NASA: La Niña temporarily slowed global sea level rise in 2025, but the long-term trend remains upward
In 2025, the global average sea level rose significantly slower than the year before, despite the fact that oceans simultaneously recorded exceptionally high temperatures. According to NASA's analysis of satellite measurements, the average ocean height rose during 2025 by about 0.03 inches, or 0.08 centimeters. In 2024, the same indicator was about 0.23 inches or 0.59 centimeters, so the difference between the two years is distinct and at first glance suggests a "pause" in the trend. NASA, however, warns that this is not a reversal, but an expected short-term variability associated with the El Niño–Southern Oscillation (ENSO) climate cycle, whose cooler phase, La Niña, can temporarily change the distribution of water between the ocean and land.
A slowdown in sea level rise in a single year does not mean that risks to coasts are decreasing. NASA scientists emphasize that La Niña can temporarily "pull" some water from the ocean onto land through increased precipitation, but this effect is short-lived. Water retained in large river basins, especially the Amazon basin, naturally returns to the oceans through runoff, so as a rule, within less than a year, the sea level growth rate returns to values dictated by ocean warming and the loss of land ice. In other words, the 2025 figure speaks more about the "distribution" of water at a single moment than about a change in the underlying causes of sea level rise.
Why 2025 turned out to be a "slower" year: water temporarily ended up on land
Global sea level rises in the long run due to two fundamental processes: adding water to the oceans by melting land ice (glaciers and the ice sheets of Greenland and Antarctica) and thermal expansion of seawater, which occurs when the ocean warms. NASA's global mean sea level indicator shows that the annual growth rate compared to the beginning of satellite measurements has significantly increased and that the current average growth rate is around 0.17 inches, or approximately 0.44 centimeters per year. However, on top of this "baseline" trend, there are periods of several years in which ENSO can amplify or dampen annual changes through changes in precipitation distribution and water storage on land.
La Niña is the cooler phase of ENSO in the equatorial Pacific. NOAA and NASA state in ENSO explanations that such changes in sea surface temperature in the Pacific can redirect atmospheric circulation and precipitation patterns over large areas. Under La Niña conditions, part of the precipitation belts shifts so that in certain areas, including parts of equatorial South America, heavier rains occur more frequently. When large amounts of rain fall on land, part of the water is temporarily stored in the soil, groundwater, lakes, and rivers, instead of immediately ending up in the oceans. On a global scale, such a shift of water mass from ocean to land can temporarily lower or slow the growth of average sea levels, even while ocean warming and ice melting continue simultaneously.
In NASA's interpretation, this is exactly what happened in 2025: a relatively mild La Niña brought above-average precipitation over the Amazon basin, which temporarily kept a significant portion of water on land. This effect acted as a counterweight to the processes pushing sea levels higher. At the same time, oceans continued to warm, which is important because the ocean's thermal excess directly increases sea levels through expansion, but also indirectly affects extreme weather events and changes in circulation.
NASA researchers: "the cycle is short and faster growth returns quickly"
NASA warns that the temporary influence of La Niña on the global sea level average is part of natural variability that "drives" the numbers up and down, but does not change the direction of the long-term trend. NASA sea level researcher Josh Willis of the Jet Propulsion Laboratory in California said in this context that "weather is taking us on a wild ride," but that such cycles are short-lived. According to his estimate, the excess water that ended up in the Amazon basin usually returns to the oceans in a period of less than a year, after which a return to faster sea level rise is expected.
Therefore, the difference between 2024 and 2025 is not interpreted as opposing the trend, but as an example of how the climatological trend and weather variability overlap in the same measurement. The year 2024 was distinguished by rapid sea level rise, which, according to NASA's analysis, was above expectations and strongly linked to unusual ocean warming. The year 2025 then showed the opposite, but expected "rebound" in which part of the water was retained on land, while the underlying causes of sea level rise remained active. This is why scientists emphasize multi-year trends and acceleration, rather than individual annual jumps or slowdowns.
How global sea level is measured: Sentinel-6 as a reference mission
NASA's calculation of the global average sea level is based on satellite altimetry, or measuring the height of the sea surface from orbit. A central role in today's system is played by Sentinel-6 Michael Freilich, the reference satellite for sea level measurement as part of an international partnership between the US and Europe. Missions in this series track the height of approximately 90% of the world's oceans in an approximately ten-day cycle, providing a consistent global signal through space and time. Such "ocean geodesy" allows changes to be tracked at the millimeter level, which is crucial when global trends are added up over decades.
