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Housing, industry, commerce, and the major components of infrastructure that support settlements-energy, water supply, transportation, waste disposal, and so forth-have varying degrees of vulnerability to climate change. They can be affected directly through projected changes in climate (temperature, precipitation, etc.) and indirectly through projected impacts on the environment, natural resources, and agriculture. Indirect pathways to impacts include expected changes in the availability of natural resources, geographic shifts in climate-sensitive resource industries, effects on environmental quality and health from changes in ecosystems, and other effects resulting from changes in environmental service functions. Furthermore, these effects on human settlements in theory could lead to tertiary impacts-such as altering land use and redistributing population and activities to other regions-resulting in further changes in natural resources and other activities. Such effects, however, are largely speculative at the current state of knowledge.
Climate directly affects the quality of life; alters patterns of settlement and human activities; subjects humans to risks to their health, safety, and property (e.g., due to extreme events); and, therefore, has costs and benefits for individuals and for the private and public sectors. As such, changes in climate are expected to have positive and negative impacts.
Climate change will have direct impacts on economic activity in the industry, energy, and transportation sectors; impacts on markets for goods and services; and impacts on natural resources on which economic activity depends. Activities directly sensitive to climate include construction, transportation, offshore oil and gas production, manufacturing dependent on water, tourism and recreation, and industry that is located in coastal zones and permafrost regions. Activities with markets sensitive to climate include electricity and fossil fuel production for space heating and air conditioning, construction activity associated with coastal defenses, and transportation. Activities dependent on climate-sensitive resources include agro-industries (food/drink, forestry-related activity, and textiles), biomass production, and other renewable energy production.
Impacts occurring in the distant future are difficult to predict in detail because the context of human settlement patterns and technologies cannot be forecast accurately. Concomitantly, there are substantial opportunities for adaptation to changed climates in conjunction with the development of future housing and infrastructure facilities, depending in part on our capability to forecast climate changes. Many types of impacts on human facilities have the potential to be partially or completely reduced or eliminated through adaptation, though this usually will increase their costs.
Projected changes in climate will have both negative and positive impacts on the operation and maintenance costs of transportation systems.
Studies in temperate and northern climates generally have indicated that higher temperatures will result in lower maintenance costs, especially with fewer freeze-thaw cycles and less snow (e.g., Walker et al., 1989; Daniels et al., 1992). Black (1990) points out, however, that increased pavement buckling caused by longer periods of intense heat is a possibility. Lewis (1988) and Hirsch (1988) cite such cases from the great North American summer heat wave of 1988.
In moderate climates, water transport would be affected by changes in river navigability. Reductions in rainfall, which are possible during the summer in mid-latitudes in North America, could adversely affect waterborne transportation. During the 1988 drought, industries that relied on bulk transportation of raw materials and finished products by barge on the Mississippi River found that low water kept more than 800 barges tied up for several months. In 1993, by contrast, floods in the upper Mississippi valley also disrupted the barge transportation system, and in 1997 increased siltation associated with floods prevented ships from reaching the port of New Orleans for several days. To the extent that industry is moving toward just-in-time production systems, it will become more vulnerable to interruptions for these and other reasons.
In colder regions, the most significant direct impact of warming is likely to be on inland and coastal water transportation. A longer season for Arctic shipping is likely for locations like Prudhoe Bay, Alaska, which depends on the short ice-free season to barge in modular loads too large to go by truck. Increased wave activity and increased frequency of extreme weather events might have a more significant effect on coastal transportation operations, but little research has been conducted on this topic. A survey of the potential impacts on Canadian shipping suggested net benefits to Arctic and ocean shipping as a consequence of deeper drafts in ports and longer navigational seasons (IBI Group, 1990).
Winter roads on ice constitute an important part of the transportation network in parts of Canada's north. For example, about 10-15% of the total annual flow of goods in the Mackenzie Valley moves over winter roads, some of which cross major rivers. As the name implies, winter roads (or ice roads) are functional in the winter only; they are made of snow, ice, or a mixture of soil and snow/ice and can be created on the frozen surface of lakes and rivers. Lonergan et al. (1993) found a substantial reduction in the length of the "ice road" season based on climate change projections.
Further south, there would be a greater number of ice-free days for inland waterways such as the Great Lakes and St. Lawrence Seaway (IBI Group, 1990). Inland waterways, however, may suffer loss of depth from greater periods of seasonal drought, reducing their usefulness for commercial shipping even if the ice-free season is lengthened (Black, 1990). A similar study showed that reduced ice cover compensated for lower water levels in two of three climate change scenarios but that dredging costs generally increased in the six Great Lakes ports examined (Keith et al., 1989). Other climate impacts could arise from changes in snowfall or melting of the permafrost (IBI Group, 1990).
Changes in the location and nature of agricultural activities, as well as other climate-dependent industries, could have a large impact on the freight transport system.
Existing assessments of transportation impacts have recognized the potential significance of changes in geographical patterns of economic activity on the transportation network. Black (1990) notes that even gradual, long-term global warming could cause a major disruption of the movement of goods and people in North America. The IBI Group (1990) suggests that there probably would be a northward spreading of agricultural, forestry, and mining activities-resulting in increased population and intensified settlement patterns in Canada's mid-north and even in Arctic areas. Marine, road, rail, and air links would have to be expanded accordingly.
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