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Climate Change

U.S. Tropical Islands

Climate Impacts in the U.S. Islands

Map of the Hawaii and Puerto Rico islands.
Key Points
  • Sea level rise could threaten the water supplies, ecosystems, and infrastructure of U.S. tropical islands.
  • Warmer and more acidic oceans would stress coral reefs, which have already been harmed by pollution.
  • Climate change could have significant economic impacts on island tourism and fisheries.
Line graph that shows annaul precipitation decline in the Caribbean. Simulations for 1900 to 2000 show a slight decline of three or four percent over the decade. Under a lower emissions scenario precipitation is projected to decrease by about six percent. Under the higher emissions scenario, precipitation is projected to decrease by about twenty percent by the end of the 21st century. View enlarged image

Caribbean Precipitation Change (1900 to 2100): Total annual precipitation has declined in the Caribbean and climate models project stronger declines in the future, particularly under higher emission scenarios. Such decreases threaten island communities that rely on rainfall for replenishing their freshwater supplies. The shaded areas show the likely ranges while the lines show the central projections from a set of climate models. Source: USGCRP (2009)

The U.S. tropical islands include Puerto Rico and the U.S. Virgin Islands in the Caribbean and Hawaii, Guam, the Northern Marianas Islands, and American Samoa in the Pacific. Each island has its own climate, geology, topography, industries, and culture, but some impacts of climate change could bring similar challenges to all island communities.

Many climate change impacts are likely to affect island communities in both the Caribbean and Pacific, including higher sea levels, more powerful tropical storms (such as hurricanes in the Atlantic and typhoons in the Pacific), and warmer, more acidic coastal waters. Unique island ecosystems, such as coral reefs and mangrove forests, are already facing stress from human development and pollution, making them particularly sensitive to additional stresses from climate change. [1] Buildings and important infrastructure on the coast could also be particularly sensitive to climate change impacts. [1]

Islands in both the Caribbean and the Pacific are likely to experience significant warming in the next century. Projections for warming by 2100 range from approximately 2.5°F to over 6°F, depending on global greenhouse gas emissions throughout the 21st century. [1] In the Caribbean, precipitation is projected to decrease overall. In the Pacific, summer precipitation and the frequency of heavy downpours is projected to increase. [1] Rising sea levels are likely to increase the frequency and severity of floods during storms, as well as to erode and inundate coastlines.

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Impacts on Water Resources

Climate change will likely affect the availability of water on some islands, particularly on small islands and atolls. Ground and surface waters on many small islands are recharged by rainfall. Some islands are projected to experience decreases in precipitation, while others may see increases. [1]

Drawing of a coastal parcel of land that has a house with a well that extends down into the freshwater lens. The image shows rainfall, the ocean, and land with a subterranean sketch. The land below the ocean is labeled as seawater and low permeability sediments. A region labeled freshwater lens is located below the land that is above the ocean level. Another region labeled infiltration lies at the ocean level below the land of the island (or other coastal land represented by the drawing). View enlarged image

Freshwater Lens: Many island communities depend on freshwater lenses, pictured here, which are recharged by precipitation. The amount of water contained by a freshwater lens is determined by the size of the island, the amount of rainfall, rates of water withdrawal, the permeability of the rock beneath the island, and salt mixing due to storm- or tide-induced pressure. Freshwater lenses can be as shallow as 4 to 8 inches or as deep as 65 feet. Source: USGCRP (2009)

In the Caribbean, where rainfall is projected to decrease, water supplies are likely to be reduced. Sea level rise and coastal erosion can also reduce water availability by inundating land with saltwater, contaminating freshwater and preventing recharge of the freshwater supply. On islands where populations are growing, or where infrastructure is old or poorly maintained, the impacts on water supplies may be especially severe. [1]

Though increases in precipitation may help ensure a supply of freshwater, heavy rainfall events could lead to flooding and landslides, which can reduce water quality and cause damage. In addition, the water infrastructure systems of some islands could be overloaded during heavy rainfall, affecting their ability to distribute drinking water or safely process wastewater. [1]

In the Pacific Islands, heavy rainfall is projected to increase, which may lead to more frequent flooding that could compromise the quality of water supplies and affect crop yields. [1] As explained in the Water Resources and Health pages, flooding events can cause sewage or agricultural pollution to flow into water supplies, which can present risks to human health.

For more information about climate change impacts on water, please visit the Water Resources page.

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Impacts on Ecosystems

Islands are home to unique ecosystems and species that provide economic opportunities, safety, nourishment, and cultural value to island communities. [1] [2] Changes in sea level, temperature, and the acidity of coastal waters could threaten the stability and functioning of these ecosystems.

