The Pacific Island region faces a range of challenges associated with sea level rise. Higher water levels threaten coastal structures and property, groundwater reservoirs, coral reef ecosystems, harbor operations, wastewater systems, airports, and other resources of social and economic concern. Low islands are especially vulnerable given their limited elevation above present-day sea level. By the end of this century, projected sea levels are likely to exceed important thresholds: combined with possible climate-related changes in storm patterns and regional winds, rising seas may lead to chronic high water levels along many Pacific Island coasts.
Much coastal damage occurs as a result of elevated water levels. For instance, storm surges related to tropical and extra-tropical storms can cause damaging inundation events. Distant storms can also increase island sea levels through the generation and propagation of breaking ocean waves. Elevated water levels result from of a complex interplay of oceanic, atmospheric, and cryospheric processes. Extreme water levels may be related to changes in global or regional mean sea level, the status of the El Niño-Southern Oscillation (ENSO) and other modes of natural variability, storms that occur nearby or at a distance, unusually high tides, and/or vertical land motion.
Future sea levels
Climate variability patterns—most notably, ENSO—affect regional mean sea level on varying time scales. Although sea level height variations related to these conditions are generally weak, they can influence estimates for sea level trends. After accounting for a wide range of factors, however, projections suggest that over the 21st century, sea level in the Pacific will rise at about the same rate as the projected increase in global average sea level.
On low islands, critical public facilities and infrastructure as well as private commercial and residential property are especially vulnerable. Agricultural activity will also be affected, as sea level rise decreases the land area available for farming and periodic flooding increases the salinity of groundwater. Coastal and nearshore environments will progressively be affected as sea levels rise and high wave events alter low islands’ sizes and shapes.
Impacts to the built environment on low-lying portions of high islands, where nearly all airports are located and where each island’s road network is sited, will be nearly as profound as those experienced on low islands. Islands with more developed built infrastructure will experience more economic impacts from tourism loss. In Hawai‘i, for example, where tourism comprises 26 percent of the state’s economy, damage to tourism infrastructure could have large economic impacts—the loss of Waikīkī Beach alone could lead to an annual loss of $2 billion in visitor expenditures.