Image credit : https://science.feedback.org/
Global mean sea level is rising, and the rate of that rise has increased over the past six decades. Tide gauges, satellite altimeters, ocean floats, and ice-mass measurements now close the sea-level budget to within a few tenths of a millimeter per year. The picture they paint is consistent: the ocean is expanding as it absorbs heat, land ice is adding water, and both processes have sped up as the planet has warmed.
Since 1901, global mean sea level has risen by roughly 20–23 cm. The average rate over much of the twentieth century was about 1.4–1.7 mm per year. That pace was already faster than in preceding centuries. After the 1960s the rate increased; during the satellite era that began in 1993 it averaged about 3.3–3.6 mm per year. Instantaneous rates have roughly doubled within that record, from around 2.1 mm per year in the early 1990s to about 4.5 mm per year by the end of 2023. Over 2005–2023 the linear rate was 3.94 mm per year. Copernicus Climate Change Service data show a 31 percent increase from 2.92 mm per year in 1999–2009 to 3.82 mm per year in 2015–2025, an acceleration of about 0.8 mm per year per decade. A 2024 analysis of the 31-year altimetry record found an acceleration of 0.08 ± 0.06 mm yr⁻². In other words, it took 12 years to accumulate the first 30 mm of satellite-era rise, nine more years to reach 60 mm, and only 7.5 years to reach 90 mm. Total rise from 1993 through 2023 was about 111 mm.
Year-to-year fluctuations still matter. El Niño years tend to raise global mean sea level because more rain falls over the tropical ocean; La Niña years do the opposite. In 2024 the ocean rose by about 5.9 mm, well above the recent average, largely because of exceptional ocean warming and thermal expansion. In 2025 persistent La Niña limited the rise to only 0.08 cm—below the long-term satellite-era expectation of 0.44 cm per year—even as ocean heat content set another record. Those short-term swings do not erase the underlying acceleration.
U.S. coastal records tell a similar story. A 2025 analysis of 70 long tide-gauge records along the contiguous United States found that the rate more than doubled from about 1.7 mm per year in 1900 to about 4.3 mm per year in 2024, with recent rates above the century-long mean of roughly 3.0 mm per year. That conclusion used the full set of long, active gauges rather than a handful of stations and directly contradicts claims that U.S. tide gauges show no acceleration. Relative sea level at the coast also includes local land motion, so some places experience substantially faster rise than the global mean.
What is driving the acceleration
Two processes dominate: thermal expansion of seawater and the addition of meltwater from land ice. Since 1960, thermosteric expansion has accounted for about 43 percent of the observed trend and 41 percent of the acceleration. Mountain glaciers contributed 27 percent of the trend but only 9 percent of the acceleration. Greenland supplied 15 percent of the trend and 16 percent of the acceleration; Antarctica 12 percent and 13 percent. Changes in terrestrial water storage (groundwater, reservoirs, soil moisture) were a small part of the long-term trend (3 percent) but a larger share of the recent acceleration (21 percent). In the altimetry era the mix shifts somewhat: thermal expansion still leads, followed by glaciers, Greenland, Antarctica, and land water. Budget studies now close to within 0.18 mm per year for 1960–2023 and even more tightly after 2005. The residual between observed sea level and the sum of independently measured contributions is only a few millimeters.
The physical reasons are straightforward. The ocean has absorbed more than 90 percent of the excess heat trapped by greenhouse gases. Warmer water is less dense and occupies more volume. At the same time, mountain glaciers and the Greenland and Antarctic ice sheets have lost mass at increasing rates. Greenland’s contribution grew from a few tenths of a millimeter per year in the 1990s to several times that later. Parts of West Antarctica, including glaciers that rest on bedrock below sea level, have accelerated as warmer ocean water thins the ice shelves that hold them back. Land-water storage has also changed: earlier in the twentieth century large dam construction temporarily held water on land and slowed sea-level rise; later, groundwater pumping and other withdrawals added water to the ocean.
Human influence is the main driver of the observed rise since at least 1971. Natural variability—volcanic eruptions, the El Niño–Southern Oscillation, the Atlantic Multidecadal Oscillation—modulates the rate from year to year and decade to decade, but it does not explain the multi-decadal acceleration. Some analyses identify an abrupt steepening around 2010–2012, possibly linked to a reduction in cooling aerosols as air-quality regulations took effect and to the emergence of deeper ocean warming. Whether the change is best described as a smooth quadratic acceleration or as a step to a higher linear rate, the recent pace is clearly faster than the mid-twentieth-century pace.
Regional differences and local risk
Global mean sea level is an average. Regional rates vary because of ocean circulation, wind patterns, gravitational effects of ice-mass loss, and vertical land motion. The western tropical Pacific has seen rates several times the global mean. Parts of the U.S. East and Gulf coasts experience additional rise from land subsidence caused by sediment compaction, groundwater extraction, and glacial isostatic adjustment. In some deltas—the Nile, Mekong, Yellow River, and others—subsidence can exceed the rate of ocean rise, multiplying the effective local change. Studies that compare tide-gauge observations with geoid models also suggest that the present-day baseline water level is higher in many places than standard global models imply, increasing the number of people already living on land that is, in effect, below mean sea level.
The practical consequence is not only a slowly rising average water line. Higher mean sea level raises the entire distribution of water levels, so historically rare high-water events become more frequent. One attribution study concluded that human-driven sea-level rise has already quadrupled the global frequency of what used to be 1-in-100-year extreme sea-level events since 1900; the median increase in frequency of such events is even larger. Nuisance flooding, saltwater intrusion into aquifers and wetlands, shoreline erosion, and infrastructure damage have already increased in many low-lying cities. Even a few tens of centimeters matter when they coincide with storms, high tides, or heavy rain.
What comes next
Sea level will continue to rise for centuries because of the heat already stored in the ocean and the slow response of ice sheets. How fast and how far depends on future emissions and on ice-sheet processes that remain uncertain. IPCC AR6 likely ranges for 2100, relative to 1995–2014, run from 0.28–0.55 m under a very low emissions pathway to 0.63–1.01 m under a very high pathway. Under high warming, low-confidence ice-sheet instabilities could produce substantially larger rise. If the satellite-era acceleration simply continued, mid-century and late-century rates would reach several millimeters per year higher than today’s, producing another 17 cm or more in the next three decades alone. Recent work on Antarctica suggests that the current rate of ice loss is a useful predictor of the next few decades, which may limit near-term surprises even while longer-term risk remains large.
Adaptation therefore cannot wait for the last decimal place of a 2100 projection. Coastal planning, flood defenses, managed retreat in the most exposed places, and protection of groundwater and wetlands are already required. Mitigation still matters: lower emissions reduce the committed rise after 2100 and shrink the chance of the highest-end ice-sheet outcomes. The observational record is now long enough, and the budget closed tightly enough, that the acceleration itself is no longer in serious scientific dispute. The remaining questions are how much additional ice the great sheets will lose, how uneven the rise will be from coast to coast, and how quickly societies will adjust to a higher, faster-rising ocean.