Local and regional sea level rise depends not only on how much water is contained in the ocean, but also on the rise and fall of the land, including underneath the ocean. Understanding vertical land motion is critical for appropriately predicting and responding to sea level change.
Why it matters
As the global climate continues to change, average global sea levels are expected to rise, however regional and local sea-level changes will have the largest impact on coastal communities. Changes in the elevation of both the sea surface and the sea ?loor affect local sea level. Tectonics (e.g., earthquakes), ground water withdrawal, sediment compaction, and the redistribution of water and ice around the globe can cause the ocean floor to move up or down: this is known as “vertical land motion”. While the size of these effects vary depending on location, the combination can contribute to very dramatic sea-level changes. Vertical land motion plays a large role in historic, present, and future sea-level change. Even in the absence of present day global warming, many locations would be experiencing sea-level rise due to vertical land motion. Therefore, understanding historical vertical land motion is one of the ?irst steps in making sea-level projections into the next century.