Introduction
Sea level is one of the world's biggest concerns since the global warming theory became popular. The majority of people believe that if the temperature of the globe warms then the ice caps in both Greenland and West Antarctica will melt causing the sea level to rise by 20-40 feet. Although the ocean is filled with water; it is not water that decides sea level.
Atmospheric Pressure
Sea level is not dependant on how much water is in the oceans, it is dependent on atmospheric pressure, and gravity. Lower in the atmosphere there is more atmospheric pressure, but the higher in the atmosphere the less atmospheric pressure. On Earth water evaporates quicker with less pressure and slower with more pressure. This means that even if all of the ice in Greenland and West Antarctica melted then the sea level would stay the same, because to stay in a liquid state water needs the higher atmospheric pressure exerted at sea level rather than at 20-40 feet above sea level. Now this brings up a problem; if water evaporates above sea level how come there are lakes and streams that exist above sea level. Lakes, ponds, reservoirs, and streams that are present above sea level usually have a constant source of water such as rain, but they still do evaporate more than if they were located at sea level.
Mysterious Disappearing Islands
In areas of the world like Indonesia, the islands that comprise the nations in that region are disappearing. There are several that argue sea level rise is to blame because of this. Well, usually these islands sink lower into the ocean after major earthquakes. Besides sea level, we need to analyze land levels. There are things called tectonic plates that comprise the Earth's crust, their movement causes earthquakes, volcanic eruptions, and tsunamis. Tectonic plates shift and when they do they can pull entire continents in different directions changing their shape over millions of years, they can cause mountain ranges to develop, and yes they can cause islands to disappear.
The islands in and near Indonesia and above Australia are sitting partly on the Australian plate while some are sitting on the Eurasian plate. The Australian plate is sub-ducting under the Eurasian plate, and is taking the islands in this region with it. This is what caused the tsunamis in December 2004. Eventually these islands will be completely gone.