Continuity of measurement is crucial because only a long series of data allows the separation of short-term oscillations from the climate trend. The satellite array began with the TOPEX/Poseidon mission in 1992, followed by the Jason-1, Jason-2, and Jason-3 missions. Jason-3 was launched on January 17, 2016, and, according to NOAA data, is still active in orbit as part of the ocean monitoring system. Sentinel-6 Michael Freilich was launched in November 2020 and took over the role of reference mission for global sea level in 2022, while Jason-3 remained an important part of the broader measurement and continuity system.
In November 2025, Sentinel-6B was launched, the twin of the Sentinel-6 Michael Freilich mission. The European Space Agency (ESA) and NASA state that Sentinel-6B continues the 30-year series of precise sea level measurements, and it is expected to gradually take over part of the operational burden in the coming months and ensure the continuation of measurements for at least the next five years. In practice, for scientists and coastal planners, this means a more stable and secure flow of data, without "gaps" that would make it difficult to detect acceleration and regional differences.
"Global sea level budget": collision of two processes in 2025
To explain why 2025 turned out to be above-average "quiet" in terms of rise, NASA scientists compare satellite altimetry with independent measurements that help break down the change into causes. This approach is often described as an attempt to close the "global sea level budget," i.e., checking whether the change in sea level can be explained by the sum of contributions from thermal expansion and changes in ocean water mass. In this analysis, the following data sources are particularly important:
- GRACE-FO, a satellite mission that tracks the movement of water mass by measuring changes in Earth's gravity over land and ice areas, which can track ice loss, but also changes in land water storage.
- Argo, an international system of thousands of autonomous floats that measure ocean temperature and salinity and provide the basis for estimating how much the sea expands due to warming.
GRACE-FO data, according to NASA, continue to confirm the long-term direction: melting glaciers and ice sheets transfer water from land to the oceans. However, in 2025, an unusually strong shift in the opposite direction occurred – increased precipitation associated with La Niña retained a significant amount of water in the Amazon basin, which is seen as a temporary "outflow" of water from the ocean to land. At the same time, Argo measurements record a very warm year for the oceans. Specialized climate analyses summarizing multiple datasets state that 2025 was among the warmest years in the instrumental record and that ocean heat content reached record levels, which is important because a warmer ocean directly increases sea levels through thermal expansion.
The combination of these two processes produced a seemingly paradoxical outcome: record warming "pushed" the sea level up through thermal expansion, but the temporary retention of water on land acted as a counterweight. The result was a rise in 2025 smaller than long-term expectations, and even smaller compared to the exceptionally fast year of 2024. In such years, NASA emphasizes that the long-term trend should not be assessed based on a single point, but through multi-year averages and the trend of acceleration.
What the difference between 2024 and 2025 means – and why numbers from a single year can be misleading
NASA warned in its 2024 analysis that global sea levels rose faster than expected, with a significant part of the rise being a consequence of thermal expansion, i.e., unusual ocean warming. The difference between 2024 and 2025 is therefore a good example of how the "climate signal" (long-term warming and ice melting) and "weather noise" (short-term oscillations like ENSO) overlap in the same measurement. A single year can show a smaller increase even when the foundations of the trend are very strong, if temporary storage of water on land or a change in the seasonal cycle of water circulation between ocean and land occurs in the same period.
For coastal protection planning, however, information on acceleration is crucial. NASA's global mean sea level indicator shows that the total rise since 1993 is about 10 centimeters, and that the annual growth rate has increased compared to the beginning of the satellite series. Behind this lies the fact that oceans are warming and land ice is losing mass. Such a trend increases the basic "starting" sea level, so the same weather events – storm, high wave, low pressure, tide – on average more frequently cross the thresholds that cause flooding. This is why sea level rise is increasingly treated in public policies as a risk multiplier, rather than an isolated figure in an annual report.
Consequences on the ground: from flooding to more expensive coastal infrastructure maintenance
Although the global average is expressed in millimeters and centimeters, the consequences are felt locally and often much more strongly. The sea level along the coast depends on currents, temperature, salinity, winds, and water mass distribution, but also on whether the land is rising or sinking. Because of this, the same global rise in one region may only mean more frequent tidal flooding, while in another it can amplify erosion, threaten coastal roads, and increase the risk of sea penetration into sewer and drainage systems. NASA emphasizes that satellite measurements serve not only for scientific monitoring but also for operational needs, including risk assessments and flood forecasts, which are important for the protection of coastal communities and infrastructure.
