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Changing Sea Levels - causes and effects

Effects of sea level change.

Click on the map to explore the effects of changing sea level on the modern coastlines. The interactive maps will allow you to change sea level by fixed amounts, by known past change extremes or by observing the effects of melting the various large ice sheets.

Oceania India Africa Europe Asia South America Central America North America

Causes of sea level change.

The Earth's climate and global sea level are closely linked. As the earth warms up the sea level rises due to two major processes: the thermal expansion of ocean water and the reduction in volume of the glaciers and ice sheets.

Thermal Expansion:

As the ocean warms, the density decreases, so that even at constant mass the volume of the ocean increases. The thermal expansion of water accounts for a large portion of the change in sea level and is dependent upon changes in atmospheric temperature. Global warming has had the effect of increasing thermal expansion. The vast amount of greenhouse gases, such as carbon dioxide and water vapor, released into the atmosphere has led to a greater amount of heat absorbed in the infrared. These gases then reradiate this energy and direct some of it back toward the earth's surface, leading to small increases in global temperature and an expansion of the ocean's volume.

Over the course of the twentieth century, thermal expansion has contributed to sea level rise by .3 to .7 mm/yr. In the future, thermal expansion is expected to be the largest contributor to sea level rise over the next hundred years; it will lead to a .11 to .43 m rise.

Melting Glaciers and Ice Sheets:

A glacier, ice cap or ice sheet gains mass by accumulation of snow transformed to ice and loses mass (ablation) by melting, runoff, and evaporation. The melting of glaciers and polar icecaps, due to warming temperatures, leads to a rise in sea level. Over the 20th century, the melting of glaciers and ice caps has contributed about .2 to .4 mm/yr to sea level. According to the IPCC, ice sheets will continue to react to climate warming and contribute to sea level rise for thousands of years even after current climate changes have been stabilized. Sea level has been rising steadily, about 1-2 mm/year, since the end of "Little Ice Age" in the 19th century. This has resulted from the reduction in volume of ice caps, ice fields, and mountain glaciers, in addition to thermal expansion. However if current increases in global temperatures continue or accelerate due to global warming, many of the world's mountain glaciers will disappear.