Almost without exception, small island states have been shown to be at great risk from projected impacts of climate change, particularly sea-level rise. The projected global rate of rise of 5 mm yr^-1 (±2-9 mm yr^-1 ) is two to four times greater than the rate experienced in the previous 100 years (IPCC, 1998). Many of these islands rarely exceed 3-4 m above present mean sea level; even on the higher islands, most of the settlements, economic activity, infrastructure, and services are located at or near the coast.

Reliable instrumental records indicate that on average, Caribbean islands have experienced an increase in temperature exceeding 0.5°C since 1900. During the same period, there has been a significant increase in rainfall variability, with mean annual total rainfall declining by approximately 250 mm. For Pacific islands, the post-1900 temperature increase has been slightly lower than in the Caribbean: less than 0.5°C. In the case of rainfall, no clear trend emerges from the record, which shows decadal fluctuations of ±200 mm and 50-100 mm for mean annual and mean seasonal totals, respectively (IPCC, 1998).

Given the strong influence of the ocean on the climate of islands, and based on projected warming of the oceans (1-2°C for the Caribbean Sea and Atlantic, Pacific, and Indian Oceans) with a doubling of carbon dioxide (CO₂), small islands in these regions are expected to continue to experience moderate warming in the future. Under a similar scenario, mean rainfall intensity also is projected to increase by 20-30% over the tropical oceans, where most small island states are located. However, a decrease in mean summer precipitation over the Mediterranean Sea, where the small islands of Malta and Cyprus are located, is projected (IPCC, 1998).

Based on these projections, certain marine and coastal ecosystems are most likely to be adversely affected. Corals—many species of which currently exist near the upper limits of their tolerance to temperature—are projected to experience more frequent bleaching episodes as a result of elevated sea surface temperatures (SSTs). Bleaching therefore will pose a distinct threat to the productivity and survival of these valuable ecosystems (Wilkinson, 1996; Brown, 1997a,b; CARICOMP, 1997; Woodley et al., 1997). On some islands, mangroves also are expected to be threatened by the impacts of climate change. Where the rate of sedimentation is slower than the projected rate of sea-level rise and where mangroves cannot naturally adapt and migrate landward, the vulnerability of these ecosystems will increase (IPCC, 1996, 1998). In some cases, the natural resilience of these ecosystems already has been impaired by anthropogenic stresses; thus, their capacity to cope with an additional stressor such as climate change will be further compromised.

Sea-level rise poses by far the greatest threat to small island states relative to other countries. Although the severity of the threat will vary from island to island, it is projected that beach erosion and coastal land loss, inundation, flooding, and salinization of coastal aquifers and soils will be widespread. Moreover, protection costs for settlement, critical infrastructure, and economic activities that are at risk from sea-level rise will be burdensome for many small island states. Similarly, tourism—the leading revenue earner in many states—is projected to suffer severe disruption as a consequence of adverse impacts expected to accompany sea-level rise (Teh, 1997; IPCC, 1998).

Small island states are by no means a homogeneous group of countries. They vary by geography; physical, climatic, social, political, cultural, and ethnic character; and stage of economic development. Yet they tend to share several common characteristics that not only identify them as a distinct group but underscore their overall vulnerability in the context of sustainable development (Maul, 1996; Leatherman, 1997). These common characterists include the following:

• Limited physical size, which effectively reduces some adaptation options to climate change and sea-level rise (e.g., retreat; in some cases entire islands could be eliminated, so abandonment would be the only option)
  
• Generally limited natural resources, many of which already are heavily stressed from unsustainable human activities
  
• High susceptibility to natural hazards such as tropical cyclones (hurricanes) and associated storm surge, droughts, tsunamis, and volcanic eruptions
  
• Relatively thin water lenses that are highly sensitive to sea-level changes
  
• In some cases, relative isolation and great distance to major markets
  
• Extreme openness of small economies and high sensitivity to external market shocks, over which they exert little or no control (low economic resilience)
  
• Generally high population densities and in some cases high population growth rates
  
• Frequently poorly developed infrastructure (except for major foreign exchange-earning sectors such as tourism)
  
• Limited funds and human resource skills, which may severely limit the capacity of small islands to mitigate and adapt to the effects of climate change.

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