May 13, 2014

A huge area of the West Antarctic Ice Sheet appears to have begun a gradual but “unstoppable” slide into the sea, according to two new studies. The findings are the first firm evidence that this section of the ice sheet, which currently poses the largest threat of rapid sea-level rise, is in an “irreversible decline.” The loss of ice there, scientists have warned, is the first step in a chain reaction that could contribute significantly to higher-than-predicted global sea levels over centuries. Moreover, said scientists involved in the research, the simulanteous retreat (shrinking) of ice over such a large area suggests that the process was triggered by a common cause, which they link, in part, to global warming.

The first study, by scientists from the University of California, Irvine, and NASA’s Jet Propulsion Laboratory, is based on 40 years of observations of six glaciers bordering the Amundsen Sea. Since 1973, the amount of ice released by the glaciers has risen 77 percent annually, an amount nearly equal to the ice entering the ocean each year from the entire Greenland Ice Sheet. The leading edges of these glaciers, called tongues or ice shelves, float on seawater. The point where a glacier loses contact with the underlying terrain and begins to float is called the grounding line. Nearly all the melting takes place on the underside of a glacier beyond this line, where the ice comes into contact with warm seawater.

The scientists found that the speed of the Amundsen Sea glaciers flowing downhill from the center of the ice sheet has increased over the past 40 years. In addition, the glaciers’ grounding lines have been retreating. This means that sections of the glaciers are now floating above places they used to touch. The grounding line for the Pine Island Glacier, for example, retreated by 19 miles (31 kilometers) between 1992 and 2011.

The second study involved advanced computer modeling of the Thwaites Glacier, one of the six glaciers in the NASA study. Scientists had thought this glacier would remain stable for thousands of years. However, said glaciologist Ian Joughin of the University of Washington, Seattle, “this glacier is really in the early stages of collapse.” Its grounding line retreated by nearly 9 miles (14 kilometers) from 1992 to 2011.

Glaciers in the NASA study appear in red. The darker the color, the faster the speed at which the glaciers are flowing toward the Admundsen Sea. (Image credit: Eric Rignot)

The retreat of a grounding line could be the first step in a chain reaction. In this process, as the line retreats, the glacier gets thinner. As the ice grows thinner, it offers less resistance to the water and flows faster. The glacier also loses its ability to hold back inland glaciers flowing toward the sea. These glaciers, in turn, grow thinner and flow faster. The result is more ice flowing into the sea and rising sea levels.

Scientists are still uncertain about the timeline for the collapse of the Amundsen Sea glaciers. The NASA scientists estimated that it could take as few as 200 or as many as 900 years for all the ice in the glaciers to melt. That meltwater would be enough to raise all sea levels by 4 feet (1.2 meters). According to a recent report by the United Nations Intergovernmental Panel on Climate Change, sea levels are projected to rise from 1 to 3 feet (26 to 98 centimeters) by 2100. However, most projections of sea-level rise do not take into account ice loss from West Antarctica. The findings from the new studies, the NASA scientists say, suggest that these projections should be revised upward.

Additional World Book articles:

• Antarctica: The Hidden Continent (a Special Report)
• Meltdown: Climate Change in the Arctic (a Special Report)
• The Great Meltdown (a Special Report)

July 11, 2013

An iceberg slightly larger than the city of Chicago has finally calved (broken away) from Antarctica’s Pine Island Glacier (PIG), two years after scientists first spotted a 15-mile (24-kilometer) crack in the PIG’s ice shelf. (An ice shelf is the foreward part of an ice sheet that floats on water.) The PIG, located in West Antarctica, is shrinking faster than any other glacier on Earth. It also ranks number one among glaciers whose melting is contributing to the rise of global sea levels. The new iceberg, which has a surface area of 278 square miles (720 square kilometers), is now floating in the Amundsen Sea.

Scientists with NASA’s Operation IceBridge first noticed a crack in the PIG’s ice shelf in October 2011 while flying over and surveying the massive glacier. The crack, then about 15 miles (24 kilometers) long and 164 feet (50 meters) wide, had grown to 17 miles (28 kilometers) long and 1,770 feet (540 meters) at its widest point just before the iceberg split off, according to scientists at the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany. Scientists at the institute have been tracking the birth of the iceberg using the German Space Agency’s TerraSAR-X satellite.

The new iceberg that calved from the Pine Island Glacier appears in a satellite image from the German Space Agency on 8 July 2013. (DLR)

Calving is a natural process for Antarctic ice sheets and is not necessarily related to global warming. The PIG produced huge icebergs in 2001 and 2007. However, scientists have found that the PIG has grown significantly thinner and has begun to move faster toward the sea in recent decades. The glacier is currently responsible for about 10 percent of all the ice flowing into the sea from West Antarctica.

The new iceberg, however, did not set any records for size. In March 2000, one of the largest icebergs ever recorded separated from the Ross Ice Shelf. Named B-15, it was around 4,250 square miles (11,000 square kilometers) in surface area—about the size of the island of Jamaica—and possibly more than 1,000 feet (300 meters) thick. Even after drifting into the warmer waters of the Southern Ocean and breaking apart, some pieces survived more than 10 years. In January 2005, a huge chunk of B-15 ran aground in Antarctica’s McMurdo Sound in the Ross Sea, devastating Adélie penguin colonies. The iceberg prevented adult Adélie penguins from feeding in normally open waters. Many penguin chicks died of starvation while their parents trudged across the vast ice sheet in search of food.

