Why isn’t the rate of sea level rise the same everywhere?

The global sea level is the average ocean height across the entire planet. It gives an overall picture of how sea levels are changing. Local, or relative, sea level is the height of the ocean 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. When factored in, sea level rise locally can differ from the global rise by 100% or more.

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 the land next to the ocean sinks, it can cause the sea level to go up faster in that area. Conversely, when the land rises, it can cause the sea level to stay constant or go down. Both of these can impact the height of the local sea level and how quickly it is changing.

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, salitness, and motion.