Trusel said the greatest takeaway from the study is the speed at which Greenland ice is melting, particularly over the last two and a half decades.
“It’s not just increasing, it’s accelerating,” he said. “That’s a key concern for the future.”
To reach these conclusions, Trusel and several of his coauthors explored Greenland in search of the ice sheet’s “Goldilocks zone.” He explained that to get a good record of the ice sheet’s melt history, they needed to find sites that thaw enough each year to capture melt variability and record it as refrozen melt layers, but that do not melt too much where water runs off the ice sheet and leaves no trace preserved in the ice.
“We found those sites and drilled our deepest cores in 2015,” Trusel said. “The real scientific breakthrough was being able to show that the ice cores tell us not just the amount of melt at the sites where we drilled the cores, but also how much melt was happening at the warmer, lower elevations, and running off the ice sheet into the ocean.”
An article in Nature explaining the study’s results described the massive amount of water flowing from the thawing ice:
“(Trusel's) team’s study shows that Greenland’s runoff hit a 350-year high in 2012, when the ice sheet released about 600 gigatonnes of water into the ocean — enough to fill 240 million Olympic swimming pools.”
This first-of-its-kind study determined that increases in Greenland melting coincided with the onset of warming of the Arctic associated with the Industrial Revolution, declining summer Arctic sea ice and slowing of an important ocean current in the North Atlantic that affects climate across the globe. The confluence of these processes demonstrates just how sensitive the polar regions are to climate change, as well as the potentially wide-ranging consequences of Arctic change, said Trusel.
The article also reports that melt intensity found in Greenland ice cores over the past 20 years is roughly 250 to 575 percent greater than it was during the pre-industrial period and that the years 2004-2013 produced the greatest melt of any decade over the past 365 years.
While the article focuses largely on the past four centuries, Trusel said deeper ice cores taken from the Arctic suggest warming such as is now underway has not occurred for as long as 8,000 years.
"The numbers are staggering,” said Trusel, “and part of why it’s melting so fast now is that melting outpaces warming. For every degree Greenland temperatures increase, melting increases exponentially.”
Trusel noted that scientists believe meltwater runoff from the Greenland ice sheet will exacerbate rising sea levels for centuries to come.
Recent observations show that sea level rise is already accelerating, and that Greenland ice is the largest contributor of new water added to the ocean each year. If Greenland’s ice sheet, which is roughly one mile deep and more than twice the size of Texas, were to melt completely, it would raise sea levels worldwide by nearly 23 feet, submerging islands and coastal communities the world over.
“What we do now and in the near-term future is not just critical for the future of the Greenland ice sheet, but for our livelihoods and economies. How much Greenland ice melts, and how fast, is ultimately a function of how much we warm the atmosphere.”
He noted that coastal flooding along the U.S. coastline has increased 5 to 10-fold or more since the 1960s and that flooding, especially during major storms, is predicted to get much worse.
“The increased risk from rising seas pose a particularly acute threat to the New Jersey coast,” he said.
In fact, he said, “sea level rise has been faster along the Jersey Shore than elsewhere because our land is sinking while the ocean is rising.”
Trusel’s research finds common timing between Greenland melting and slowing of the Atlantic Meridional Overturning Circulation, which bring warm water north, where it cools and sinks. According to the most recent U.S. National Climate Assessment 4, slowdown or stoppage of this current due to Greenland melting adding fresh water to the ocean would cause sea level rise to be even greater across the U.S. Northeast.
Trusel said the study adds to a growing body of scientific evidence that demonstrates how impactful human-induced climate change is. Starting with the dawn of the Industrial Revolution and continuing through today, humans have directly contributed to a warming planet, with the effects wide-ranging and unprecedented in recent time.
“Climate change is here, and it’s clear. The evidence is preserved in the ice. What happens next? That’s up to us.”
The Nature article was Trusel's third published paper in as many weeks. On Nov. 12 and 19 he published the articles, “The Greenland and Antarctic ice sheets under 1.5 °C global warming,” and “Antarctic surface hydrology and impacts on ice-sheet mass balance,” in the journal Nature Climate Change, a subsidiary of Nature.
The research project was funded by the U.S. National Science Foundation with support from Rowan University, Woods Hole Oceanographic Institution, the U.S. Department of Defense, the Netherlands Organization for Scientific Research, the Netherlands Earth System Science Center and the Belgian national Fund for Scientific Research.
The research team included Dr. Sarah Das and Matthew Osman, Woods Hole Oceanographic Institution; Dr. Matthew J. Evans, Wheaton College; Dr. Ben E. Smith, University of Washington; Dr. Xavier Fettweis, University of Liège, Belgium; Dr. Joseph R. McConnell, Desert Research Institute, Reno, Nev.; and Dr. Brice P.Y. Nöel and Dr. Michiel R. van den Broeke, Utrecht University, Netherlands.
(Photo gallery above includes images from Sarah Das and Matt Osman, Woods Hole Oceanographic Institution, and Trusel. Main story image courtesy of Das.)