second half of the 20th century in some regions where urbanization had been held down by policy, such as China (Institute of Land Development and Regional Economy, State Planning Committee, 1998). Trends toward urbanization mean that the impacts of climate change on human settlements in most countries, if they occur, increasingly will affect urban populations, not rural or traditional settlements.

Table 7-1: Impacts of climate change on human settlements, by impact type and settlement type (impact mechanism). Typeface indicates source of rating: Bold indicates direct evidence or study; italics indicates direct inference from similar impacts; and plain text indicates logical conclusion from settlement type, but cannot be directly corroborated from a study or inferred from similar impacts. Impacts generally are based on 2xCO2 scenarios or studies describing the impact of current weather events (analogs) but have been placed in context of the IPCC transient scenarios for the mid- to late 21st century.
Type of Settlement, Importance Rating, and Reference
 
Resource-Dependent
(Effects on Resources)
Coastal-Riverine-Steeplands
(Effects on Buildings and Infrastructure)
Urban 1+ M
(Effects on Populations)
Urban <1 M (Effects on Populations)
 
   
Impact
Type
Urban,
High
Capacity 		Urban,
Low
Capacity 		Rural,
High
Capacity 		Rural,
Low
Capacity 		Urban,
High
Capacity 		Urban,
Low
Capacity 		Rural,
High
Capacity 		Rural,
Low Capacity 		High
Capacity 		Low
Capacity 		High
Capacity 		Low Capacity Confidence
Flooding, landslides L–M1 M–H2 L–M1 M–H2 L–M1 M–H2 M–H1 M–H2 M1 M–H2 M1 M–H2 H
Tropical cyclone L–M3 M–H4 L–M3 M–H4 L–M3 M–H4 M3 M–H4 L–M3 M4 L3 L–M4 M
Water quality L–M M L–M M–H L–M5 M–H6 L–M M–H L–M M–H L–M M–H M
Sea-level rise L–M7 M–H6 L–M7 M–H6 M8 M–H9 M M–H6 L8 L–M6 L L–M6 H (L for resource-dependent)
Heat/cold waves L–M M–H L–M M–H L–M10 L–M L–M10 L L–M10 M–H11 L–M10 M–H11 M (H for urban)
Water shortage L12 L–M M12 M–H13 L L–M L–M M–H L M L–M12 M M (L for urban)
Fires L–M L–M L–M14 M–H L–M L–M L–M L–M L–M15 L–M16 L–M M VL (M for urban)
Hail, windstorm L–M17 L–M18 L–M17 M–H18 L–M L–M L–M M L–M17 L–M18 L–M17 L–M18 L
Agriculture/ forestry/fisheries productivity L–M19 L–M20 L–M M–H L L L L L L–M L–M M L
Air pollution L–M21 L–M L L — — — — L–M10 M–H22 L–M10 M–H22 M
Permafrost melting L L L–M23 L–M L L L23 L — — L–M L–M H
Heat islands L L — — L L — — M24 L–M24 L–M25 L–M25 M
Table 7-1 Notes
1. Changnon (1996b), Yohe et al. (1996), Evans and Clague (1997), FEMA (1997), Smith et al. (1999); 2. Choudhury (1998), Rosquillas (1998), Magaña (1999); 3. Landsea et al. (1996), Pielke (1996), Pielke and Landsea (1998); 4. Yohe et al. (1996), Hurricane Mitch cost Honduras 80% of its GDP and Nicaragua 49% (FAO, 1999), Swiss Re (1999); 5. in general, wealthier areas substitute new locations from which to draw water (WG2 SAR Section 10.5.4; Changnon and Glantz, 1996; Arnell, 1998); 6. Meehl (1996), Nicholls and Hoozemans (1996), Nicholls and Mimura (1998); 7. Mimura et al. (1998); 8. FEMA (1991), Scott (1996), Rosenzweig and Solecki (2000); 9. Ren (1994), Nicholls et al. (1999), see also Chapters 6 and 11; 10. Phelps (1996), Chestnut et al. (1998), Duncan et al. (1999), Kerry et al. (1999); 11. despite acclimatization, Indian cities have lost dozens to hundreds of people to heat-related deaths in recent years—more than 1,300 in 1998 (De and Mukhopadhyay, 1998); 12. Wheaton and Arthur (1989), Rosenberg (1993), Lettenmaier et al. (1998), Gleick (2000); 13. Meehl (1996), Scott (1996), Lewis et al. (1998); 14. Hirsch (1999); 15. the 1991 Oakland Hills and the 1994 Sydney fires are examples of losses sustained at urban interface in developed countries [in Oakland, a wildfire destroyed approximately 600 ha and more than 2,700 structures in the hills surrounding East Bay, took 25 lives, and caused more than US$1.68 billion in damages (see , sponsored by the U.S. Forest Service); in the Sydney area, 800,000 ha burned, more than 200 houses—mostly in urban areas—were destroyed, and two firefighters and two civilians were killed (see Australian National University’s FIRENET Web site)]; 16. EEPSEA (2000), Wheeler (2000); 17. Andrey and Mills (1999), Dorland et al. (1999), Changnon (2000); 18. for example, on the Indian subcontinent on 26 April 1989, a single severe storm—locally known as “nor’westers” or kal’boishakhi—and a tornado north of Dhaka killed 1,300 and injured 12,000; 19. Rosenberg (1993); 20. Meltzoff et al. (1997); 21. Scott (1996); 22. WRI (1999); 23. Cohen (1997), Andrey and Mills (1999); 24. Quattrochi (1996), Chestnut et al. (1998); 25. Jáuregui (1997), Chestnut et al. (1998), Lam (1999).

