Unprecedented Greenland Ice Sheet Surface Melt

[Andrew Veresay]

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.

In the image, the areas classified as “probable melt” (light pink) correspond to those sites where at least one satellite detected surface melting. The areas classified as “melt” (dark pink) correspond to sites where two or three satellites detected surface melting. The satellites are measuring different physical properties at different scales and are passing over Greenland at different times. As a whole, they provide a picture of an extreme melt event about which scientists are very confident. Credit: Nicolo E. DiGirolamo, SSAI/NASA GSFC, and Jesse Allen, NASA Earth Observatory.

For several days this month, Greenland's surface ice cover melted over a larger area than at any time in more than 30 years of satellite observations. Nearly the entire ice cover of Greenland, from its thin, low-lying coastal edges to its two-mile-thick center, experienced some degree of melting at its surface, according to measurements from three independent satellites analyzed by NASA and university scientists.

On average in the summer, about half of the surface of Greenland's ice sheet naturally melts. At high elevations, most of that melt water quickly refreezes in place. Near the coast, some of the melt water is retained by the ice sheet and the rest is lost to the ocean. But this year the extent of ice melting at or near the surface jumped dramatically. According to satellite data, an estimated 97 percent of the ice sheet surface thawed at some point in mid-July.

Researchers have not yet determined whether this extensive melt event will affect the overall volume of ice loss this summer and contribute to sea level rise.

"The Greenland ice sheet is a vast area with a varied history of change. This event, combined with other natural but uncommon phenomena, such as the large calving event last week on Petermann Glacier, are part of a complex story," said Tom Wagner, NASA's cryosphere program manager in Washington. "Satellite observations are helping us understand how events like these may relate to one another as well as to the broader climate system."

Son Nghiem of NASA's Jet Propulsion Laboratory in Pasadena, Calif., was analyzing radar data from the Indian Space Research Organisation's (ISRO) Oceansat-2 satellite last week when he noticed that most of Greenland appeared to have undergone surface melting on July 12. Nghiem said, "This was so extraordinary that at first I questioned the result: was this real or was it due to a data error?"

Nghiem consulted with Dorothy Hall at NASA's Goddard Space Flight Center in Greenbelt, Md. Hall studies the surface temperature of Greenland using the Moderate-resolution Imaging Spectroradiometer (MODIS) on NASA's Terra and Aqua satellites. She confirmed that MODIS showed unusually high temperatures and that melt was extensive over the ice sheet surface.

Thomas Mote, a climatologist at the University of Georgia, Athens, Ga; and Marco Tedesco of City University of New York also confirmed the melt seen by Oceansat-2 and MODIS with passive-microwave satellite data from the Special Sensor Microwave Imager/Sounder on a U.S. Air Force meteorological satellite.

The melting spread quickly. Melt maps derived from the three satellites showed that on July 8, about 40 percent of the ice sheet's surface had melted. By July 12, 97 percent had melted.

This extreme melt event coincided with an unusually strong ridge of warm air, or a heat dome, over Greenland. The ridge was one of a series that has dominated Greenland's weather since the end of May. "Each successive ridge has been stronger than the previous one," said Mote. This latest heat dome started to move over Greenland on July 8, and then parked itself over the ice sheet about three days later. By July 16, it had begun to dissipate.

Even the area around Summit Station in central Greenland, which at 2 miles above sea level is near the highest point of the ice sheet, showed signs of melting. Such pronounced melting at Summit and across the ice sheet has not occurred since 1889, according to ice cores analyzed by Kaitlin Keegan at Dartmouth College in Hanover, N.H. A National Oceanic and Atmospheric Administration weather station at Summit confirmed air temperatures hovered above or within a degree of freezing for several hours July 11-12.

"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," says Lora Koenig, a Goddard glaciologist and 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."

Nghiem's finding while analyzing Oceansat-2 data was the kind of benefit that NASA and ISRO had hoped to stimulate when they signed an agreement in March 2012 to cooperate on Oceansat-2 by sharing data.

http://www.nasa.gov/topics/earth/features/greenland-melt.html

SHOCKING..

[an extreme effect of Earth Wobble, i guess. shows how extreme it is getting]

[jorge namour]

A canyon under Antarctica favours melting ice

(AFP) - There are 3 days

PARIS - A canyon near 1500 m depth would increase the phenomenon of ice melting in West Antarctica, report British researchers who discovered this huge valley through which water enters "hot" of the ocean under the ice cap .

"We report the discovery of a basin under the ice cap (...) to a depth of 1.5 km, connected with the ice sheet of the Inland Sea and Bellingshausen whose existence has a profound loss ice "West Antarctic, they explain in a study released Thursday by the British journal Nature.

The seven authors explain that the rift system of western Antarctica, constantly dug by erosion, let in water "hottest" of the ocean "thus promoting instability of the ice ice ".

