Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 12:58 PM GMT on July 25, 2012
Son Nghiem of NASA's Jet Propulsion Laboratory in Pasadena, CA, was analyzing radar data from the Indian Space Research Organization's Oceansat-2 satellite last week when he noticed that 97% of Greenland appeared to have undergone surface melting on July 12--an event completely unprecedented in 30 years of satellite measurements. In a July 24 press release from NASA, Nghiem said, "This was so extraordinary that at first I questioned the result: was this real or was it due to a data error?" Multiple satellite data sets confirmed the remarkable event, though. Melt maps derived from three different satellites showed that on July 8, about 40 percent of the ice sheet's surface had melted, as a strong ridge of high pressure set up over Greenland. By July 12, the melting had expanded to cover 97% of Greenland. As I blogged about last week, temperatures at at the top of the Greenland Ice Sheet, 10,551 feet (3216 meters) above sea level, and 415 miles (670 km) north of the Arctic Circle, had risen above the freezing mark four times in the 12-year span 2000 - 2011. But in mid-July 2012, temperatures eclipsed the freezing mark on five days, including four days in a row from July 11 - 14. Interestingly, ice core records show that in 1889, a similar pronounced melt event occurred at the top of the Greenland Ice Sheet, and such events occur naturally about every 150 years. "But if we continue to observe melting events like this in upcoming years, it will be worrisome," said Lora Koenig, a NASA/Goddard glaciologist and a member of the research team analyzing the satellite data. Such an event could occur as early as this weekend: the latest wunderground forecast for the Greenland Summit calls for above-freezing temperatures to return again by Saturday through Tuesday, with a high of 36°F (2°C) on Tuesday. This would come close to the record warm temperature at Summit of 3.6°C set just two weeks ago. Exceptionally warm temperatures in Greenland this July have been made more likely by the fact that Arctic sea ice area has been at record low levels so far this month. Furthermore, the Greenland Ice Sheet has become darker this July than at any point since satellite measurements began (Figure 2), allowing Greenland to absorb more solar energy and heat up.
Figure 1. Extent of surface melt over Greenland's ice sheet on July 8 (left) and July 12 (right). Measurements from three satellites showed that on July 8, about 40 percent of the ice sheet had undergone thawing at or near the surface. In just a few days, the melting had dramatically accelerated and an estimated 97 percent of the ice sheet surface had thawed by July 12. Image credit: NASA.
Figure 2. The albedo (reflectivity) of the Greenland Ice Sheet at its highest elevations (2,500 - 3,200 meters, or 8,200 - 10,500 feet) has steadily decreased in recent years as the ice has darkened due to increased melting and dark soot being deposited on the ice from air pollution. This July, the high elevations of Greenland were the darkest on record, which helped contribute to the record warm temperatures observed at the Greenland Summit. Image credit: Dr. Jason Box, Ohio State University.
Video 1. Melt water from the record July temperatures in Greenland fed the raging Watson River, which smashed two bridges connecting the north and south of Kangerlussuaq (Sønder Strømfjord), a small settlement in southwestern Greenland. The flow rate of 3.5 million liters/sec was almost double the previous record flow rate.
Greenland's Petermann Glacier
Greenland's glaciers have seen significant changes in recent years, as they respond to warmer air and water temperatures. Northwest Greenland's Petermann Glacier has seen two massive calving events in the past two years, though it is uncertain if these events were caused by the warming climate. The most recent event came on July 16, 2012, when the glacier calved a 46 square-mile iceberg two times the size of Manhattan. The same glacier calved an iceberg twice as big back on August 4, 2010--the largest iceberg observed in the Arctic since 1962. The freshwater stored in that ice island could have kept the Delaware or Hudson rivers flowing for more than two years, or kept all U.S. public tap water flowing for 120 days. According to a university press release by Andreas Muenchow, associate professor of physical ocean science and engineering at the University of Delaware's College of Earth, Ocean, and Environment, “While the size is not as spectacular as it was in 2010, the fact that it follows so closely to the 2010 event brings the glacier’s terminus to a location where it has not been for at least 150 years. Northwest Greenland and northeast Canada are warming more than five times faster than the rest of the world, but the observed warming is not proof that the diminishing ice shelf is caused by this, because air temperatures have little effect on this glacier; ocean temperatures do, and our ocean temperature time series are only five to eight years long — too short to establish a robust warming signal.”
Figure 3. The massive 46 square-mile iceberg two times the size of Manhattan that calved from Greenland's Petermann Glacier on July 16, 2012, as seen on July 21, 2012, using MODIS satellite imagery. Image credit: NASA.
Record warmth at the top of the Greenland Ice Sheet (July 18, 2012)
Unprecedented May heat in Greenland; update on 2011 Greenland ice melt
Greenland update for 2010: record melting and a massive calving event
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