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Historically, farming systems have adapted to changing economic conditions, technology, and resource availability and have kept pace with a growing population (CAST, 1992; Rosenberg, 1992). Evidence exists that agricultural innovation responds to economic incentives such as factor prices and can relocate geographically (Hayami and Ruttan, 1985; CAST, 1992). A number of studies indicate that adaptation and adjustment at all levels-but especially at the farm level-will be important to limit losses or to take advantage of improving climatic conditions (IPCC 1996, WG II, Section 13.9). Examples of technological options for adaptation by agriculture include seasonal changes in sowing dates; different crop varieties or species; new crop varieties; water supply and irrigation systems; management adjustments with fertilizer, tillage, and so forth; and improved short-term climate prediction (IPCC 1996, WG II, Section 13.9.1; Darwin et al., 1995). Socioeconomic options for adaptation include improved training and general education of populations dependent on agriculture; assessment of currently successful strategies for responding to climate variability; improved agricultural research to increase the robustness of new farming strategies; interactive communication to bring research results to farmers and farmers' problems to researchers; improved preservation and maintenance of genetic material critical to adaptation; and food programs to buffer against local supply changes. Transportation, distribution, and market integration provide additional flexibility for regions to respond to climate variability, and changes in policies could increase the adaptive capacity of agriculture (IPCC 1996, WG II, Section 13.9.2).
Recent analyses of issues of long-run sustainability associated with agricultural adaptation to climate change from arbitrary doubling of equivalent CO2 concentrations have concluded that there is considerably more sectoral flexibility and adaptation potential than was found in earlier analyses.
Schimmelpfenning et al. (1996) concluded that the costs and benefits of climate change cannot be adequately evaluated independent of behavioral, economic, and institutional adjustments required by changing climate. Smit et al. (1996) and Brklacich et al. (1997b), in their research into agricultural adaptation to climatic variability and change in Ontario, reached a similar conclusion and urged that future research into agriculture and climatic change be reframed to explicitly consider agricultural decision making and adaptation processes. Although scientific controversy remains over the nature and rate of climate change and the importance of climate variability, most scenarios suggest gradual changes in mean temperature and precipitation over decades, providing opportunities for farms and other parts of the sector to adapt. In addition, the time scale of 80-100 years makes other profound social changes inevitable. Income and population growth and technological innovation will accelerate or decelerate, depending on global location, at the same time that adaptation to climate is taking place. Social and cultural factors may influence the rate at which adaptation measures are implemented within some subregions of North America. There may be time lags between decisions to follow an adaptive strategy and subsequent adjustments in the agricultural system. The costs and time required for such adjustments in infrastructure will need to be considered in planning adaptation options. Although none of these factors can be considered in isolation, recent research shows that the negative effects of climate change on agriculture probably are overestimated by studies that do not account for economic adjustments or consider the broader economic and environmental implications of such changes. However, uncertainties remain about the implications of changes in climate variability, as well as crop responses to increases beyond a doubling of equivalent atmospheric CO2 concentrations.
Vulnerability to climate change-induced hunger or severe economic distress for the overall economy of North America as a result of climate change impacts on the agricultural sector is relatively low.
The United States and Canada have high GNP per capita; the agricultural population is a small share of the total population; and agriculture is, in general, a small share of the economy. These areas are important for world food production. Midcontinental areas of the United States and Canada are prone to drought, which would be exacerbated if climate change reduced moisture availability or increased the demand for water (as occurs in several GCM scenarios). Economic dislocation is likely to be limited to the agricultural sector or to subregions highly dependent on agriculture (IPCC 1996, WG II, Section 13.7). Evidence suggests that yields of crops grown at the margin of their climatic range or in climates where temperature or precipitation could easily exceed threshold values during critical crop growth periods are more vulnerable (Matthews et al., 1994a,b; IPCC 1996, WG II, Section 13.7). A regional economy that offers only limited employment alternatives for workers dislocated by the changing profitability of farming is relatively more vulnerable than those that are economically diverse. As an example, the Great Plains area of North America is most dependent on agriculture and thus might be the most economically vulnerable to climate change (Rosenberg, 1993).
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