The Regional Impacts of Climate Change

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Executive Summary

Introduction

All of the small island states considered in this report are located within the tropics, with the exception of Malta and Cyprus in the Mediterranean. About one-third of the states comprise a single main island; the others are made up of several or many islands. Although some states are experiencing relative declines in sea level, others-primarily low-lying island states and atolls-are especially vulnerable to climate change and associated sea-level rise because, in many cases (e.g., The Bahamas, Kiribati, Maldives, Marshall Islands), much of the land area is only 3-4 m above the present mean sea level. Islands at higher elevations also are vulnerable-particularly in coastal zones, where settlements, economic infrastructure, and vital services tend to be concentrated.

Regional Characteristics

The ocean exerts a strong influence on small islands. Island climate is moderated by the maritime influence-which, given the islands' mainly tropical location, results in uniformly high temperatures (20C and above) throughout the year. However, other climate variables often exhibit distinct seasonal patterns-particularly rainfall distribution, which results in wet and dry seasons. Some small island states are subject to tropical cyclones (i.e., hurricanes or typhoons); those that are outside the main storm tracks also are affected by high seas and swells associated with such events. In the Pacific, large interannual rainfall variations resulting from the El Nio-Southern Oscillation (ENSO) phenomenon are an important climate characteristic; ENSO effects also are felt on islands in the Caribbean Sea and Indian Ocean.

Economic activities in small island states frequently are dominated by agriculture (e.g., sugar and bananas for export; subsistence farming for local consumption) and by tourism, both of which are sensitive to external forces and are strongly influenced by climatic factors. Fisheries, although largely artisanal, also support an important economic activity. Although total population numbers are low, settlements commonly are concentrated in the capital city or on the capital island, where population densities often are very high. Human demands on coastal and marine resources are continuing to increase; the potential impacts of climate change, added to these pressures, almost certainly will result in the degradation or loss of some natural ecosystems that are important to the economies of small island states.

Observed Climate Trends

Caribbean islands experienced an increase in mean annual temperature of more than 0.5C during the period 1900-1995. During the same period, mean annual total rainfall decreased by about 250 mm, though throughout the rainfall record has been characterized by large variability. In the Pacific islands, the increase in average annual temperature has been less than 0.5C since 1900. Rainfall records for the Pacific (1900-1995) reveal no clear trend; they show decadal fluctuations of 200 mm for mean annual rainfall and 50-100 mm for seasonal rainfall.

Climate Model Projections

Because simulations using ocean-atmosphere general circulation models (GCMs) are not presently conducted at fine horizontal resolution, the ability to generate climate change scenarios for the small island states is somewhat limited. However, because of the strong influence of the surrounding oceans on the climate of these islands and because the oceans are projected to warm in the future [1-2C for the Caribbean Sea and the Atlantic, Pacific, and Indian Oceans, with a doubling of carbon dioxide (CO2)], small islands also are expected to experience moderate warming in the future. Mean rainfall intensity also is projected to increase by about 20-30% over the tropical oceans (the main locations of the small island states) with doubled CO2. On the other hand, simulations conducted with combined greenhouse gas (GHG) and aerosol forcings project a decrease in mean summer precipitation over the Mediterranean Sea region (the location of Malta and Cyprus).

At this stage, there is much uncertainty in climate model projections with respect to possible changes in the distribution, frequency, and intensity of tropical cyclones and ENSO events. The most significant climate-related projection for small islands is sea-level rise. Current estimates of future global sea-level rise of 5 mm/yr (with a range of 2-9 mm/yr) represent a rate that is 2 to 4 times higher than what has been experienced globally over the past 100 years. Considerable local and regional variations in the rate, magnitude, and direction of sea-level change can be expected as a result of thermal expansion, tectonic movements, and changes in ocean circulation. However, although the level of vulnerability will vary from island to island, it is expected that practically all small island states will be adversely affected by sea-level rise.

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