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The coldest and highest parts of the Greenland ice sheet, which in many places is nearly two miles above sea level, are warming rapidly, showing changes unprecedented in at least a millennium, scientists reported Wednesday.
That’s the result of research that extracted several 100-foot or longer ice cores from the world’s second-largest ice sheet. The samples allowed the researchers to construct a new temperature record based on the oxygen bubbles stored in it, which reflect the temperatures at the time the ice was originally deposited.
“We consider the decade from 2001 to 2011 to be the warmest of the entire 1,000-year period,” says Maria Hörhold, first author of the study and scientist at the Alfred Wegener Institute in Bremerhaven.
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And since warming has only continued since that time, the finding is likely an underestimate of climate the high-altitude areas of North and Central Greenland have changed. This is bad news for the planet’s coasts, as it suggests that a long-term melting process is being initiated that could eventually dump a significant, albeit elusive, fraction of Greenland’s total mass into the oceans. Overall, Greenland contains enough ice to raise sea levels by more than 20 feet.
The study linked temperature records uncovered by ice cores from 2011 and 2012 with records from older and longer cores reflecting temperatures over the ice sheet a millennium ago. The youngest ice contained in these older cores was from 1995, meaning they can’t tell much about today’s temperatures.
The work also found that this part of Greenland, the vast north-central region, is now 1.5 degrees Celsius (2.7 degrees Fahrenheit) warmer compared to the entire 20th century and that the rate of melting and water loss from the ice has increased Leaf – which raises sea levels – has been increasing in tandem with these changes.
The research results were published Wednesday in the journal Nature by Hörhold and a group of researchers from the Alfred Wegener Institute, the Neils Bohr Institute in Denmark and the University of Bremen in Germany.
The new research “pushes the instrument record back by 1,000 years using data from Greenland showing unprecedented warming in recent times,” said Isabella Velicogna, a glaciologist at the University of California, Irvine, who is not affiliated with the research was.
“This doesn’t change what we already knew about the warming signal in Greenland, the increase in melt and the accelerated flow of ice into the ocean, and that it will be difficult to slow it down,” Velicogna said. “Nevertheless, it adds momentum to the seriousness of the situation. This is bad, bad news for Greenland and for all of us.”
Scientists have postulated that if the air over Greenland got warm enough, a feedback loop would emerge: melting the ice sheet would cause it to descend to a lower altitude, which would naturally expose it to warmer air, leading to more melting and sagging would lead. and so forth.
However, that this north-central part of Greenland is now 1.5 degrees Celsius warmer than it was in the 1900s does not necessarily mean that the ice sheet has reached that feared ‘tipping point’.
Recent research has found that Greenland’s dangerous threshold is around 1.5 degrees Celsius or more of planetary warming – but that’s a different figure than regional ice sheet warming. If the globe warms by an average of 1.5°C, which could happen as early as the 2030s, Greenland’s warming is likely to be even higher — and higher than it is now.
Researchers consulted by the Washington Post also stressed that the northern region of Greenland, where these temperatures were recorded, is known for other reasons to have the potential to trigger a large sea-level rise.
“We should be concerned about North Greenland’s warming, because in that region there are a dozen sleeping giants in the form of broad tidewater glaciers and an ice stream…waking up will increase the contribution to Greenland’s sea level,” said Jason Box, a scientist at the Geological Survey of Denmark and Greenland.
Box published a study last year that suggests Greenland is already doomed to lose in the current climate an amount of ice equivalent to almost a foot of sea level rise. This projected sea level rise will only get worse as temperatures continue to warm.
The concern centers on the Northeast Greenland ice flow, which is channeling a large portion – 12 percent – of the ice sheet towards the sea. It is essentially a massive, slow-moving river that ends in several very large glaciers that empty into the Greenland Sea. It’s already thinning, and the glaciers at its terminus have lost mass—one of them, Zachariae Isstrom, has also lost its frozen shelf that once stretched across the ocean.
Recent research has also shown that during past warm periods of relatively recent Earth history (i.e. the last 50,000 years or so) this part of Greenland often contained less ice than it does today. In other words, the ice flow could extend further outward from central Greenland than can be sustained at current temperatures, and be has a strong tendency to move backwards and give up a lot of ice.
“Paleoclimate and modeling studies suggest that northeast Greenland is particularly vulnerable to global warming,” said Beata Csatho, an ice sheet expert at the University of Buffalo.
The same year that researchers were drilling the ice cores on which the current work is based – 2012 – something remarkable happened in Greenland. That summer, in July, surface melting conditions occurred over much of the ice sheet, including in the cold and very high locations where the research was conducted.
“It was the first year in which one observed that one melts in these elevations,” said Hörhold. “And now it goes on.”
correction
An earlier version of this article stated that the Neils Bohr Institute was in Germany. It’s in Denmark.