Humans live in a wide variety of settlements, ranging from hunter-gatherer camps and villages of a handful of families to modern megacities and metropolitan regions of tens of millions of inhabitants. Settlement economic and social structure�and the components of infrastructure that support settlements: energy, water supply, transportation, drains, waste disposal, and so forth�have varying degrees of vulnerability to climate change and generally are evolving far more quickly than the natural environment. Settlements can be affected directly through changes in human health and infrastructure and indirectly through impacts on the environment, natural resources, and local industries such as tourism or agriculture. Furthermore, these effects on human settlements theoretically could lead to tertiary impacts such as altered land use, redistribution of population and activities to other regions, and altered trade patterns among regions, resulting in still further changes in natural resources and other activities. Tertiary effects, however, are largely speculative at the current state of knowledge. Some of these tertiary effects could be either positive or negative at the regional level.

This chapter builds on Chapters 11 and 12 of the IPCC Second Assessment Report (IPCC, 1996), and on the findings in the Special Report on Regional Impacts of Climate Change (RICC) (IPCC, 1998). The SAR identifies the most vulnerable types of communities, many examples of which are documented in RICC. The SAR states that the most vulnerable communities are not only poorer coastal and agrarian communities in arid areas identified in the First Assessment Report in 1990; they also include a great variety of settlements, most of them informal or illegal and with a predominance of low-income residents, built on hazardous sites such as wetlands or steep hillsides in or around many urban areas in the developing world.

The SAR and RICC also identify two categories of climate-sensitive industries. Sectors with activities that are sensitive to climate include construction, transportation operations and infrastructure, energy transportation and transmission, offshore oil and gas, thermal power generation, water availability for industry, pollution control, coastal-sited industry, and tourism and recreation. Sectors in which economic activity is dependent on climate-sensitive resources are agroindustry, biomass, and other renewable energy.

The SAR notes that infrastructure typically is designed to tolerate a reasonable level of variability within the climate regime that existed when it was designed and built. However, climate change could affect both average conditions and the probability of extreme events.

This Third Assessment Report (TAR) confirms most of these conclusions. However, the analyses in the SAR and RICC are concerned mostly with identifying and documenting potential effects. The TAR assesses their relative importance and the certainty/confidence of the conclusions reached.

Although literature published since the SAR was issued has not changed the catalog of potential impacts, much more has been learned about the quantitative details of many of the effects, which are being studied more systematically than was true 5�10 years ago. The results are becoming somewhat more quantitative, and it is becoming possible to assign confidence ratings to many of the effects for the first time. More also is known concerning adaptation options. It is now possible to describe many of the options more quantitatively and in the context of development, sustainability, and equity (see Munasinghe, 2000). Energy, industry, and infrastructure are treated as part of settlements in the TAR.

Human settlements integrate many climate impacts initially felt in other sectors and differ from each other in geographic location, size, economic circumstances, and technical, political, institutional, and social capacities. Climate affects human settlements by one of three major pathways, which provides an organizational structure for the settlements effects discussion in this chapter:

1. Changes in productive capacity (e.g., in agriculture or fisheries) or changes in market demand for goods and services produced in settlements (including demand from those living nearby and from tourism). The importance of this impact depends on the range of economic alternatives. Rural settlements generally depend on one or two resources, whereas urban settlements usually (but not always) have a broader array of alternative resources. Impacts also depend on the adaptive capacity of the settlement, which in turn depends on socioeconomic factors such as the wealth, human capital, and institutional capability of the settlement.
   
2. Physical infrastructure or services may be directly affected (e.g., by flooding). Concentration of population and infrastructure in urban areas can mean higher numbers of persons and value of physical capital at risk, although there also are many economies of scale and proximity that help to assure well-managed infrastructure and provision of services such as fire protection and may help reduce risk. Smaller settlements (including villages and small urban centers) and many larger urban centers in Africa and much of Asia, Latin America, and the Caribbean often have less wealth, political power, and institutional capacity to reduce risks in this way.
   
3. Populations may be directly affected through extreme weather, changes in health status, or migration. Extreme weather episodes may lead to changes in deaths, injuries, or illness. Health status may improve as a result of less cold stress, for example, or deteriorate as a result of more heat stress and disease.

The discussion of impacts on human settlements, energy, and industry that follows begins with a discussion of nonclimate trends that affect settlements. The discussion then assesses potential impacts of climate change on three general types of settlements: resource-dependent settlements; riverine, coastal, and steeplands settlements; and urban settlements. This discussion is followed by a discussion of impacts on the energy sector and industries that may be particularly affected by climate change and an assessment of potential impacts on infrastructure. The chapter next discusses management and adaptation issues and integration of impacts across sectors, and it closes with a review of science and information needs.

IPCC Homepage