The European Environment Agency additionally warns that the accelerated sea level rise in European seas is dominantly a consequence of anthropogenic warming. In an analysis of causes, the EEA states that thermal expansion played a larger role in earlier decades, while glacier melting and the loss of mass from Greenland and Antarctica became increasingly significant after 2000. This is important for public policies because it implies that the trend can continue and accelerate even if a single year temporarily deviates, as was the case in 2025 with the La Niña effect. In practice, this means that the issue of coastal protection will increasingly be linked to long-term planning, infrastructure investments, and spatial adaptation.
The broader picture in Europe and the Adriatic: global trend, local specificities
For countries on the Mediterranean, including Croatia, sea level rise is not a theoretical topic, but a practical challenge in spatial planning, tourism, and infrastructure protection. In the Adriatic, the sea level changes due to tides, meteorological influences, and long-term climate fluctuations, and changes can be particularly pronounced in episodes of a combination of wind and low air pressure. The Croatian Hydrographic Institute, in its informative materials on tides, points out that an explicit sea level rise has been observed in the Adriatic in the last decade and explains how global processes – ocean warming and ice melting – create long-term pressure toward higher levels. In local conditions, this trend then "refracts" through the specificities of the Adriatic, from the geometry of the basin to regional meteorological patterns.
The Mediterranean is additionally specific due to the population density of the coastal zone, a large concentration of infrastructure and sensitive ecosystems, as well as the fact that in some areas, soil subsidence processes are recorded. This means that the relative sea level – the one people experience on the coast – can change faster than the global average. In such conditions, the trend of global sea level rise increases the frequency of situations in which the sea overflows onto the shore, and in the long term affects decisions on construction, port renovation, waterfront arrangement, and protection of low-lying coastal zones. Experts warn that adaptation is not a one-time measure, but a process that will have to be aligned with new data and projections, especially as the acceleration signal becomes more clearly manifested in regional trends.
What follows: a new generation of measurements and an increasingly clear acceleration signal
In the scientific community, 2025 is therefore not interpreted as a "year without growth," but as a textbook example of how sensitive the system is to changes in the circulation of water between the ocean and land. Sentinel-6B, which has already started sending data, should further strengthen the continuity of measurements until the end of the decade. Along with altimetry, the combination of data from gravity missions like GRACE-FO and networks of in situ measurements like Argo will remain key, as only in this way can it be reliably separated how much of the sea level change comes from ice melting, how much from thermal expansion, and how much from temporary water shifts over land. This distribution is important not only for science but also for public policies, as it directly says which processes dominate and how they can be expected to change in the future.
Behind these oscillations remains a long-term message that is increasingly clear in NASA's indicators: as oceans warm and as land ice melts, global sea levels continue to rise, and the growth rate through the decades is increasing. La Niña may briefly slow the figure in an annual report, but it cannot change the physics of the system or cancel a trend that has been building for decades. That is why scientists insist on multi-decade series and on reading individual years in context – like waves on the surface, while the average ocean level, driven by the warming of the planet, gradually, but increasingly faster, rises.
Sources:- NASA – analysis of global sea level rise and the role of ENSO (La Niña) in 2025 (published January 30, 2026; transferred in full) link
- NASA Sea Level Change Portal – global mean sea level indicator and current growth rate link
- NASA.gov – „NASA Analysis Shows Unexpected Amount of Sea Level Rise in 2024” link
- NASA Sea Level Change Portal – explanation of how ENSO (El Niño/La Niña) affects sea level link
- NOAA Climate.gov – overview of La Niña development in the 2024/2025 season link
- NOAA NESDIS – Jason-3 mission (mission data and application in sea level monitoring) link
- ESA – Sentinel-6B: first measurement and confirmation of launch in November 2025 link
- NASA Earthdata – Sentinel-6B continues 30-year legacy of sea level measurements link
- NASA JPL – GRACE-FO (monitoring water movement and mass) link
- NASA Sea Level Change Portal – overview of methods (GRACE/GRACE-FO and Argo) in explaining global sea level changes link
- European Environment Agency – global and European sea level rise (causes and trends) link
- Croatian Hydrographic Institute – „Tides and Adriatic sea level” (explanations and context) link
- Carbon Brief – state of the climate in 2025 and ocean heat (summary of multiple datasets) link
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