Understanding Sea Level

Key Indicators

Global Mean Sea Level

What is global mean sea level?

This is the average height of the entire ocean surface. Global mean sea level rise is caused primarily by two factors related to global warming: the added water from melting land-based ice sheets and glaciers and the expansion of seawater as it warms.

What are we looking at?

The plot shows global change in sea level since 1992, as observed by satellite altimeters. The black line tracks the measurements, while the blue line shows how much uncertainty is associated with these measurements. Data shown are the latest available, with time needed to allow for processing (a lag of up to 4 months).

Why do we care?

Global mean sea level is an important climate indicator, providing information on how the ocean is warming and how much land ice is melting. Global sea levels have been rising for decades in response to a warming climate, and that rise appears to be accelerating.

Reference: Beckley et al., 2017; GMSL dataset


Satellite Altimetry (TOPEX/Poseidon and Jason I, II, III)


Data source: Satellite sea level observations. Credit: GSFC/PO.DAAC
Rate of Change
(± 0.4) mm/yr
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Sea level trends (1993-2016) For over 27 years, satellite altimeters have measured the sea surface height of our ever-changing oceans. This image shows the change in sea surface height across the globe from 1993 to 2019. Credit: NASA

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