Photograph of rocky beach in a cove with bright blue water.

Example of Pacific island habitat. Source: USGCRP (2012)

For example, coral reefs represent an important habitat for many fish and marine animals. They also provide shoreline protection, valuable fisheries, and revenue through tourism. In Hawaii, reefs are estimated to bring in $360 million each year, and are valued at more than $10 billion. In the Caribbean, coral reefs provide annual benefits of more than $3 billion. [1] Reefs already face serious threats from water pollution. Warmer, more acidic coastal waters would likely serve as a further stress on many reefs.

The loss and inundation of other coastal habitats, such as mangroves, from sea level rise and storm surge could endanger species that use these habitats for nesting, nursing, and nutrients. [1]

Additionally, climate change may enhance conditions that facilitate the spread of invasive species and marine and terrestrial pathogens and diseases, which would affect an island's natural ecosystems and biodiversity. [2]

For more information about climate change impacts on coasts, please visit the Coastal Impacts page.

For more information about climate change impacts on ecosystems, please visit the Ecosystems Impacts page.

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Impacts on Agriculture and Food

Many island populations depend on local crops and fisheries for their survival and economic development.

In the Pacific, almost all communities derive more than 25% of their animal protein from fish. [1] Changes in ocean temperatures could cause migratory shifts in fish species and damage to fish habitats. These impacts would exacerbate existing stresses on the fisheries, such as those from pollution and overfishing, and ultimately may lead to a decline in the abundance and health of fishery populations. [2]

Changes in climate are also likely to hurt coastal agriculture. In particular, sea level rise may lead to inundation or cause soils to become saltier and less fertile on some islands. Water supplies can suffer as a result of reductions in rainfall or from salt water intrusion. [2]

For more information about climate change impacts on agriculture and food, please visit the Agriculture and Food Impacts page.

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Impacts on Infrastructure, Economy, and Culture

Aerial photograph of islands with lots of trees and some houses.

Coastal houses and an airport in the U.S.-affiliated Federated States of Micronesia rely on mangroves' protection from erosion and damage due to rising sea level, waves, storm surges, and wind. Source: USGCRP (2009) (PDF)

Climate change could have far-reaching effects on island infrastructure, economic development, and local culture. Island settlements, social and leisure events, and economic activity tend to be concentrated close to the coast, making them vulnerable to climate change impacts from coastal inundation, flooding, and shoreline erosion. [1] [2]

Inundation, flooding, and shoreline erosion could affect critical infrastructure, such as airports, roads, ports, and hospitals. As the frequency and intensity of strong storms and flooding is projected to increase, infrastructure may need to recover faster and become more resilient to these impacts. Long-term infrastructure damage could disrupt services, including disaster risk management, health care, education, natural resource management, and economic activity in sectors such as tourism and trade. [1] [2]

Climate change impacts will likely affect tourist activities. Sea level rise, warming water temperatures, increasing storm intensities, beach erosion, and ocean acidification could pose risks to beaches and threaten coastal activities, such as coral reef exploration, boating, and fishing. Tourism is a major economic activity for islands. In Puerto Rico, 3.5 million tourists spent $3.5 billion in 2009. [3] In Hawaii, tourism brought 7 million visitors to the islands in 2006 and generated more than $12 billion for the state. In the Caribbean, coral reefs provide annual net benefits from fisheries, tourism, and shoreline protection services of between $3.1 billion and $4.6 billion (in 2006). [1] [2]

For more information about climate change impacts on culture, please visit the Society page.

To learn more about what the U.S. tropical islands are doing to adapt to climate change impacts, please visit the adaptation section of the U.S. Islands Impacts and Adaptation page.

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[1] USGCRP (2009). Global Climate Change Impacts in the United States . Karl, T. R., J. M. Melillo, and T. C. Peterson (eds.). United States Global Change Research Program. Cambridge University Press, New York, NY, USA.

[2] Mimura, N., L. Nurse, R.F. McLean, J. Agard, L. Briguglio, P. Lefale, R. Payet and G. Sem (2007). Small Islands. In: Climate Change 2007: Impacts, Adaptation and Vulnerability . Exit EPA Disclaimer Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change Parry, M.L., O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E. Hanson, (eds.). Cambridge University Press, Cambridge, United Kingdom.

[3] UNWTO (2011). UNWTO Tourism Highlights: 2011 Edition (PDF). Exit EPA Disclaimer United Nations World Tourism Organization.

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