A NASA analysis showed a surprising rise in sea levels in 2024. Last year’s rise was driven by unusually strong ocean warming combined with the melting of land ice such as glaciers. As a result, Hawaii, for example, is sinking 40 times faster than scientists had previously thought, with some parts of the island chain sinking at a rate of 0.6 millimeters per year, but others are in much worse shape.
Global sea levels rose faster than expected in 2024, largely because ocean water expands as it warms, or thermally expands. The rate of rise last year was 0.23 inches (0.59 centimeters) per year, compared with an expected 0.17 inches (0.43 centimeters) per year, according to an analysis by NASA.
Coastal communities like Florida, shown in this 1992 NASA image, are vulnerable to the impacts of rising seas, including flooding during high tides. A new analysis by the agency found a higher-than-expected rate of sea level rise in 2024, which also happens to be the hottest year on record. NASA
“The rise we saw in 2024 was higher than we expected,” said Josh Willis, a sea level researcher at NASA’s Jet Propulsion Laboratory in Southern California. “Every year is a little different, but it’s clear that the ocean is continuing to rise, and the rate of rise is getting faster and faster.”
In recent years, about two-thirds of sea level rise has come from water flowing from land into the ocean as ice sheets and glaciers melt. About a third has come from thermal expansion of seawater. But in 2024, these contributions have reversed, with two-thirds of sea level rise coming from thermal expansion.
“As 2024 became the warmest year on record, Earth’s expanding oceans are following suit, reaching their highest levels in three decades,” said Nadia Vinogradova-Schiffer, program manager for physical oceanography and the Integrated Earth Observatory at NASA Headquarters in Washington.
Since satellite observations of sea levels began in 1993, the rate of annual sea level rise has more than doubled. In total, sea levels worldwide have risen 4 inches (10 centimeters) since 1993.
This graph shows global average sea level (in blue) since 1993, measured by a series of five satellites. The solid red line shows the trajectory of this rise, which has more than doubled over the past three decades. The dashed red line projects future sea level rise. NASA/JPL-Caltech
This long-term record was made possible by a continuous series of ocean-observing satellites, beginning with TOPEX/Poseidon in 1992. The current ocean-observing satellite in this series, Sentinel-6 Michael Freilich, was launched in 2020 and is one of an identical pair of spacecraft that will carry this sea-level dataset into its fourth decade. Its twin, the upcoming Sentinel-6B satellite, will continue to measure sea-surface heights down to a few centimeters for about 90% of the world’s oceans.
There are several ways that heat enters the ocean, causing the water to expand thermally. Generally, seawater is arranged in layers determined by the temperature and density of the water. Warmer water floats on the surface and is lighter than colder water, which is denser. In most places, heat from the surface moves very slowly through these layers down into the depths of the ocean.
But extremely windy areas of the ocean can shake the layers hard enough to cause vertical mixing. Very strong currents, such as those in the Southern Ocean, can tilt the ocean layers, allowing surface water to more easily slide down into the deep.
The massive movement of water during El Niño, when a large volume of warm water normally found in the western Pacific Ocean spills into the central and eastern Pacific Ocean, can also lead to vertical movement of heat in the ocean.
Hawaii is sinking 40 times faster than scientists thought. Some parts of the island chain are sinking at a rate of 0.6 millimetres a year, but others are in much worse shape.
Because islands like Oahu drift very slowly away from the magmatic hotspot that once formed them, the island’s weight gradually causes it to sink into the ocean at a rate of about 0.6 millimeters per year.
But new research shows that in some areas of Oahu, subsidence rates could be as high as 25 millimeters per year, about 40 times faster than expected.
Researchers believe this is largely because some areas, like the more industrial Mapunapuna region, are subject to compaction because they were originally built on sediment and man-made fill.
Hawaii’s geological history has historically been one of ascent. More than a million years ago, when the Pacific island plate moved atop a volcanic spur rising through the Earth’s crust, volcanic islands at sea level formed what would eventually become the 50th U.S. state. Now, new research from the University of Hawaii at Manoa reports that the island chain may be changing course — literally.
Hawaii is sinking underwater. mir24.tv
Published in the journal Communications Earth & Environment, the study analyzed subsidence (the gradual collapse or sinking of an area) on the island of Oahu, home to Pearl Harbor and the state capital of Honolulu. They found that in some areas of the island, located 185 miles northwest of the Big Island (or Hawaii), which sits atop an island chain hotspot, the rate of subsidence was only about 0.6 millimeters per year. However, they also documented areas that were sinking a staggering 40 times faster — about 25 millimeters per year. That rate, along with the localized nature of the subsidence, raised a few eyebrows among the researchers.
“Our results show that land subsidence is an important but often overlooked factor when assessing future flood impacts,” Kyle Murray of UH Manoa, lead author of the study, said in a press release. “In rapidly subsiding areas, the effects of sea level rise will be felt much sooner than previously thought, meaning we must prepare for flooding on a more immediate timeline.”
One reason for this discrepancy is that industrial areas like Mapunapuna are built on sediment and artificial fill, which researchers say results in more compaction than other areas of Oahu. This rate of subsidence far outpaces the long-term rate of sea level rise, which is about 1.54 millimeters, and could cause problems for the region’s shorelines in the near future.
“In places like the Mapunapuna industrial region, land subsidence could increase floodplain area by more than 50 percent by 2050, while reducing flood preparedness by up to 50 years,” Phil Thompson of UH Manoa, a co-author of the study, said in a press release.
Climate-focused efforts on Oahu, like the science-based, community-driven Climate Ready O’ahu program, are preparing for rising sea levels and increased soil erosion, as well as other climate-driven events like wildfires and flash floods. While preserving wetlands and dune ecosystems will help stabilize shorelines, researchers note that accounting for these alarming rates of subsidence will be vital to understanding the true timeframe needed to implement these climate adaptation strategies.
“Our research provides critical data that can be used to inform decision making at the state and county levels, helping to improve flood vulnerability assessments, infrastructure resilience, and long-term urban planning,” said UH Manoa’s Chip Fletcher, co-author and director of the Climate Resilience Collaborative, in a press release. “This work directly serves Hawaii residents by ensuring that local adaptation strategies are based on the best available science.”