The region where the canyon was discovered had not been researched for almost 50 years. In 2010 a mission project monitoring British Antarctic (BAS) has visited the country led by glaciologist Robert Bingham of the University of Aberdeen in Scotland, to verify the information from NASA satellites showing of significant melting of ice in the region.
Researchers were surveyed and the ice cap over nearly 2,500 kilometers, dragging behind them a radar to probe the depths of the crust of ice because the images from NASA photograph that could surface.

"Imagine the Grand Canyon, except that it is a depth of 1.5 km, about 10 km wide and nearly 100 km long," said Robert Bingham told AFP, explaining the discovery of his team.

Based on the observed changes in recent years in West Antarctica, "one can not simply speak of a reduction of the ice sheet as a short-term consequence of global warming," concluded the study. "This is part of a larger system of interactions between tectonic activity, glacial landscape changes and oceanic and atmospheric changes," say the researchers.

Traduced by google

http://www.google.com/hostednews/afp/article/ALeqM5g2XI-CwMUEvsjQJZ...

[Robyn Appleton]

 

 

Meltwater flooding the Watson River in Greenland. Photo taken on July 12, 2012.
CREDIT: NASA Earth Observatory

EDIS Number: FL-20120728-35957-GRL

Event type: Flood

Date/Time: Saturday, 28 July, 2012 at 03:16 (03:16 AM)

Cause of event: Melting ice

Continent: Atlantic Ocean - North

Country: Greenland

County / State: Municipality of Qeqqata

Area: Watson River City: Kangerlussuaq

Coordinate: N 67° 0.517, W 50° 41.350

 

Description Melting ice in Greenland has swelled the island's rivers with water. A NASA satellite snapped a photo of meltwater overflowing the banks of the Watson River near Kangerlussuaq, a key air transportation hub, on July 12. Two weeks later, however, river levels have receded somewhat, according to a release from the NASA Earth Observatory. "Water rises every year, but I've never before observed it at this level of discharge," said Richard Forster, a University of Utah researcher who has done extensive fieldwork in Greenland, in a statement. "It was also about two weeks prior to the normal seasonal peak." The town, known as Kanger, hosts one of the island's busiest commercial airports and is a frequent departure point for scientific research flights. It lies about 74 miles (125 kilometers) from the sea. The water most likely came from melting of the ice sheet - rather than an ice-dammed lake bursting or glacial lake drainage - as the high discharge was maintained for so long, Forster said. The flooding follows reports that 97 percent of Greenland's ice sheets thawed on the surface, according to satellite measurements. Only four days before, just 40 percent of the surface ice layer was thawing.

This year's ice melt is well above average: About half of Greenland's surface ice tends to melt every summer, with the meltwater at higher elevations quickly refreezing in place and the coastal meltwater either pooling on top of the ice or draining into the sea. The massive melt may have been caused by a ridge or dome of warm air hovering over Greenland. Signs of ice melt were even found around Summit Station in central Greenland, which at 2 miles (3.2 kilometers) above sea level is near to the highest point on the ice sheet. The melting characteristics of such a huge ice sheet - spanning 656,000 square miles (1.7 million square kilometers) - is important for various reasons, particularly its potential effect on sea levels. If melted completely, the Greenland ice sheet could contribute 23 feet (7 meters) to global sea-level rise, according to a 2007 report by the Intergovernmental Panel on Climate Change, the international body charged with assessing climate change. Whether or not this recent massive melt will affect the overall ice loss this summer, and as such bump up sea level, is still an open question. In other Greenland-melting news, a massive iceberg that recently broke away from one of Greenland's largest glaciers is making its way downstream and toward the open ocean, as shown by a new satellite photo. The drifting island of ice split from the Petermann Glacier's ice shelf - the front end of a glacier, which hangs off the land and floats on the ocean. Thenewly birthed berg is estimated to be about 46 square miles (120 square kilometers), and finally broke away from the floating tongue of ice on Monday, July 16.

[Howard]

Dramatic video of "iceberg tsunami" resulting from massive collapse of melting ice in Greenland (posted July 19).

[Kojima]

Sea Ice Retreat in the Beaufort Sea [Earth Observatory: July 8, 2012]

As the summer solstice approaches in the Northern Hemisphere, long hours of sunlight warm the Arctic and melt snow and sea ice. Sea ice retreat in June is typical, but the first half of June 2012 brought unusually rapid ice loss, the National Snow and Ice Data Center (NSIDC) reported on June 19.

One area of rapid ice retreat was the Beaufort Sea, north of Alaska. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite collected these images on May 13, 2012 (top), and June 16, 2012 (bottom). By mid-June, the open-water area off the coast had expanded substantially and snow had melted on land.

The rapid melt north of Alaska was part of a larger phenomenon. Sea ice across the entire Arctic reached record-low levels for this time of year, NSIDC stated, slightly below the previous record set in June 2010. It was also lower than the extent in June 2007; Arctic sea ice reached its lowest extent ever recorded by satellite in September 2007.

