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Subsistence agricultural production is vital to the economies, nutritional status, and social well-being of small islands—particularly the small, low-lying, atoll states where food security is a major concern. The main subsistence crops include taro, sweet potato, yam, breadfruit, bananas, coconut, and a variety of vegetables. Production of cash crops such as sugarcane, copra, coffee, cocoa, rubber, and tea (grown at higher elevations on high islands) also is important because export of these products earns valuable foreign exchange. Climate change could precipitate heat stress, changes in soil moisture and temperature, evapotranspiration, and rainfall that might affect the growth of some subsistence root crops and vegetables. The consequences of such changes for agriculture are likely to be more severe in areas that already are under stress—for example, water-scarce islands. Crop agriculture also can be affected by tropical cyclones and other extreme events, such as floods and droughts. To the extent that many small islands are susceptible to these phenomena, it is highly likely that crop production in these states would be impacted by alterations in the patterns of these events as a consequence of climate change.
On low islands and atolls in the Pacific, practically all crop agriculture is concentrated at or near the coast. Thus, changes in the height of the water table and salinization as a result of sea-level rise would be stressful for most varieties of taro and other crops, which have low tolerance for salt. It has been suggested that in general, C3 crops, which include many tropical crops, will benefit more from the effect of CO2 fertilization than C4 plants. However, recent findings indicate that the impact on sugarcane and maize yields would be adverse (Jones et al., 1999).
Singh and El Maayar (1998), using GCM (CCC 11) outputs and high, medium, and low CO2 emission scenarios coupled with a crop model (FAO) to simulate crop yields, found that sugarcane yields may decrease by 20-40% under a 2xCO2 climate change scenario in Trinidad and Tobago in the southern Caribbean. The decrease in yields is attributed to increased moisture stress caused by the warmer climate. These reductions in sugarcane yields deriving from climate change are similar to those found for maize—another C4 crop—in nearby Venezuela (Maytin et al., 1995). These results are supported by similar findings in Mauritius, which are derived from the Agricultural Production Systems Simulator Model (APSIM-Sugarcane) developed by the Agricultural Production Systems Research Unit, Australia. The study projects a decline in sucrose yield by more than 50% with a doubling of CO2 (Cheeroo-Nayamuth and Nayamuth, 1999).
Although fishing is largely artisanal or small-scale commercial, it is an important activity on most small islands and makes a significant contribution to the protein intake of island inhabitants (Blommestein et al., 1996; Mahon, 1996). The impacts of climate change on fisheries are complex and in some cases are indirect. As with other renewable resources, an assessment of climate change impacts on fisheries is complicated by the presence of anthropogenic and other non-climate-related stresses, such as habitat loss and overexploitation (Challenger, 1997).
Many breeding grounds for commercially important fish and shellfish are located in shallow waters near coasts. These areas include mangroves, coral reefs, seagrass beds, and salt ponds—all of which are likely to be affected by climate change. Generally, fisheries in the small island states are not expected to be adversely affected by sea-level rise per se. Higher sea level would be a critical factor for fisheries only if the rate of rise were far more rapid than the current succession of coastal ecosystems (e.g., mangroves, seagrasses, corals) on which some fish species depend (Everett, 1996). In tropical islands, these ecosystems function as nurseries and forage sites for a variety of important commercial and subsistence species. In this context, the unfavorable effects of higher CO2 concentrations on coral reef development, coupled with widespread coral bleaching, must be considered a significant threat in many small island states (see Section 17.2.4.1). Fish production obviously would suffer if these habitats were endangered or lost (Costa et al., 1994).
On a global scale, it is not expected that climate change and climate variability will lead to any significant reduction in fisheries production. However, important changes in the abundance and distribution of local stocks (which may be of direct concern to some small islands) are likely to occur (IPCC, 1996). For example, Lehodey et al. (1997) have shown that spatial shifts in the abundance of skipjack tuna in the Pacific are linked to the ENSO cycle. They note that catches are highest in the western equatorial Pacific warm pool, which can be displaced by as much as 50° of longitude eastward during El Niño episodes and westward in La Niña years (Lehodey et al., 1997). This must be a concern to Pacific islanders whose access to the skipjack stocks now appears to be largely controlled by the periodicity of ENSO events.
Several management strategies for minimizing the adverse effects of climate change on fish stocks have been proposed. These measures—many of which already are being implemented in some island states—include conservation, restoration, and enhancement of vital habitats such as mangroves, coral reefs, and seagrass beds; establishment and management of marine reserves and protected areas for identified critical species; and implementation of bilateral and multilateral agreements and protocols for exploitation and management of shared fisheries (migratory and straddling stocks) (IPCC, 1998; Berkes et al., 2001). Aquaculture also may be considered by island states as another means of reducing stress on wild stocks. However, great precaution must be taken to ensure that this measure does not exacerbate existing problems of habitat loss and competition for nutrients (Carvalho and Clarke, 1998; see also Section 6.6.4).
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