September 24, 2012

Arctic sea ice melted to unprecedented levels in September, smashing all previous records. The sea ice reached its yearly minimum size on September 16, 2012, according to scientists with the National Snow and Ice Data Center (NSIDC). At that time, the sea ice covered 1.32 million square miles (3.41 million square kilometers), an area 18 percent smaller than ice cover at the last previous record, which was set in 2007. The NSIDC, located in Boulder, Colorado, is affiliated with NASA, the National Oceanic and Atmospheric Administration, and the University of Colorado.

Each year, Arctic sea ice grows and shrinks in area with the changing seasons. The sea ice reaches its largest area in March. It shrinks through the spring and summer, reaching its smallest size in September. It then grows through the fall and winter. This year, the ice shrank by 4.57 million square miles (11.83 million square kilometers) between March and September. That is the largest loss ever recorded, exceeding every other year by nearly 400,000 square miles (1 million square kilometers). The 2012 record was 49 percent smaller than the long-term average from 1979 to 2000, an area nearly twice the size of Alaska.  Arctic sea ice has deteriorated rapidly in recent years. In fact, all of the six lowest years for sea ice cover have occurred in the last six years.

Floating ice covers much of the Arctic Ocean’s surface. Most of the ice is sea ice (frozen seawater) that drifts with the currents. The rest is freshwater glacial ice, which breaks off from glaciers along the coasts of Arctic lands. Chunks of glacial ice form icebergs, seen in the distance in this photo. (© Corbis/SuperStock)

The 2012 record is all the more remarkable because summer weather in the Arctic was cooler than in 2007, the previous record-breaking year. In 2007, unusual warmth in the Arctic caused rapid melting. In contrast, the most important factor in 2012 was the thin, weakened ice itself. After many previous years of melting, much of the sea ice is new and thin. Such ice is more vulnerable to melting than older, thicker ice. In addition, a strong storm in early August helped to break up the weakened ice. Climate scientists warn that the Arctic Ocean could soon be entirely free of ice in the summers, possibly as early as 2015 to 2020.

Melting sea ice does not contribute to rises in sea level, because the ice is already floating on ocean water. However, scientists in 2012 also recorded unprecedented melting in Greenland, which does contribute to rising sea levels. NASA announced that 97 percent of the ice sheet in Greenland was melting during part of July. Scientists had never before measured such widespread melting. In the United States, July was the warmest month ever recorded, dating back to 1896.

Additional World Book articles:

• Global warming
• Greenhouse effect
• Kyoto Protocol
• 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)

August 30, 2012

The extent of the Arctic icecap fell to a record low on August 26, reported scientists with the National Snow and Ice Data Center (NSIDC) in Boulder, Colorado. The icecap was measured at 1.58 million square miles (4.1 million square kilometers), below the previous record of 1.61 million square miles (4.17 million square kilometers) set on Sept. 18, 2007, and the lowest level since satellite measurements began in 1979. NSIDC scientists noted that the icecap normally reaches it lowest point only in mid-September of each year, so there is a possibility that the sea ice may melt even more. The icecap grows larger during the cold Arctic winter, reaching about 6 million square miles (15.5 square kilometers).

The extent of Arctic sea ice fell on Aug. 26, 2012 (right), to 1.58 million square miles (4.1 million square kilometers), lower than the previous record low of 1.61 million square miles (4.17 million square kilometers) on Sept. 18, 2007. (National Snow and Ice Data Center)

NSIDC scientists also reported that the thickness of the icecap is diminishing. Submarine measurements indicate that the Arctic icecap has lost 40 percent of its thickness since the 1980′s. Between the loss of area and thickness, the summer ice volume in the Arctic in the 2000′s is only about 30 percent of its volume in the 1980′s. Of the finding, Peter Wadhams of Cambridge University in the United Kingdom said, “This means an inevitable death for the ice cover, because the summer retreat is now accelerated by the fact that the huge areas of open water already generated allow storms to generate big waves which break up the remaining ice and accelerate its melt.”

Scientists commenting on the findings linked the low ice levels to rising global temperatures. According to NSIDC scientist Ted Scambos, “We’re in a declining trend because the Earth is getting warmer. … It’s going to continue to be a series of shrinking ice extents year by year. … We’re not going back.” Climate scientists believe that the warming is mainly a result of human activity. The ice affects climate and weather conditions far beyond the North Pole.

Additional World Book articles:

• What We Know About Global Warming (A Special Report)
• The Great Meltdown (Special Report)
• Global warming (2007) (a Back in Time article)