A new scientific survey has found that the glaciers of the Arctic are the world's biggest contributors to rising seas, shedding ice at an accelerating rate that now adds well over a millimeter to the level of the ocean every year.
That is considerably more ice melt than Antarctica is contributing, even though the Antarctic contains far more ice. Still, driven by glacier clusters in Alaska, Canada and Russia and the vast ice sheet of Greenland, the fast-warming Arctic is outstripping the entire ice continent to the south - for now.
However, the biggest problem is that both ice regions appear to be accelerating their losses simultaneously - suggesting that we could be in for an even faster rate of sea level rise in future decades. Currently, seas are rising by about 3 millimeters each year, according to NASA. That's mainly driven by the Arctic contribution, the Antarctic, and a third major factor - that ocean water naturally expands as it warms.
For Arctic ice loss, "the rate has tripled since 1986," said Jason Box, first author of the new study and a scientist at the Geological Survey of Denmark and Greenland. "So it clearly shows an acceleration of the sea level contribution."
"Antarctica will probably take over at some point in the future, but during the past 47 years of this study, it's not controversial that the Arctic is the largest contribution of land ice to sea level rise," he said.
Scientists in the U.S., Chile, Canada, Norway and the Netherlands contributed to the work, which was published in Geophysical Research Letters.
The Arctic is also losing floating sea ice at a rapid pace, but that loss does not contribute substantially to rising seas (though it has many other consequences). Sea ice losses closely match what is happening on land, which makes sense since both phenomena are being driven by the fast warming of the atmosphere in the Arctic, which has heated up at a rate much faster than seen in lower latitudes. Warming seas are also driving some of the ice loss.
Here's the new study's tally of where all the Arctic ice loss has come from, since the year 1971:
The research was performed by merging a highly reliable gravity-based measurement of Arctic mass loss from NASA's GRACE satellites with older direct ice measurements, taken from the field, going back to 1971.
The total Arctic loss at present is 447 billion tons of ice per year - which Box calculated is some 14,000 tons of water per second. That's for the period between 2005 and 2015. Between 1986 and 2005, the loss is calculated at around 5,000 tons per second - therefore, the rate has almost tripled.
Separate research has recently found that the Antarctic's loss rate has also tripled in just a decade, reaching 219 billion tons per year from 2012 to 2017.
Assuming these numbers are correct and summing them together, the world's polar regions are losing about 666 billion tons of ice to the ocean each year - amounting to a little bit less than 2 millimeters of sea level rise annually.
Treating the Arctic as a whole can miss something, though, notes Christopher Larsen, a glacier expert at the University of Alaska at Fairbanks.
Namely, the Arctic acceleration documented in the study is really being driven by Greenland, which contains more than 20 feet of potential sea level rise, dwarfing all other Arctic ice sources.
"With respect to the present rate of ice mass loss, and the increasing rates thereof, it is Greenland that has the most significant rate of increased mass loss in the present day," Larsen said in an email.
"This is especially noteworthy as ultimately Greenland has the most ice to lose in the Northern Hemisphere," he said. "As rapid as ice loss is now or may become anywhere in the north, the regional totals of ice mass within Alaska or the Arctic Canada are smaller that what Greenland holds."
To give a sense of the scale of the Arctic losses, Box imagined what it would mean if they were distributed among the Earth's human population.
"If you take the 7.7 billion people on Earth, and divide the present day numbers, from 2005 to 2015, each person on Earth would have the equivalent of 160 liters per day, every day, every year," Box said.