In the first half of June 2012, the Beaufort Sea was a “hotspot” of rapid retreat, driven by a high-pressure pattern over the region that kept skies clear at the very time of year when sunlight lasts the longest. In addition, larger-scale climate patterns in early June 2012 favored ice retreat along the coastlines of Alaska and Siberia. As of June 18, temperatures were above freezing over much of the sea ice in the Arctic, and snow had melted earlier than normal, leading to warming on land.

On June 19, 2012, NSIDC reported: “Recent ice loss rates have been 100,000 to 150,000 square kilometers (38,600 to 57,900 square miles) per day, which is more than double the climatological rate.” (For comparison, the area of the state of Illinois is roughly 150,000 square kilometers.)

The early onset of the spring melt and the sunny skies around the solstice increased the likelihood of heightened melt rates throughout the rest of the summer, largely by reducing albedo: the proportion of solar energy reflected back into space. If an object reflects all the energy it receives, it has an albedo of 1.0. Sea ice has high albedo because of its bright appearance. But when it starts to melt, its albedo drops from roughly 0.9 to 0.7, causing the ice to absorb more energy. Increased energy absorption leads to increased melt, which exposes ocean water. Thanks to its dark appearance, ocean water has an albedo of less than 0.1. Long, sunny days pour energy into the water, and it retains the heat throughout the summer. In September, when the Sun is low on the horizon, the heated ocean water continues melting sea ice.

[Kojima]

Satellites Observe Widespread Melting Event on Greenland [NASA Earth Observatory: July 12, 2012]

Nearly the entire ice sheet covering Greenland—from its thin coastal edges to its two-mile-thick center—experienced some degree of melting for several days in July 2012. According to measurements from three satellites and an analysis by NASA and university scientists, an estimated 97 percent of the top layer of the ice sheet had thawed at some point in mid-July, the largest extent of surface melting observed in three decades of satellite observations.

The data visualization above shows the extent of surface melting in Greenland on July 8 (left) and July 12, 2012 (right). The maps are based on observations from the Special Sensor Microwave Imager/Sounder (SSMI/S) on the U.S. Air Force’s DMSP satellite, from India’s OceanSat-2, and from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra and Aqua satellites. The satellites measure different physical properties at different scales, and they pass over Greenland at different times. Taken together, they provide a picture of an extreme melt event.

On July 8, satellites showed that about 40 percent of the ice sheet had undergone thawing at or near the surface. By July 12, the extent of melting spread dramatically beyond the norm. In the images above, areas classified as “probable melt” (light pink) correspond to sites where at least one satellite detected surface melting. Areas classified as “melt” (dark pink) correspond to sites where two or three satellites detected melting.

Every summer, a fraction of the surface of the Greenland ice sheet naturally melts. At high elevations, most melt water quickly refreezes in place. Near the coast, some of the melt is retained by the ice sheet and the rest is lost to the ocean.

In mid-July 2012, Son Nghiem of NASA’s Jet Propulsion Laboratory was analyzing radar data from the Indian Space Research Organisation’s Oceansat-2 satellite when he noticed that most of Greenland appeared to have undergone surface melting on July 12. “This was so extraordinary that at first I questioned the result,” said Nghiem. “Was this real or was it due to a data error?”

Nghiem consulted with Dorothy Hall, who studies the surface temperature of Greenland from NASA’s Goddard Space Flight Center. She confirmed that MODIS showed unusually high temperatures over the ice sheet surface and that melt was extensive. Colleagues Thomas Mote of the University of Georgia and Marco Tedesco of the City University of New York also confirmed the melt with passive-microwave data from the DMSP.

The extreme melting coincided with an unusually strong ridge of warm air—a “heat dome”—over Greenland. The ridge was one in a series that dominated Greenland’s weather between May and July 2012.

Even the area around Summit Station in central Greenland, which at two miles above sea level is near the highest point of the ice sheet, showed signs of melting. A National Oceanic and Atmospheric Administration weather station at Summit confirmed that air temperatures hovered above or within a degree of freezing for several hours from July 11 to July 12.

Such pronounced melting at Summit and across the ice sheet has not occurred since 1889, according to ice cores analyzed by Kaitlin Keegan at Dartmouth College. “Ice cores from Summit show that melting events of this type occur about once every 150 years,” said Lora Koenig, a NASA scientist and member of the team analyzing the satellite data. “With the last one happening in 1889, this event is right on time. But if we continue to observe melting events like this in upcoming years, it will be worrisome.”

“The Greenland ice sheet is a vast area with a varied history of change,” said Tom Wagner, NASA’s cryosphere program manager. “This event, combined with other natural but uncommon phenomena such as the large calving event earlier this week on Petermann Glacier, are part of a complex story.”

NASA Earth Observatory images created by Jesse Allen, using data provided by Nicolo DiGirolamo (SSAI) and Dorothy Hall (NASA/GSFC) in the NASA/GSFC Cryospheric Sciences Laboratory. Caption by Maria-Jose Vinas and Mike Carlowicz.

Instrument: Terra - MODIS