Columbia Glacier: A Swift Retreat
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|Floating icebergs that calved from the edge of the glacier fill Columbia Bay. Courtesy of NASA/Jon Von Atta, 2008|
Water, water everywhere. Our planet has more surface covered with water than land, and some of that water has been held in cold storage. Glaciers, such as the Columbia Glacier in Alaska, both record Earth’s climate in their dense layers of ice and affect the climate itself when their white surfaces reflect solar radiation back into space.
In a series of images from 1986 to 2011, taken with Landsats satellites 4, 5, and 7, the Columbia Glacier in Alaska’s Chugach Mountains is in decisive retreat. The false-color image shows ice in blue and vegetation in green. The dark blue that represents ocean water has opened and crept 12 miles (20 kilometers) up the mountain where the glacier used to be. The Columbia Glacier is a tidewater glacier and, as such, enters the sea. These types of glaciers have retreated rapidly during the last century.
The Columbia Glacier is only one point in a trend Landsat has witnessed over the past 40 years: glaciers are retreating all over the world — a clear consequence of contemporary climate change. According to a 2009 study by the U.S. Geological Survey, 99 percent of American glaciers are shrinking.
Glaciers grow by snow added in their upper part, also known as the accumulation area, and shrink by loss of ice through melting in their lower part, known as the wastage area.
Glaciers tell a story of climate conditions — advancing when temperatures are cool enough to conserve glacial ice and receding when temperatures cause melting. Glaciers advance and retreat from season to season, so it takes observations over decades tell whether a glacier is generally expanding and advancing or shrinking and retreating.
There once was a time when vastly more of our world was coated with ice. During the Pleistocene Ice Age, at times an estimated 30 percent of the land was ice covered, all that trapped water meant that there were lower sea levels worldwide. In places, there was so little water, bridges of land opened up and created passageways for migrating humans.
Today, the opposite is happening. About 10 percent of Earth’s surface is covered in glaciers and ice sheets, holding less than 2 percent of our planet’s water. And glaciers are melting, releasing their water and contributing to sea level rise. With one third of the world’s seven billion people living at or near a coastline, these rising seas could have serious consequences.
NASA and the U.S. Department of the Interior, through the U.S. Geological Survey (USGS), jointly manage Landsat, and the USGS preserves a 40-year archive of Landsat images that is freely available over the Internet. The next Landsat satellite, now known as the Landsat Data Continuity Mission (LDCM) and later to be called Landsat 8, is scheduled for launch in 2013.