The Basics | Local Sea Level Change – Global Sea Level Change

Relative sea level is the height of the ocean compared to the land next to it. Local sea level is generally given as this relative value.
Local sea levels depend on changes in land height, ocean currents, and other factors in addition to changes in the global sea level.
In some places, like the U.S. Gulf Coast and the western tropical Pacific, sea levels are rising faster than global sea level.
Impacts from temporary changes in sea level during high tides and storms are getting worse for areas where sea level is rising.

Global vs. Local Sea LevelGlobal Versus Local Sea Level

The global sea level is the average ocean height across the entire planet. It gives an overall picture of how sea levels are changing and how the ocean is responding to global warming. Local sea level refers to the sea level at a specific location. It is often considered synonymous with relative sea level, which is the height of sea level compared to the land next to it. The local sea level depends on many factors. Changes in land height, ocean currents, and other natural factors all play a role. In some places, local sea level rise can differ from the global rise by 100% or more.

Sea Level Snippets

Even though there are regional variations, sea level has risen almost everywhere across the globe in the past three decades. From satellite measurements, we know that the sea level has risen in 98% of the ocean from 1993 to present.
So much ice is being lost from the ice sheets that it is impacting the rotation, shape and gravity of Earth. These shifts are causing locations that are close to where the ice is melting actually feel less of the resulting sea level rise than locations further away.

Factors Affecting Local Sea LevelLand Height, Ocean Currents, and Other Factors Affecting Local Sea Level

The illustration shows causes of local sea level change. There are three houses on the left on top of the land. The land has arrows up and down that show vertical land motion. In the middle bottom are white wavy lines to show changes in ocean currents. In the middle top there are arrows pointing up with more blue water showing global sea level rise. On the middle right is a grayed out box that shows a cloud with white lines coming down for rain to highlight temporary changes from tides, storms, and other natural changes. On the right side of the image is an illustration of a melting glacier on land with a lower water level showing the movement of water from melting glaciers to the tropics. — Global sea levels are rising due to climate change. However, the height of the ocean locally also depends on other factors such as vertical land motion and changes in ocean currents. Additionally, Earth's gravity causes impacts from melting of ice sheets and glaciers that move water away from the glaciers and toward the tropics. Tides, storms, and other natural changes (e.g. El Niño) can also alter the local sea level temporarily, but these stack on to the background sea level height at the time of the event. Credit: Allie Braun/NASA JPL.

Over years, land can move up or down. This land movement is called vertical land motion. The land moves up and down from natural causes, such as tectonic plates moving or sediment settling, and human causes, like pumping out groundwater or removing fossil fuels from the ground causing land to sink. When land rises, it is referred to as uplift. When it sinks, it is called subsidence.

When the land next to the ocean sinks, it has the apparent effect of the sea level going up faster in that area. Conversely, when the land rises, it can cause the sea level relative to land to stay constant or go down.

Changes to ocean currents from climate change can also play a role in local sea level rise over time. Ocean currents are like rivers in the sea and help transport heat around the planet. Warmer water and added freshwater from rapidly melting ice sheets to the ocean impact the ocean currents causing them to shift their speed or location slightly. These shifts can then impact the sea levels in a particular area. These changes are part of what is called sterodynamic sea level change. This is the combined effect on sea level from changes in the ocean’s temperature, saltiness, and motion.

These local and regional changes impact how fast sea levels are rising in that area. That’s because these happen in addition to global sea level rise. So if the land is sinking next to rapidly warming waters, that local sea level will often rise faster than the global sea level.

Over hours or days, tides and weather also make local sea levels rise and fall temporarily. These wiggles happen on top of the starting sea level height. For many areas, as the starting sea level rises each year due to climate change, the impacts from tides and storms are getting worse.

Temporary ups and downs in sea level have always happened. These come from things like regular daily tides, and natural year-to-year fluctuations such as El Niño. The rises and falls can also potentially be very big from passing storms. In the past, most of these regular ups and downs have not caused problems or led to flooding. Now with sea level rise, the temporary increases are leading to more frequent and more severe flooding. This will continue to worsen in the future as sea level rise continues.

Dive Deeper: More about the factors that cause sea level to change locally.

About Sea Level Change

What Causes Local Sea Level Change?

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Global vs. Local Sea LevelGlobal Versus Local Sea Level

Factors Affecting Local Sea LevelLand Height, Ocean Currents, and Other Factors Affecting Local Sea Level

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