3.4: Sea Level Rise
Much of the melting ice described previously contributes to sea level rise. The only exception is sea ice. Since sea ice is already floating in the ocean, its mass is already represented in the current sea level and so its melting does not affect sea levels. Think of a large glass of ice water, filled to the brim, and left sitting on a table – as the ice melts, the glass will not overflow because the mass of the water contained in the ice is already represented in the level of water in the glass.
Sea level rise has been documented throughout the globe (Figure \(\PageIndex{1}\)) and is driven primarily by two factors: ice melt and warming. Warming of Earth’s surface causes ice systems to melt, which increases the amount of water in the ocean and thus increases the sea level. In addition, warmer water takes up more space, since molecules expand as they are heated. Consequently, a warmer ocean will have a higher level due to thermal expansion of water molecules. Together, these two factors contribute the majority of sea level rise. Historically, the primary mode of long distance travel for both people and supplies was via water; consequently many of the world’s major cities are coastal leading to serious concerns about rising sea levels and urban infrastructures. Additionally, low-lying island systems such as the South Pacific country of Vanuatu, whose mean elevation is less than a meter above sea level, are threatened with inundation as sea levels continue to rise.