Combined effects
To calculate the global mean sea level in 2025, scientists averaged data across space and time from Sentinel-6 Michael Freilich, the current official reference satellite for sea level measurements and one of a line of missions developed by NASA and its U.S. and European partners to track the height of about 90% of Earth’s oceans every 10 days.
Then, to better understand the factors that contributed to the rise last year, the researchers looked at measurements from other sources. Among them was the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO), a twin-satellite mission launched by NASA and the German Research Centre for Geosciences that tracks the movement of water (liquid and frozen) by measuring changes in Earth’s gravity over land and ice masses.
The GRACE data indicated that even as ice loss from glaciers and ice sheets continued a long-term trend of water moving from land to oceans, an outsize amount of water moved in the opposite direction in 2025: The heavier-than-normal rainfall due to La Niña shifted water from the oceans to the Amazon basin.
Meanwhile, data from Argo, an international program that uses thousands of seaborne probes to measure ocean temperatures and salinity, showed record warming of the oceans in 2025.
The combined effect of the two factors — one tending to lower sea levels and the other tending to increase them — resulted in an average rise in sea level in 2025 that was less than the average rate based on the long-term data record.
Actionable, accurate, consistent
The continuous series of ocean-observing satellites started with TOPEX/Poseidon, which launched in 1992. Sentinel-6 Michael Freilich, launched in 2020 and took over in 2022 from its predecessor, Jason-3, which is still in orbit and celebrated its 10th launch anniversary on Jan. 17.
In coming months, Sentinel-6 Michael Freilich will pass the baton to its twin, Sentinel-6B, which launched in November. Sentinel-6B is expected to continue ocean measurements for at least five years.
Over more than three decades, the satellites have offered actionable, accurate, and consistent measurements at both local and global scales. These measurements have formed the basis for U.S. flood predictions, which are crucial for safeguarding coastal infrastructure and communities.
The dataset indicates that the average global sea level has gone up by 4 inches (10 centimeters) since 1993. While it’s not uncommon to see short-term ups and downs, the overall trend shows that the rate of annual sea level rise has more than doubled.
“As seas continue to rise globally, satellite monitoring empowers communities worldwide to anticipate risks and build resilience,” said Nadya Shiffer, head of physical oceanography programs at NASA Headquarters in Washington.
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