Poverty is becoming increasingly urbanized, as a growing proportion of the population suffering from absolute poverty lives in urban areas. In more developed regions and in much of Latin America (e.g., 36% in Latin America—ECLAC, 2000), poverty is concentrated in urban areas. In other regions, the number of rural poor still exceeds the number of urban poor, although the proportion of absolute poor living in urban areas is growing. In addition, the scale and depth of urban poverty frequently is underestimated, in part because official income-based poverty lines are set too low in relation to the cost of living (or the income needed to avoid deprivation) in most urban centers and in part because no provision is made to include housing conditions, access to services, assets, and aspects of social exclusion within most government poverty definitions (Satterthwaite 1997). Where it occurs, urban poverty reduces the capacity of urban populations to take action to adapt to climate change; poverty also may exacerbate many of its effects.

Market systems and privatization increasingly are being used to provide new infrastructure and maintain older systems (World Bank, 1994), giving government a smaller direct role in providing infrastructure for energy, environmental residuals, communications, and other key urban services. Governments that are trying to adapt settlements to climate change increasingly may have to work indirectly through markets and regulation of private providers to adapt buildings and infrastructure to climate change.

Energy systems are changing in some places, helping to determine which mechanisms are salient in human settlements impacts (Schipper and Meyers, 1992; Hall et al., 1993; World Energy Council, 1993a):

Transportation activity and associated energy consumption are growing very rapidly in nearly every region. Except for economies in transition, the amount of goods traveling by road increased between 1990 and 1996. The increases were 50% or more, and total paved roadways worldwide rose from 39 to 46% of the total (World Bank, 1999). In all Organisation for Economic Cooperation and Development (OECD) countries, car ownership continues to rise steadily, but much of the growth in vehicle ownership is expected in developing countries and transition economies—especially in east Asia and the Pacific, and especially in urban areas (World Resources Institute, 1996). This trend contributes to local air pollution (which can be exacerbated by warm weather episodes) and to greenhouse gas (GHG) emissions.

A poleward intensification of agricultural, forestry, and mining activities is occurring, resulting in increased population and intensified settlement patterns in Canada’s mid-north, for example, and even in arctic areas. Climate change could profoundly affect settlements in these regions, if climate change is greater toward the poles (Cohen, 1997). For example, some arctic and subarctic activities such as mining depend on snow roads, which would have to be replaced with more conventional transport.

Impact of urban wealth: Many of the worst city-level problems—such as sanitation and water supply—have been addressed in high-income cities such as those in Europe and North America, but not in many developing world cities (WHO, 1992; Hardoy et al., 2000; McGranahan and Satterthwaite, 2000). A wealthy city can more easily afford the public finance and administration required to regulate more perceptible forms of pollution than a poor one. However, although the ambient environment of high-income cities may be more benign in terms of health impacts of pollution, these cities exert a far greater toll on the regional and global environment (UNCHS, 1996).


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