By sea level, we refer roughly to the height of the sea or ocean surface. Sea level increases when the volume of water in the ocean increases and vice versa. One of the chief environmental processes that control sea level is climatic change. For example, the rise in temperature across the globe can cause polar icebergs and glaciers to melt, and this can increase the sea level greatly. In fact, one of major threats of global warming of the earth we are facing nowadays is the rise in sea level, leading to submerging of coastal areas (which means loss of many things, including human life). Besides global rise in temperature, tectonic changes or earth crust mechanisms like movement of lithospheric plates, addition of crust layers, volcanic activity near oceanic ridges, opening, closing and widening of sea basins, etc. can also cause changes in the sea level. Such changes in the sea level are mostly expressed on a wider scale.
A relatively predictable phenomenon is “tidal currents”, which is nothing but periodic rise and fall of sea level. The processes that control tidal waves are gravitational forces manifested by the moon and the sun with respect to the rotation of the Earth. The moon is the key controller as it is much nearer to earth as compared to the sun. Other forces that bring a change in the sea level are storms, floods, cyclones, tsunamis, etc. Such sea level changes are, however, not necessarily permanent and happen locally.
Many things affect the rise and fall. Although, today, a major problem is that the glaciers from the artic are melting due to global warming. The earth ozone layer has a hole over the artic because of the many greenhouse gases that are emitted. These gases are harmful, and affect the ozone layer. The ozone layer helps regulate the energy from the sun, creating the temperatures we have. Although, a hole, will allow a significant amount of heat to enter. This heat is warming up the ice, causing it to melt. Ice melts into water, and the water level is rising. Although, water rising and falling is greatly affected by the moon's gravitional pull. This results in high tide and low tide throughout the day.
The two greatest factors that contribute to the sea level are glaciers and the moon.
The moon's gravitational pull on the earth creates rythmic rises and falls in the sea level. We call these tides.
Glaciers, however, are less consistent. Over half of earth's supply of fresh water is frozen in glaciers and ice caps. Ice caps are chunks of ice floating in the ocean. Because, they are already displacing their volume in water they do not contribute to sea levels. Glaciers are frozen bodies of water over land. When large amounts of glaciers melt they contribure to a rise in sea levels. More important than the actual volume of water they yield is their climatic effects. Glaciers help to reflect some of the sun's light. When there are less reflective surfaces the ocean begins to absorb sunlight and evaporate. Galcier melts can cause both rises and falls in sea level depending on their severity.