The climate-sensitive agricultural sector is important to the subsistence economies of many island states (SPREP, 1994a, 1994b, 1996). On many islands, agricultural production systems already are stressed as a consequnce of high population densities and growth rates. Few studies have been conducted specifically on the effects of climate change on agriculture in small islands (IPCC 1996, WG II, Section 13.6.4). However, those investigations that have been undertaken suggest that although CO2 fertilization might have a beneficial effect-mainly on C3 crops-the net effect of climate change is unlikely to be beneficial (Singh et al., 1990; Singh, 1994; SPREP, 1996).
Examination of the agricultural impacts of climate variability associated with seasonal to interannual climate phenomena offers valuable insight into the potential effects of climate change on agriculture. Climate change and climate variability effects that alter the rainfall regime, increase evaporation, or reduce soil moisture would affect agricultural production-possibly with adverse consequences for food security and nutrition in many countries. Crop yields in small island states in the Pacific are projected to decrease as a consequence of reduced solar radiation (resulting from increased cloudiness), higher temperatures (causing shorter growth duration and increased sterility in some cultivars), and changes in water availability (because of changes in the frequency of droughts and floods, as well as changes in their spatial and temporal distribution) (Singh et al., 1990). Seawater intrusion also would degrade the fertility of coastal soils and consequently contribute to a reduction in yields (IPCC 1996, WGII, Sections 13.6.4 and 13.7). Some of these adverse consequences of climate change may be partially offset, however, by the beneficial effects of increased atmospheric CO2 (SPREP, 1996).
Singh (1994) projects that, for small islands in the Pacific, an extension of the dry season by 45 days would lead to a decrease in maize yields of 30-50%. Similarly, yields from sugarcane and taro would be reduced by 10-35% and 35-75%, respectively. On the other hand, Singh et al. (1990) found that significantly increased rainfall (>50%) during the wet season on the windward side of the larger islands would cause taro yields to increase by 5-15%, but would reduce rice yields by approximately 10-20% and maize yields by 30-100%.
In Tuvalu, contraction of the freshwater lens on the atolls (as a result of
increasing water demand and sea-level rise) is expected to reduce crop yields
severely. At locations such as Funafuti atoll, where there already is heavy
demand on the water supply, the effects of sea-level rise will exacerbate water
scarcity. The crop expected to be most seriously affected is pulaka (giant taro).
Reduced yields from pulaka pits are "likely to have significant cultural ramifications,
given the central role of this crop in Tuvaluan society" (SPREP, 1996, Section
6.4.1). The cultivation of taro, another important subsistence crop in the Pacific
islands, would be similarly threatened (see Box 9-2).
The pit cultivation of taro is particularly susceptible to changes in freshwater quality. Taro is grown in depressions and pits that have been excavated down to the freshwater lens and partly filled with composting organic matter. Leaves of many species-including Guettarda speciosa, Tournefortia argentea, Artocarpus altilis, Triumfetta procumbens, and Hibiscus tiliaceus-are used to form the organic soil. In Kiribati, taro (C. Chamissonis) is planted in 20-m x 10-m pits, 2-3 m deep, with the taro corm placed in "organic baskets" of Pandanus and Cocos nucifera and anchored in holes 60 cm below the water level. In Puluwat Atoll, in contrast, the taro is planted in organic-matter bundles 0.5 m above the water level. Taro swamps also are sites of high evapotranspiration; increased loss of freshwater will increase the risk of saltwater intrusion.
A rise in sea level will have a serious impact on atoll agroforestry and the pit cultivation of taro. Erosional changes in the shoreline will disrupt populations, and the combined effects of freshwater lens loss and increased storm surges will stress freshwater plants and increase vulnerability to drought (Wilkinson and Buddemeier, 1994).
Recent research has attempted to assess changes in world prices for selected crops, based on GCM projections. Reilly et al. (1994) estimate that, under the GFDL scenario, world prices for most crop commodities would fall relative to baseline prices; the exceptions are rice and sugar, which would rise by approximately 30% and 15%, respectively. Should such a projected increase in the price of world sugar occur, positive economic benefits (in the form of increased foreign exchange earnings) would accrue to the economies of sugar-exporting small island states. The estimated price increases are somewhat less for scenarios that include adaptation. In the GISS scenario, prices for soybeans, groundnuts, cotton, and tobacco fell by about 10-15% with adaptation. Prices for other crop commodities considered in the analysis rose by as much as 20% (IPCC 1996, WG II, Section 13.8.2).
Although these scenarios do not address small island states specifically, some of the results would be relevant to any analysis of climate change impacts on agriculture in these nations. To the extent that island states depend heavily on food imports and export some agricultural products, such projected price changes would have a considerable impact on the ability of these countries to earn much-needed foreign exchange.
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