Why will sea levels rise?

Answer 1

The earth is going through a period of warming, known as global warming. As the earth becomes warmer the Ice in very cold parts of the world begins to melt. Instead of floating on top of the water in solid form, this now melted water goes (diffuses) into the ocean, causing the seal level to rise.

Answer 2

As glacial ice melts it tends to end up in the oceans. Much of the arctic ice is already afloat, so its melting contributes very little to sea rise. There will be some rise due to thermal expansion of ocean water. However, Greenland bears enough ice to raise ocean levels close to 20 feet.

Antarctica has enough ice to raise ocean levels 200 feet, though this ice is not expected to melt for centuries.

Answer 3

Sea Level is rising for two reasons:

1. The ocean is warming. It warmed approximately one degree last century. As water warms it expands*. Thus the simple warming of seawater causing the sea to rise slightly. This century it is estimated that sea level will rise approximately 6-8 inches (20 cm) due to the overall warming. This effect, called "thermal expansion" is extremely small in percentage terms. But with the average global ocean depth in excess of two miles (3 km) even that minuscule amount will cause that increase this century.

2. Ultimately the larger cause of sea level rise is the melting ice sheets and glaciers, which flow into the sea, causing it to rise in height. This is not to be confused with the melting sea ice around the north pole. That is floating ice. As it melts, it does not add to the height of the ocean, just as floating ice cubes in a glass will not affect the level of the liquid (Archimedes Principle).

But the ice sheets on Greenland and the Antarctic (South Pole) are miles thick and are on firm ground. As they melt they will have dramatic effect on sea level. The melt rates are increasing due to the recent warming. If Greenland were to melt entirely, it would raise global sea level approximately 7 meters (23 feet). If the Antarctic were to melt entirely it would raise sea level by approximately 70 meters (240 feet). Fortunately even the most aggressive estimates for global warming indicate that it will take many centuries, possibly longer than a thousand years for those two ice sheets to melt entirely.

The glaciers, which are found on all the continents, are also noticeably disappearing at unprecedented rates. But the potential effect on rising sea level is modest, on the order of 30 cm (1 foot).

* Generally water expands as it warms, the same as nearly all substances. Water however has one quirky characteristic, that is almost critical for life on earth. Just above the freezing point, liquid water is actually more dense than ice. This is the reason that ice floats. If it did not, ice would sink to the bottom of lakes and other bodies of water. Scientists believe that would likely have killed many early forms of developing life and even most aquatic life in the modern era.