What Are the Causes of a Rise in Relative Sea Levels?

Relative sea level change is the visible change in water level in relation to the land. While climate change and human interference is the most common scapegoat, other causes exist as well. The rise and fall of sea levels is not a new phenomenon. It is important to understand that not every worldwide change is caused by humans.

Global Warming

• Global climate change has had an effect on the relative rise of sea levels. A rise in the average temperature worldwide has caused glaciers to melt and add volume to the oceans. At the same time, oceans warm up and expand. As of 2011, relative sea levels are rising at a rate of 0.07 inches per year, which has a profound effect on low-lying coastal areas.

Land Changes

• Despite humans' role, sea levels have been rising and falling for millions of years. One natural reason is the change in land masses. Some areas are falling, causing the relative sea level to rise. Alternately, many land areas are rising, resulting in the opposite effect. These changes, however, are usually slow and not as dramatic as with climate change.

Ocean Currents

• Another lesser-known cause is the ocean currents. Like the land, ocean currents shift and move over time at varying rates. Sometimes these changes result in eddies. Eddies are currents that run against the main current, influencing their direction. As the currents shift, so do relative sea levels. Additionally, temperature changes can also affect the currents, further altering sea levels.

Human Interference

• Human influence on relative sea levels is not exclusively related to climate change. When people extract groundwater or oil from a deposit, the earth compresses to fill the empty reservoir. As the ground level falls, the relative sea level rises. This has been particularly noticeable in the coastal areas of China. It is the same case with river deltas, where the compression of sediments causes the land to drop.