The scope of this section includes the US-affiliated islands of the Caribbean and Pacific. In the Caribbean, this includes Puerto Rico and the US Virgin Islands. In the Pacific, it includes the Hawaiian Islands, American Samoa, the Commonwealth of the Northern Mariana Islands, Guam, the Federated States of Micronesia, the Republic of the Marshall Islands, and the Republic of Palau.

The Caribbean and Pacific islands that are affiliated with the US provide a unique setting for consideration of climate variability and change. Islands contain diverse and productive ecosystems, and include many specialized and unique species. After centuries of depending on subsistence agriculture and fishing, island economies are now based heavily on tourism, tuna processing and transshipment, and agricultural production for export (including sugar cane, bananas, pineapple, spices, and citrus fruits), making them highly responsive to external economic forces. The stability of these economies is also dependent on the health of the unique natural resources, all of which are sensitive to climate.

Many islands are facing the stresses of rapid human population growth, increasing vulnerability to natural disasters, and degradation of natural resources. Droughts and floods are among the climate extremes of most concern as they affect the amount and quality of water supplies in island communities and thus can have significant health consequences. Due to their small size and isolation, many islands face chronic water shortages and problems with waste disposal. Some are facing a species extinction crisis; for example, the Hawaiian Islands have the highest extinction rate of any state in the nation. For most island communities, infrastructure and economic activities are located near the coast, making them highly vulnerable to storm events and sea-level fluctuations.

Observed Climate Trends

In the Pacific, tropical storms and typhoons are common between May and December, but can occur in any month. In the Caribbean, the hurricane season spans the months from June to November. The El Niño Southern Oscillation (ENSO) cycle affects sea level, rainfall, and cyclone activity (hurricanes or typhoons, depending on the region). In the Caribbean, Atlantic hurricanes are suppressed during El Niño, while they increase during La Niña. In the Pacific, during El Niño events, Hawaii, Micronesia, and the islands of the southwest tropical Pacific often receive below normal rainfall. Additionally, areas of above normal precipitation, along with greater tropical cyclone activity, typically shift eastward towards French Polynesia. The region of greater tropical cyclone activity includes the central Pacific (Hawaiian waters), eastern Marshalls and Guam, and northern Marianas.

Over the last century, average annual temperatures in the Caribbean islands have increased by more than 1F (0.5C). Average annual temperatures in the Pacific Islands have increased by about 0.5F (0.25C). Globally, sea level has risen by 4 to 8 inches (10-20 cm) in the past 100 years with significant local variation. Relative sea level, which also takes into account natural and human-caused changes in the land elevation such as tectonic uplifting and land subsidence (sinking), is also showing an upward trend (3.9 inches, about 10 cm, per 100 years) at sites monitored in the Caribbean and Gulf of Mexico. Although absolute sea level is also rising in the Pacific, trends vary greatly from island to island due to the fact that some islands are rising; ENSO and other short-term variations further complicate the picture. Low-lying islands that are not rising are very likely to be at risk from sea-level rise.

Scenarios of Future Climate

Pacific and Caribbean islands will possibly be affected by: changes in patterns of natural climate variability (such as ENSO); changes in the frequency, intensity, and tracks of tropical cyclones; and changes in ocean currents. These islands are very likely to experience increasing air and ocean temperatures and changes in sea level (including storm surges and sustained rise). Some recent climate model studies also project that ENSO extremes are likely to increase with increasing greenhouse gas concentrations. Some models suggest more persistent El Niño-like conditions across the Pacific. This would lead to a reduction of fresh water resources in areas of the western Pacific, Micronesia, and the southwest tropical Pacific, and a reduction in Atlantic hurricane frequency.

One hurricane modeling study suggests that peak wind speed will increase by 5-10% by the end of the 21st century along with significant increases in peak precipitation rates. Apart from the linkage with ENSO, there is significant uncertainty about how increasing global temperatures will affect hurricane and typhoon frequency and tracks.

