Extraordinary Thawing of Greenland’s Ice
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)
