text: The Greenland ice sheet melted at a faster rate this month than at any other time in recorded history, with virtually the entire ice sheet showing signs of thaw. 
   
   The rapid melting over just four days was captured by three satellites. It has stunned and alarmed scientists, and deepened fears about the pace and future consequences of climate change. 
   
   In a statement posted on Nasa's website on Tuesday, scientists admitted the satellite data was so striking they thought at first there had to be a mistake. 
   
   "This was so extraordinary that at first I questioned the result: was this real or was it due to a data error?" Son Nghiem of Nasa's Jet Propulsion Laboratory in Pasadena said in the release. 
   
   He consulted with several colleagues, who confirmed his findings. Dorothy Hall, who studies the surface temperature of Greenland at Nasa's space flight centre in Greenbelt, Maryland, confirmed that the area experienced unusually high temperatures in mid-July, and that there was widespread melting over the surface of the ice sheet. 
   
   Climatologists Thomas Mote, at the University of Georgia, and Marco Tedesco, of the City University of New York, also confirmed the melt recorded by the satellites. 
   
   However, scientists were still coming to grips with the shocking images on Tuesday. "I think it's fair to say that this is unprecedented," Jay Zwally, a glaciologist at Nasa's Goddard Space Flight Center, told the Guardian. 
   
   The set of images released by Nasa on Tuesday show a rapid thaw between 8 July and 12 July. Within that four-day period, measurements from three satellites showed a swift expansion of the area of melting ice, from about 40% of the ice sheet surface to 97%. 
   
   Scientists attributed the sudden melt to a heat dome, or a burst of 
   
   unusually warm air, which hovered over Greenland from 8 July until 16 
   
   July. 
   
   Greenland had returned to more typical summer conditions by 21 or 
   
   22 July, Mote told the Guardian. 
   
   But he said the event, while exceptional, should be viewed alongside 
   
   other compelling evidence of climate change, including on the ground 
   
   in Greenland. 
   
   "What we are seeing at the highest elevations may be a sort of sign of 
   
   what is going on across the ice sheet," he said. "At lower elevations 
   
   on the ice sheet, we are seeing earlier melting, melting later in the 
   
   season, and more frequent melting over the last 30 years and that is 
   
   consistent of what you would expect with a warming climate." 
   
   Zwally, who has made almost yearly trips to the Greenland ice sheet for more than three decades, said he had never seen such a rapid melt. 
   
   About half of Greenland's surface ice sheet melts during a typical summer, but Zwally said he and other scientists had been recording an acceleration of that melting process over the last few decades. This year his team had to rebuild their camp, at Swiss Station, when the snow and ice supports melted. 
   
   He said he had never seen such a rapid melt over his three decades of 
   
   nearly yearly trips to the Greenland ice sheet. He was most surprised 
   
   to see indications in the images of melting even around the area of 
   
   Summit Station, which is about two miles above sea level. 
   
   It was the second unusual event in Greenland in a matter of days, after an iceberg the size of Manhattan broke off from the Petermann glacier. But the rapid melt was viewed as more serious. 
   
   "If you look at the 8 July image that might be the maximum extent of warming you would see in the summer," Zwally noted. "There have been periods when melting might have occurred at higher elevations briefly – maybe for a day or so – but to have it cover the whole of Greenland like this is unknown, certainly in the time of satellite records." 
   
   Jason Box, a glaciologist at Ohio State University who returned on 
   
   Tuesday from a research trip to Greenland, had been predicting a big 
   
   melt year for 2012, because of earlier melt and a decline in summer 
   
   snow flurries. 
   
   He said the heat dome was not necessarily a one-off. "This is now the 
   
   seventh summer in a row with this pattern of warm air being lifted up 
   
   onto the ice sheet on the summer months," he said. "What is surprising 
   
   is just how persistent this circulation anomaly is. Here it is back 
   
   again for the seventh year in a row in the summer bringing hot, warm 
   
   air onto the ice sheet." 
   
   He also said surfaces at higher elevation, now re-frozen, could be 
   
   more prone to future melting, because of changes in the structure of 
   
   the snow crystals. Box expected melting to continue at lower 
   
   elevations. 
   
   About half of Greenland's surface ice sheet melts during a typical 
   
   summer, but Zwally said he and other scientists had been recording an 
   
   acceleration of that melting process over the past few decades. This 
   
   year his team had to rebuild their camp, at Swiss Station, when the 
   
   snow and ice supports melted. 
   
   
   
   Lora Koenig, another Goddard glaciologist, told Nasa similar rapid melting occurs about every 150 years. But she warned there were wide-ranging potential implications from this year's thaw. 
   
