Which processes contribute to sea-level change on short and long timescales?

• A. Changes in coastline height from thermal expansion, ice-volume changes, and tectonics.
• B. Sea-level remains constant; only local land movement matters.
• C. Gravitational effects from the Moon drive most long-term sea-level shifts.
• D. Tectonics alone determine sea-level without climate influence.

Answer: (A)

Sea-level change on both short and long times is driven by changes in how much water sits in the oceans and by how the land itself moves. When seawater warms, it expands, so the ocean volume effectively increases and global mean sea level rises, often on shorter timescales as temperatures respond to climate fluctuations. Over longer periods, the amount of water in the oceans changes with ice storage on land—ice sheets and glaciers growing stores water on land and melting returns it to the oceans—altering global sea level.

At the same time, the land can rise or sink due to tectonic forces and the slow rebound of the crust after ice ages. This vertical movement of the coastline changes how high the land sits relative to the sea, shifting the coastline itself even if the ocean’s volume remains the same.

Putting these together, changes in ocean volume from thermal expansion and ice-volume fluctuations, along with tectonic uplift or subsidence, explain sea-level change across short and long timescales. The Moon’s gravitational effect shapes tides locally, but it doesn’t drive long-term sea-level trends, and sea level is not determined by tectonics alone without climate influences.