Ocean warming causes thermal expansion, and melting glaciers and ice sheets add water from land. Local sea level can rise faster or slower than the global average because land moves and ocean circulation and gravity redistribute water.
Three things to know
- Two main causes
- Expansion + land ice
- Both respond to planetary warming.
- Measured by
- Gauges + satellites
- Tide gauges provide long local records; altimeters map the global ocean.
- Local difference
- Relative sea level
- Communities experience water level relative to moving land.
A warmer ocean occupies more space
Water expands as it warms across most ocean temperatures. Because the ocean is deep and vast, even a small average density change adds measurable volume. Heat is distributed unevenly, creating regional sea-level patterns.
Land ice adds water
Melting mountain glaciers and net loss from the Greenland and Antarctic ice sheets transfer water stored on land into the ocean. Melting floating sea ice has little direct effect on sea level because it already displaces water, though it strongly affects climate and ecosystems.
The number that matters is local
Subsidence from groundwater withdrawal or sediment compaction can worsen relative rise; post-glacial uplift can offset it. Storm surge and waves ride on the changing baseline, so modest average rise can make damaging high-water events more frequent.
What people usually ask
Is sea level the same everywhere?
No. Gravity, winds, currents, temperature and land motion produce regional and local differences.
Does melting sea ice raise sea level?
Its direct effect is small because floating ice already displaces water. Melting land ice is the major added-water source.
Here’s where the answer came from
Open the original government science or research-institution source behind this page.