   "If we continue to observe melting events like this in upcoming years, it will be worrisome." she told Nasa. 
   
   The most immediate consequences are sea level rise and a further warming of the Arctic. In the centre of Greenland, the ice remains up to 3,000 metres deep. On the edges, however, the ice is much, much thinner and has been melting into the sea. 
   
   The melting ice sheet is a significant factor in sea level rise. Scientists attribute about one-fifth of the annual sea level rise, which is about 3mm every year, to the melting of the Greenland ice sheet. 
   
   In this instance of this month's extreme melting, Mote said there was evidence of a heat dome over Greenland: or an unusually strong ridge of warm air. 
   
   The dome is believed to have moved over Greenland on 8 July, lingering until 16 July. ||||| Greenland's Petermann Glacier birthed a massive new iceberg in June 2012. The glacier has shrunk significantly in recent years. 
   
   Greenland ice, it seems, can vanish in a flash, with new satellite images showing that over just a few days this month nearly all of the veneer of surface ice atop the island's massive ice sheet had thawed. 
   
   That's a record for the largest area of surface melt on Greenland in more than 30 years of satellite observations, according to NASA and university scientists. 
   
   The images, snapped by three satellites, showed that about 40 percent of the ice sheet had thawed at or near the surface on July 8; just days later, on July 12, images showed a dramatic increase in melting with thawing across 97 percent of the ice sheet surface. 
   
   "This was so extraordinary that at first I questioned the result: was this real or was it due to a data error?" said Son Nghiem of NASA's Jet Propulsion Laboratory in Pasadena, Calif., referring to the July 12 images taken by the Indian Space Research Organisation's (ISRO) Oceansat-2 satellite. 
   
   Extent of surface melt over Greenland’s ice sheet on July 8 (left) and July 12 (right) based on data from three satellites. (Light pink: probable melt, meaning at least one satellite showed melt; dark pink: melt, meaning two to three satellites showed melt. Credit: Nicolo E. DiGirolamo, SSAI/NASA GSFC, and Jesse Allen, NASA Earth Observatory 
   
   Nghiem had reason to be baffled, as this record 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. [Giant Ice: Photos of Greenland's Glaciers] 
   
   Instruments on two other satellites proved out Nghiem's findings — the Moderate-resolution Imaging Spectroradiometer (MODIS) on NASA's Terra and Aqua satellites 
   
   Data from the Special Sensor Microwave Imager/Sounder on a U.S. Air Force meteorological satellite also confirmed the mind-blowing melt. 
   
   As for what caused the disappearing ice, University of Georgia, Athens climatologist Thomas Mote suggests it could be a ridge or dome of warm air hovering over Greenland that coincided with the extreme melt. 
   
   "Each successive ridge has been stronger than the previous one," Mote said in a NASA statement. The latest in a series of these heat domes, which have dominated Greenland weather since May, began to move over Greenland on July 8, before coming to a halt over the ice sheet some three days later. By July 16, the heat dome had started to dissipate. 
   
   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 of the ice sheet. 
   
   "Ice cores from Summit show that melting events of this type occur about once every 150 years on average," said study researcher Lora Koenig, a glaciologist at NASA's Goddard Space Flight Center in Greenbelt, Md. "With the last one happening in 1889, this event is right on time," Koenig said in a statement. 
   
   The melting of such a huge ice sheet — spanning an area of 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 (IPCC), 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. 
   
   Scientists say that man-made global warming, a result of greenhouse gas emissions, is contributing to Greenland ice melt. In fact, past research has suggested that the Greenland ice sheet will vanish in 2,000 years under business-as-usual carbon emissions. If humans managed to limit global warming to 3.6 degrees Fahrenheit (2 degrees Celsius), the disappearance would take 50,000 years. 
   
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target: – Greenland isn't just losing Manhattan-sized chunks of ice from its huge glaciers. A heat-dome that moved over Greenland on July 8 caused surface melt to soar from 40% to an unprecedented 97% in just four days, reports Live Science. Typically, just half of Greenland's surface ice melts during the summer. "This was so extraordinary that at first I questioned the result: Was this real or was it due to a data error?" said one researcher. There were even signs of ice melt at Summit Station in central Greenland, a point two miles high and near the thickest part of the ice sheet. "Ice cores from Summit show that melting events of this type occur about once every 150 years on average," said one glaciologist. "With the last one happening in 1889, this event is right on time." However, she cautioned that such a wide-ranging melt was rare and a potential warning. "If we continue to observe melting events like this in upcoming years, it will be worrisome," she told the Guardian.