The question of whether the Hawaiian Islands will eventually be submerged by rising ocean waters reflects a deep concern for the future of this unique archipelago. The high volcanic peaks and steep slopes of the islands are not at risk of vanishing entirely. However, focusing on the islands’ elevation ignores the immediate and accelerating threat to the low-lying coastal plains where nearly all of Hawaii’s population, infrastructure, and cultural sites are concentrated.
This threat comes from sea level rise (SLR), the increase in the average height of the ocean relative to land over time. Understanding the future of Hawaii requires examining the precise scientific projections, both global and local, that determine the vulnerability of these coastlines. The scientific consensus indicates that while the islands will remain, the habitability and economic viability of the shorelines face a profound transformation.
Global Drivers and Projections for Sea Level Rise
The primary forces driving the global rise in sea level originate from two physical processes linked to the planet’s warming climate. The first is the thermal expansion of ocean water, where the sea expands as it absorbs excess heat. The second, and increasingly dominant, factor is the addition of water volume from the melting of land-based ice, specifically glaciers and continental ice sheets in Greenland and Antarctica.
This mechanism has already caused the global mean sea level (GMSL) to rise by approximately 8 to 9 inches since 1880, and the rate is accelerating. Between 2006 and 2018, the average rate of GMSL increase reached about 3.7 millimeters per year, nearly double the rate observed during the 20th century. Under current high greenhouse gas emission pathways, the Intergovernmental Panel on Climate Change (IPCC) projects a GMSL rise of between 0.63 and 1.01 meters (roughly 2 to 3.3 feet) by 2100.
These projections represent the “likely range” for the global average, but higher outcomes remain possible. Scenarios that include the rapid collapse of parts of the Antarctic ice sheet, though less probable, could potentially lead to a global rise of up to 2 meters (6.6 feet) by the end of the century.
The global figures serve as a baseline but cannot accurately predict the local reality for a specific coastline like Hawaii’s. Ocean dynamics and geological processes ensure that sea level rise is not experienced uniformly across the planet. Therefore, understanding Hawaii’s situation requires applying these global drivers to the unique physical conditions of the mid-Pacific.
Localized Factors Shaping Hawaii’s Vulnerability
Global sea level projections are insufficient for Hawaii because localized factors significantly amplify the final rate of rise felt at the shore. Studies indicate that the ocean around the Hawaiian Islands is projected to experience a sea level rise 16% to 20% higher than the global average for the tropical Pacific. This regional magnification is due to shifts in ocean currents, changes in heat distribution, and the gravitational effects of distant ice sheet melt.
Another factor is the movement of the land itself, known as vertical land motion, which determines the relative sea level rise (RSLR). The islands are generally subsiding slowly as they move away from the volcanic hotspot that created them. However, in certain urban areas, the sinking rate is dramatically increased by human activity.
Localized subsidence on the south shore of Oʻahu, for example, is occurring nearly 40 times faster than the island’s natural sinking rate. This rapid localized movement, which can exceed 25 millimeters per year, is often attributed to the compaction of artificial fill and sediment upon which coastal infrastructure was built. This geological reality means the effects of rising sea levels are being felt sooner than anticipated in those specific areas.
This acceleration is already evident in tide gauge measurements, which show that the local sea level around the islands has risen by 5 inches since 1970. Based on these local factors, intermediate projections for Hawaii anticipate a rise of 8 inches by 2050. The intermediate-high scenario, often used for planning public infrastructure, suggests a sea level rise of nearly 6 feet by 2100.
Current Impacts: Infrastructure Loss and Groundwater Salinization
The consequences of rising relative sea level are an immediate reality for coastal Hawaii. One visible effect is the sharp increase in high-tide, or “nuisance,” flooding. The frequency of these minor coastal flooding events has already increased from about two days per year in the 1970s to 40 days per year in the 2010s.
This flooding routinely affects low-lying areas like Waikīkī and causes disruptions, such as road closures, that impact daily life and the state’s economy. Projections indicate this trend will worsen, with some areas expecting up to 150 high-tide flood days per year by 2050. As the ocean level increases, the threshold for flooding is crossed more often, meaning minor events become chronic.
The rising ocean is also creating a threat beneath the surface through groundwater salinization. Sea level rise pushes the freshwater lens, which floats atop denser saltwater, upward and landward. This causes the coastal water table to rise and become saltier. This elevated saltwater then interacts with buried infrastructure, including sewer lines, drainage systems, and building foundations, causing deterioration decades before any surface flooding is observed.
The threat to public works is substantial, as much of the state’s infrastructure is located on these vulnerable coastal plains. In Oʻahu, over $12.9 billion worth of infrastructure is at risk from the combined effects of rising sea levels and land subsidence. Assets like airports, major roads, and military infrastructure around Pearl Harbor face growing vulnerability to inundation and structural damage.
The acceleration of coastal erosion is the most widely observed impact, directly threatening the state’s natural barriers and tourism economy. Sea level rise increases the intensity of coastal erosion, leading to the potential loss of up to 40% of Hawaii’s beaches by 2050. Research shows that the rate of shoreline retreat may double by mid-century, with some beaches facing an additional 16 to 20 feet of landward movement. This loss of sandy beaches eliminates natural storm protection and threatens thousands of homes and cultural sites built near the shoreline.
Assessing the Long-Term Fate of Hawaiian Coastlines
The long-term outlook confirms that the islands are not disappearing, but widespread, permanent inundation of their most developed areas is certain. The severity of the threat is localized, not existential for the entire archipelago. Scientists project that chronic flooding will render approximately 25,800 acres of coastal land unusable.
While this represents only about 0.5% of the state’s total land area, it is the most densely populated and economically significant zone. This permanent loss is projected to impact:
- 6,500 structures.
- 550 cultural sites.
- 38 miles of major highways.
The ultimate fate of these coastlines hinges on which emission pathway the world follows, with worst-case scenarios for Hawaii suggesting a total sea level rise of up to 8 feet by the end of the century.
Public infrastructure planning now incorporates a projected 6 feet of sea level rise to ensure new construction can withstand the predicted conditions. This planning acknowledges that the ocean will permanently claim much of the low-lying land where development has occurred, forcing communities to adapt by either hardening shorelines or retreating entirely. The core landmass of the Hawaiian Islands will endure, but the coastlines that define the modern state face an irreversible transformation.