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)

November 30, 2012

Greenland’s ice sheets are melting at a rate five times faster than they were in the 1990’s, according to a new study of polar ice sheets reported in the journal Science. The study, which involved 47 climate scientists from 26 labs around the world, also found that the melting in West Antarctica has accelerated by about 50 percent. The only ice sheet that shows no signs of melting is in East Antarctica, the highest and coldest area on the planet. That ice sheet is actually growing, because rising temperatures have increased snowfall. Warmer air holds more water, so higher temperatures typically increase snowfall in cold areas. However, the small increase in ice there is not enough to offset the loss of ice from West Antarctica. The melting is being caused by global warming—the gradual increase in average temperatures at Earth’s surface. Most climate scientists have concluded that global warming is caused mainly by greenhouse gases released by burning such fossil fuels as coal and oil.

The study found that the melting ice sheets have caused nearly ½ inch (11 millimeters) of the rise in sea level since 1992, or about 20 percent of the overall rise. The scientists cautioned that it is difficult to determine how quickly sea level may rise in the future, largely because of uncertainties about how quickly glaciers will flow into the sea. But there is no question that the rise in sea level has also accelerated. Most climate scientists expect sea level to rise by 3 to 6 feet (1 to 2 meters) by 2100.

The retreat of a mountain glacier can provide visible evidence of global warming. These photographs show two late-summer views of Grinnell Glacier in Glacier National Park, Montana. In the photo taken around 1940, top, Upper Grinnell Lake had only begun to form at the glacier’s end. By 2006, bottom, melting ice had caused the lake to swell in size. Researchers predict that warming will melt all of the park’s glaciers by 2030. (Glacier National Park Archives, top; U.S. Geological Survey, photograph by Karen Holtzer, bottom.)

The new research provides more evidence that the Arctic is warming more quickly than any other area of the planet. In September, scientists at the National Snow and Ice Data Center reported the greatest melt of Arctic sea ice ever recorded. In fact, all six of the record-setting years for melting sea ice have occurred in the last six years. Melting sea ice does not add to rising sea level, because sea ice already floats on ocean water. But warming polar waters eat away at the edges of ice sheets on land, causing glaciers to flow into the ocean more quickly. Ice that melts from land does cause rising sea level.

The research helps to resolve scientific uncertainty about the rate of melting in the polar ice sheets. Different methods of measurement have found somewhat different rates of melting. The new research combined three different sources of data. The first was altimetry, which involves aircraft using lasers to measure the elevation of the ice sheet. Another source was satellites that measure ice using radar. The third source was satellites that measure tiny changes in Earth’s gravitational field. This field varies slightly depending on the mass of ice in a given location. Together, the three methods of measurement show the accelerating loss of polar ice.

Additional World Book articles:

• Kyoto Protocol
• Ice formation
• Intergovernmental Panel on Climate Change
• The Great Meltdown (a Special Report)
• Global warming (2011) (a Back in Time article)
• Global warming (2010) (a Back in Time article)

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)
  

July 25, 2012

A rapid warm-up in Greenland in mid-July caused melting at or near the surface over nearly 97 percent of the island’s massive ice sheet, data from three Earth-orbiting satellites have revealed. The speed and scale of the melt was so extraordinary that the scientist who discovered the event questioned the accuracy of the data. Such islandwide melting has not occurred since 1889. However, scientists are unsure whether the July event was a rare though natural occurrence or is related to the rise in global temperatures linked to human activity.

Normally, about 55 percent of Greenland’s surface ice cover melts to some degree by mid-summer. Measurements taken on July 8 showed thawed ice over about 40 percent of Greenland. But four days later, that area had increased dramatically to 97 percent. The melting affected even Summit station, the thickest, coldest point on the ice sheet, which sits about 2 miles (3.2 kilometers) above sea level. “Ice cores from Summit show that melting events of this type occur about once every 150 years on average. With the last one happening in 1889, this event is right on time,” said glaciologist Lora Koenig, a member of the research team analyzing the satellite data. “But if we continue to observe melting events like this in upcoming years, it will be worrisome.”

Melting at or near the surrface of Greenland's ice sheet rapidly expanded from 40 percent on July 8 to nearly 97 percent on July 12. (Credit: Nicolo E. DiGirolamo, SSAI/NASA GSFC, and Jesse Allen, NASA Earth Observatory)

The dramatic melt was first spotted by Son Nghiem of NASA’s Jet Propulsion Laboratory in Pasadena, California, while analyzing data from a satellite launched by the Indian Space Research Organisation (ISRO). Data from NASA’s TERRA and Aqua satellites and a United States Air Force weather satellite confirmed Nghiem’s finding. An unusually strong ridge of warm air that stalled over Greenland on about July 11 may have caused the thaw. This heat dome was one of a number that have dominated weather on Greenland since May.

Additional World Book articles:

• Ice formation
• Intergovernmental Panel on Climate Change
• Global warming 2009 (a Back in Time article)
  
• The Great Meltdown (a Special Report)