NASA scientists say that in July, Greenland's surface ice cover melted over a more extensive area than at any time in more than 30 years of satellite observation. Measurements show that Greenland ice cover has experienced unprecedented degree of melting.
According to NASA, half of the surface of Greenland's ice sheet normally melts in summer with most of the melt water refreezing at high elevations. At the coast, some of melt water is retained by ice sheet with the rest lost to the ocean.
This year, however, ice melting has been more extensive than in recent years. Satellite data shows an estimated 97 percent of the ice sheet surface thawed in mid-July. Melt maps from three independent satellites showed that the melting spread quickly. On July 8 about 40 percent of the ice sheet's surface had melted and by July 12, 97 percent had melted.
Researchers are not certain whether the extensive melt will affect the overall volume of ice loss and contribute to sea level rise.
According to NASA, on July 12, Son Nghiem of NASA's Jet propulsion Laboratory in Pasadena California, looking at data from the Indian Space Research Organization's (ISRO) Oceansat-2 sateliite, noticed that most of Greenland had undergone surface melting. 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 Dorothy Hall, who studies the surface temperature of Greenland at NASA's Goddard Space Flight Center in Green belt, Md. Hall confirmed that the Moderate-resolution Imaging Spectroradiometer (MODIS) showed unusually high temperatures and that the 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 Ocean-2 and MODIS, using passive-microwave satellite data from the Special Sensor Microwave Imager/Sounder on a U.S. Air Force meteorological satellite.
The event, according to NASA, coincided with a period of unusually strong warm air, or heat dome, over Greenland. The ridge of warm air was one of a series that featured strongly in Greenland's weather since the end of May.
NASA says that even the area around Summit Station in central Greenland which is 2 miles above sea level showed signs of melting that has not been seen since 1889.
The BBC reports NASA chief scientist, Waleed Abdalati, said: "When we see melt in places that we haven't seen before, at least in a long period of time, it makes you sit up and ask what's happening. It's a big signal, the meaning of which we're going to sort out for years to come."
He said that because this is not the first time this has happened, scientists are uncertain whether it is natural or if it is caused by man-made climate change.
The Guardian reports that Jay Zwally, glaciologist at NASA's Goddard Space Flight Center, said he had made almost yearly trips to the Greenland ice sheet for more than three decades, but he had never observed such a rapid melt. According to Zwally, although he and his colleagues have been recording an acceleration of the melting in the last few decades, this year's melting has been dramatic. He said his team had to rebuild their camp at Swiss Station after the snow and ice supports melted.
Zwally said he was surprised to see evidence in the images of melting around the area of Summit Station. He said: "If you look at the 8 July image that might be the maximum extent of warming you would see in the summer. 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."
According to The Guardian, the consequence of melting of Greenland ice is further sea level rise and warming of the Arctic. Scientists estimate that about one-fifth of the annual sea level rise of 3mm, is due to the melting of the Greenland ice sheet.
The Huffington Post reports that NASA's cryosphere program manager, Tom Wagner, said that although this melting may be part of a natural variation, "We have abundant evidence that Greenland is losing ice, probably because of global warming, and it's significantly contributing to sea level rise."
Over the past few months, separate studies suggest humans are playing a role in ocean warming, and that specific regions of the world, such as the U.S. East Coast, are increasingly vulnerable to sea level rise.
According to Wagner, Greenland's overall ice mass is changing and he believes this is due mostly to warmer ocean waters "eating away at the ice." He said, "It seems likely that's correlated with anthropogenic warming."
Lora Koenig, a Goddard glaciologist and member of the research team analyzing the satellite data, said, "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. But if we continue to observe melting events like this in upcoming years, it will be worrisome."