Additional World Book articles:

• Amundsen, Roald
• Ice formation
• Ross Dependency
• The Great Meltdown (a special report)
• Science in Antarctica (a special report)

December 28, 2012

The West Antarctic Ice Sheet is warming significantly faster than scientists had estimated, according to a study published in the journal Nature Geoscience. The authors of the study revealed that the average temperature at a research station in the middle of West Antarctica has risen by 4.3 Fahrenheit degrees (2.4 Celsius degrees) since 1958–roughly twice as much as scientists previously believed and three times the overall rate of global warming. Particularly surprising was the discovery that although most of the Antarctic warming took place as expected in the spring (September, October, and November in the Southern Hemisphere), some warming occurred in the summer (December, January, and February). Scientists had thought that temperatures in the Antarctic remained relatively stable during the summer.

This alarming report follows another recent study, which found that melting in West Antarctica has accelerated by about 50 percent since 1992. That study, published in November by 47 climate scientists from 26 labs around the world, also found that Greenland’s ice sheets are melting at a rate five times faster than they were in the 1990’s.

Ice and snow cover 98 percent of Antarctica, the world's coldest region. (© Rod Planck, Photo Researchers)

The West Antarctic Ice Sheet is the part of Antarctica that lies west of the Transantarctic Mountains and is mainly in the Western Hemisphere. Because of the enormous weight of the ice there, the terrain under the ice sheet is an average of 3,300 feet (1,000 meters) below sea level. At the ice sheet’s edge near the Southern Ocean, broad, flat, floating ice shelves fill several of Antarctica’s bays and channels. Those ice shelves, along with the ice in the interior, comprise about 90 percent of the world’s ice. Scientists have calculated that if all of Antarctica’s ice melted, Earth’s oceans would rise nearly 230 feet (70 meters), flooding coastal cities around the world. The November study of ice sheets in both polar regions found that the melting there has caused nearly a ½ inch (11 millimeters) rise in in sea level since 1992, or about 20 percent of the overall rise.

One of the scientists involved in the new study, Andrew J. Monaghan of the Colorado-based National Center for Atmospheric Research, noted “When you see this type of warming, I think it’s alarming.”

Additional World Book articles:

• Exploration (the Exploration of Antarctica)
• Glacier
• Global warming (2009) (a Back in Time article)
• The Great Meltdown (a special report)
• Science in Antarctica (a special report)

July , 2012

A huge canyon nearly as deep as the Grand Canyon has been discovered beneath a remote area of the West Antarctic ice sheet, a team of British scientists has reported. Scientists think that the canyon, which lies buried under nearly 1 mile (1.6 kilometers) of ice, may be a major reason for the dramatic loss of ice from West Antarctica over the past 20 years. The previously unknown canyon, named the Ferrigno Rift, lies beneath a massive glacier known as the Ferrigno Ice Stream, located just west of the Antarctic Peninsula. Satellite data collected over several decades has documented both a significant drop in the depth of the ice stream as well as an increase in the amount of ice breaking off into the Southern Ocean, which surrounds Antarctica. Scientists have calculated that melting ice from West Antarctica is responsible for nearly 10 percent of the current rise in global sea levels.

(World Book map; map data © MapQuest.com, Inc.)

The canyon was discovered by scientists from the University of Aberdeen in Scotland, who spent a brutal nine weeks measuring the topography of the ice stream’s rocky base using ice-penetrating radar devices hitched to snowmobiles. Glaciologist Robert Bingham of Aberdeen said that the dropoff in his measurements of the depth of the ice was so startling that he drove over the area two or three times to confirm his data.

Antarctica's rugged coast features jagged mountain peaks and glacier-filled valleys. Ice and snow cover 98 percent of the continent. Antarctica is the world's coldest region. (© Rod Planck, Photo Researchers)

An analysis of the data by Bingham and colleagues from the British Antarctic Survey indicate that the Ferrigno Rift is about 6 miles (9.6 kilometers) wide and at least 62 miles (100 kilometers) long. The Grand Canyon is more than 1 mile deep, 277 miles (446 kilometers) long, and from less than 1 mile to 18 miles (29 kilometers) wide. Unlike the Grand Canyon, the Ferrigno Rift was created when sections of Earth’s crust in what is now West Antarctica separated, creating a valley. Erosion likely deepened the valley, which probably formed tens of millions of years ago when Antarctica was ice free. The Grand Canyon was created chiefly through erosion by the Colorado River.

Bingham reported that the rift may be speeding the movement of the Ferrigno Ice Stream to the sea in several ways. Glaciers move more quickly over sediments like those found near the bottom of the rift. In addition, water from the Southern Ocean, which appears to be warming faster than any other ocean, may be flowing into the rift, causing erosion of the glacier from below.

Additional World Book articles:

• Global warming
• Ice formation
• Icecap
• Science in Antarctica (a Special Report)
• The Great Meltdown (a Special Report)