Ocean levels have changed throughout geologic time. During the last ice age, the sea level was as much as 30 meters lower than its current levels. During interglacial periods, such as present times, the ocean level has risen by as much as 10 meters higher than today, which has caused most of Florida to be covered by water. Scientists calculate that if all the glaciers and ice caps melted, the ocean level would rise by 70 meters. They also admit that this is not a probable event. During the last ice age, broad grasslands emerged on continental shelves and it was possible to walk from Siberia to Alaska.

Most of the changes in ocean water level are the result of an increase or decrease in water stored within glaciers and ice caps. Due to global warming the melting of glaciers and icecaps causes the sea level to rise about two millimeters per year. This melting has resulted in a 10 centimeter rise in sea level over the last 50 years. Many scientists predict there will be an increase in the ocean level of approximately 30 centimeters or more in the next 50 years. This prediction has been attributed to global warming, but many disagree about exactly all the causes that result in the recent rise in sea level. The water cyclestores much of Earth's water in the ocean and as frozen water. Many argue that the only important process is global warming, which causes melting ice caps and glaciers to transfer water to the oceans. Others notice that increased temperatures will increase evaporation, which increases snow formation and increases glacier and ice cap building. No matter what the reasons for the ocean rising, the increased levels already have and will cause flooding in many communities near the coastal shorelines.

Use the water cycle illustration at the right to determine how you believe that increasing global temperature will affect sea level. As you look at the diagram, answer the following questions:

1. What happens to ocean levels as the world's glaciers and ice caps increase in size?
2. What happens to ocean levels as the world's glaciers and ice caps decrease in size?
3. What would rising temperatures do to evaporation, condensation and participation rates?
4. What factors cause glaciers and ice caps to increase or decrease in size?

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Updated October 24, 2008 by: Glen Westbroek