Freshwater Resources

Adequate water supplies are critical for the well-being and economic security of the islands and are needed for tourism, agriculture, fish processing, and urban/municipal users, as well as natural ecosystems. On many islands, water resources or access to them are already limited and subject to competing demands. It is possible that climate change and the resulting sea-level rise will adversely affect water supplies in the future through more frequent droughts, floods, and salt water intrusion into freshwater lenses. The populations of the Pacific Islands are primarily concerned with future conditions that are likely to exacerbate drought. In Puerto Rico and the US Virgin Islands drought is also a concern, as are flooding and landslides associated with heavy precipitation events.

Adaptations: Strategies for providing adequate water resources include improved rainfall catchment; improved storage and distribution systems; development of under-utilized or alternative sources, better management of water supply and infrastructure; increased water conservation programs; construction of groundwater recharge basins for runoff; more effective use of ENSO forecast information; and application of new technology, such as desalinization. For agriculture, strategies include exploring the feasibility of planting more drought-resistant crops. Consideration of the effects of climate change and variability on freshwater resources should be integrated into community planning and tourism development.

Public Health and Safety

Both coastal and inland island populations and infrastructure are already at risk from climate extremes. Storms can damage or destroy buildings, damage infrastructure, and disrupt public services. Both the Pacific and Caribbean regions are familiar with severe cyclones, which have caused billions of dollars in damage from the destruction of housing, agriculture, roads and bridges, and lost tourism revenue. In both regions, a large percentage of people, infrastructure, and economic activities are located near the coast, leading to dense areas of vulnerability. The unique topography of Puerto Rico and the Virgin Islands makes them susceptible to floods and landslides often resulting from severe storms. It is possible that the frequency of extreme events may increase over the next few decades to a century thereby increasing the risk to public health and safety.

Adaptations: Strategies include upgrading and protection of infrastructure, comprehensive disaster management programs, changes in land use policies, and adoption and enforcement of more stringent building codes. For reducing public health risks, strategies include improved sanitation and health care infrastructure, emergency plans, and public education about health risks posed by floods and droughts.

Ecosystems and Biodiversity

resources are already threatened by invasive non-native plant and animal species, as well as urban expansion and various industrial activities, resulting in the highest extinction rates of all regions of the US. They can also be highly climate-sensitive. For example, coral bleaching associated with El Niño events and the long-term warming of surface waters has become widespread in both the Pacific and Caribbean since the 1990s. During the El Niño of 1997-98, coral bleaching in Palau, known for its spectacular coral reefs, was extensive.

Other possible concerns include increased extinction rates of mountain species that have limited opportunities for migration; increased rates of changes in mangrove ranges and health; and declines in forests due to floods, droughts, or increased incidence of pests, pathogens, or fire. It is

possible that increases in the frequency or intensity of hurricanes would generally favor invasive species. In addition, the unique cloud forests -- located on some of the islands occupy a narrow geographical and climatological niche. A slight shift in temperature or precipitation patterns would possibly cause this zone to shift upwards enough to be eliminated.

Adaptations: While options are limited, strategies include efforts at slowing biological invasions, strengthening and enforcing policies that protect critical habitats, improving understanding of the local effects of climate variability and change, and increasing the awareness of tourists and the public concerning the value of species and biodiversity.

Sea-Level Variability

Sea-level rise, both long-term and episodic, is already an extremely important issue for many of the islands. Sea-level rise results in coastal erosion. inundation, and salt water intrusion into freshwater lenses and coastal agricultural zones (where taro, pulaka, and yams are grown). Future sea-level rise, both global and due to episodic events (such as extreme lunar tides, ENSO-related changes, and storm-related wave conditions) will increasingly contribute to negative consequences for island populations and ecosystems. Most at risk are low-lying islands and atolls. Examples of sites that are already close to sea level include the Republic of the Marshall Islands in the Pacific and much of the metropolitan area of San Juan in Puerto Rico.

Adaptations: Strategies include efforts to protect coastal infrastructure, transportation and water systems, agriculture, and communities; integrated coastal zone management; and crop diversification and the use of salt-resistant crops. Retreat from risk prone areas is likely to be necessary in some cases, but will be complicated due to land ownership, and could have significant consequences for social and cultural identity.