Sudden Greenland ice sheet melt: is this climate change?
Nearly all of Greenland's ice sheet began to melt for a few days in July. Is climate change to blame?
MELTWATER was so sudden and widespread across the Greenland ice sheet earlier this month that scientists thought they must have misread the data.
Over a period of just four days, 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 interior, experienced some degree of melting at its surface," says Nasa. Son Nghiem at the agency's Goddard Jet Propulsion Laboratory said: "This was so extraordinary that at first I questioned the result: was this real or was it due to a data error?"
However, the "extreme melt event" was confirmed by observations from three different satellites.
Data showed that on 8 July about 40 per cent of the surface of the Greenland ice sheet had melted. By 12 July, 97 per cent had thawed.
The news comes a week after Nasa released a photograph of a huge iceberg breaking off from Greenland's Petermann Glacier. Scientists also reported that the Arctic had experienced the largest sea ice loss on record for June.
The series of events has raised fears we are witnessing the effects of global warming.
Nasa glaciologist Jay Zwally told The Guardian that the sudden ice sheet melt was "unprecedented" - and more serious than the Petermann Glacier's massive calving event.
"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."
Karl Braganza of Australia's Bureau of Meteorology is also concerned. "In terms of just one event taken in isolation, you can't tell much from it...But clearly there is a trend going on in the Arctic this century," he told The Age.
"We have warmer ocean temperatures, now what looks like particularly large reductions in sea ice, and large chunks of glaciers breaking off.
"What's alarming to scientists is that we know the Arctic ice is a key feedback, and the warming in the Arctic has been slightly faster than was predicted 10 or 20 years ago."
Dr Braganza notes that levels of CO2 in the Arctic are now at the level they were three million years ago during the Pliocene period. Back then, there was no ice on Greenland.
In its press release about the Greenland melt event, Nasa does not mention 'climate change' or 'global warming'. It puts the widespread thaw down to freak weather. Apparently, a series of "heat domes" - unusually strong ridges of warm air - have dominated Greenland's weather since May.
The agency also points out that although it has never previously been recorded by satellites, melting of this kind happens once every 150 years or so.
Nasa glaciologist Lora Koenig, said: "With the last one happening in 1889, this event is right on time." However, she suggested we ought not get too comfortable: "If we continue to observe melting events like this in upcoming years, it will be worrisome."