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Glacier and Landscape Change in Response to Changing Climate

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Glaciers and Sea Level

see caption
Grinnell Glacier in Glacier National Park, Montana; photograph by Carl H. Key, USGS, in 1981. The glacier has been retreating rapidly since the early 1900's. The arrows point to the former extent of the glacier in 1850, 1937, and 1968. Mountain glaciers are excellent monitors of climate change; the worldwide shrinkage of mountain glaciers is thought to be caused by a combination of a temperature increase from the Little Ice Age, which ended in the latter half of the 19th century, and increased greenhouse-gas emissions.

Worldwide, most mountain glaciers have been retreating since the end of the "Little Ice Age". Although this date varies from region to region, in most locations, retreat was underway by the late 1800s. As a consequence of glacier meltwater entering the global ocean, global sea level has risen about 30 centimeters (about one foot). Glaciers vary in size in response to changes in global and regional climate.

Sea-level changes, especially in densely populated, low-lying coastal areas and on islands, have significant effects on human activities and facilities. The present volume of the Earth’s glacier ice, if totally melted, represents about 80 meters in potential sea-level rise.

The geologic record documents that glaciers have existed on Earth for billions of years. During that time, glaciers have repeatedly expanded and shrunk in response to changes in global and regional climate. During glacial stages (ice ages), periods of time dominated by colder climate, global sea level was lowered by as much as 200 meters. This is the result of water evaporating from the oceans being precipitated as snow and frozen into continental scale glaciers

About 21,000 years ago, during the last glacial maximum (LGM), sea level was about 125 meters (about 410 feet) lower than it is today.

About 125,000 years ago, during a warmer climatic interval in the last interglacial stage, sea level was about 6 meters (about 19.7 feet) higher than it is today.

About 2.2 million years ago, during an even warmer inter­val, sea level is estimated to have been 25 to 50 meters (about 82 to 164 feet) higher.

Less than 20,000 years ago, during the last phase of the Pleistocene, the Last Glacial Maximum (LGM), glaciers covered:
            ~ 8 % of Earth's surface
            ~ 25 % of Earth's land area
            ~ 30% of Alaska.

Following the LGM (beginning ~ 15,000 yr B.P.), continental glaciers retreated and sea level began to rise.  By ~ 6,000 yr B.P. sea level reached its current height. It has fluctuated ever since.
 
Today, glaciers cover:
            ~ 3.1 % of Earth's surface,
            ~ 10.7 % of Earth's land area
            ~ 5 % of Alaska.

For more information visit the USGS Web site Sea Level and Climate.


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Page Last Modified: Wednesday, May 30, 2012