The United States (U.S.) and Canada will experience climate changes through direct effects of local changes (e.g., temperature, precipitation and extreme weather events), as well as through indirect effects, transmitted among regions by interconnected economies and migrations of humans and other species. Variations in wealth and geography, however, lead to an uneven distribution of likely impacts, vulnerabilities and capacities to adapt. This chapter reviews and synthesises the state of knowledge on direct and indirect impacts, vulnerability and adaptations for North America (comprising Canada and the U.S). Hawaii and other U.S. protectorates are discussed in Chapter 16 on Small Islands, and Mexico and Central America are treated in Chapter 13 on Latin America. Chapter 15, Polar Regions, covers high-latitude issues and peoples.

14.1.1 Key findings from the Third Assessment Report (TAR)

Key findings for the North America chapter of the Third Assessment Report (TAR) (Cohen et al., 2001) are:

Resources and ecosystems

• In western snowmelt-dominated watersheds, shifts in seasonal runoff, with more runoff in winter. Adaptation may not fully offset effects of reduced summer water availability.

• Changes in the abundance and spatial distribution of species important to commercial and recreational fisheries.

• Benefits from warming for food production in North America but with strong regional differences.

• Benefits from farm- and market-level adjustments in ameliorating impacts of climate change on agriculture.

• Increases in the area and productivity of forests, though carbon stocks could increase or decrease.

• Major role of disturbance for forest ecosystems. The forest-fire season is likely to lengthen, and the area subject to high fire danger is likely to increase significantly.

• Likely losses of cold-water ecosystems, high alpine areas, and coastal and inland wetlands.

Human settlements and health

• Less extreme winter cold in northern cities. Across North America, cities will experience more extreme heat and, in some locations, rising sea levels and risk of storm surge, water scarcity, and changes in timing, frequency, and severity of flooding.

• The need for changes in land-use planning and infrastructure design to avoid increased damages from heavy precipitation events.

• For communities that have the necessary resources, reduced vulnerability by adapting infrastructure.

• Increased deaths, injuries, infectious diseases, and stress-related disorders and other adverse effects associated with social disruption and migration from more frequent extreme weather.

• Increased frequency and severity of heatwaves leading to more illness and death, particularly among the young, elderly and frail. Respiratory disorders may be exacerbated by warming-induced deterioration in air quality.

• Expanded ranges of vector-borne and tick-borne diseases in North America but with modulation by public health measures and other factors.

Vulnerability and adaptation

• Increased weather-related losses in North America since the 1970s, with rising insured losses reflecting growing affluence and movement into vulnerable areas.

• Coverage, since the 1980s, by disaster relief and insurance programmes of a large fraction of flood and crop losses, possibly encouraging more human activity in at-risk areas.

• Responses by insurers to recent extreme events through limiting insurance availability, increasing prices and establishing new risk-spreading mechanisms. Improving building codes, land-use planning and disaster preparedness also reduce disaster losses.

• Awareness that developing adaptation responses requires a long, interdisciplinary dialogue between researchers and stakeholders, with substantial changes in institutions and infrastructure.

• Recognition that adaptation strategies generally address current challenges, rather than future impacts and opportunities.

14.1.2 Key differences from TAR

This assessment builds on the findings from the TAR and incorporates new results from the literature, including:

• Prospects for increased precipitation variability, increasing challenges of water management.

• The need to include groundwater and water-quality impacts in the assessment of water resources.

• The potential that multi-factor impacts may interact non-linearly, leading to tipping points.

• The potential importance of interactions among climate change impacts and with other kinds of local, regional and global changes.

• The potential for adaptation, but the unevenness of current adaptations.

• The challenge of linking adaptation strategies with future vulnerabilities.

• Availability of much more literature on all aspects of impacts, adaptation and vulnerability in North America.

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