The icemelt on Greenland surface has been pretty close to median

and we know iceloss at sealevel was pretty heavy this year.

See the average figure for Greenland iceloss? 281 Gtons wasn’t it?

It retreated in 20 years as much as it had retreated in the previous 100 years.

Grendel wrote on Aug 24^th, 2017 at 2:44pm:

If you were to actually look at the graphs you will see you are wrong.

Have a look and if you can’t work out where you are wrong then I will explain it if you ask nicely. It does not even involve the huge losses of ice at sea level.

Once upon a time, crossing the Arctic was the ultimate challenge. From Franklin to Peary, the Arctic didn’t make it easy, and not every expedition was successful. Now, a Russian tanker has sailed through the usually icy waters without any kind of ice breaker for the first time ever. A success for shipping routes, surely, but a worrying example of climate change too.

The tanker crossed from Norway to South Korea in just 19 days, 30 percent faster than taking the usual route through the Suez Canal, traversing the Russian Arctic section of the route in just six and a half days.

. . . .

Usually, the only way to sail through the Arctic is with the aid of an icebreaker, but the tanker is specially designed to take advantage of the melting sea ice by having an inbuilt one that allowed it to get through ice around 1.2 meters (4 feet) thick without an escort.

. . . .

While the record-breaking travel time can be attributed to the tanker’s new technology, the record low sea ice also made it possible. We know that ice is melting in the Arctic twice as fast as anywhere else and there are obvious fears that increased traffic will damage the fragile ecosystem.

According to Spears, the ship does have green credentials. It can run on the natural gas it’s carrying, which reduces its sulphur oxide emissions by 90 percent and nitrous oxide emissions by 80 percent.

But the fact ships are now being designed in anticipation of less sea ice – you have to be pretty confident to spend $300 million on a new ship design – doesn’t bode well for the future of the Arctic.

Now, a Russian tanker has sailed through the usually icy waters without any kind of ice breaker for the first time ever

Jakobshavn glacier, responsible for feeding flotillas of icebergs into the Ilulissat icefjord — and possibly for unleashing the iceberg that sank the Titanic — is an enormous outlet for the larger Greenland ice sheet, which itself contains enough ice to raise seas by more than 20 feet.

Of that ice, more than 6 percent flows toward the ocean through Jakobshavn, which has raced inland since the 1990s, pouring ever more of its mass into the seas — a change that scientists believe has been caused by warming ocean temperatures. If all of the ice that flows through this region were to melt, it would raise global sea levels by nearly two feet. Just from 2000 to 2011, the ice loss through Jakobshavn alone caused the global sea level to rise by a millimeter.

The U.S. east coast in particular is already a “hot spot” for sea level rise, with rates in many areas exceeding the current global average of a little over 3 millimeters per year.

But until now, researchers have not been sure how far Jakobshavn’s ice extends below sea level — or how much deeper it gets further inland. That’s crucial because Jakobshavn is undergoing a dangerous “marine ice sheet instability,” in which oceanfront glaciers that grow deeper further inland are prone to unstoppable retreat down what scientists call a “retrograde” slope.

That’s where the new science comes in: Researchers who flew over Jakobshavn in a helicopter toting a gravimeter, used to detect the gravitational pull of the ice and deduce its mass, say they’ve found the glacier extends even deeper below sea level than previously realized, a configuration that sets the stage for further retreat.

“The way the bed looks, sort of makes it more prone to continuous retreat for decades to come,” said one of the study’s authors, Eric Rignot, a researcher with NASA’s Jet Propulsion Laboratory and the University of California-Irvine.

Rignot conducted the research with colleagues from his own institution, New York University, the University of Kansas, and Sander Geophysics, which makes the gravimeter used in the study. The study was led by Lu An of the University of California-Irvine, and published in Geophysical Research Letters.

The study found that Jakobshavn is close to 0.7 miles thick where it currently touches the ocean (with only a little over a football field of ice rising above the water and the rest submerged). However, only about five to 10 miles inland toward the center of Greenland, the glacier grows considerably thicker and plunges deeper below sea level, eventually becoming over a mile thick, with nearly a mile of that mass extending below the sea surface. Moreover, the glacier is deep over a vast area.

Along most of that distance, the ice will get steadily deeper and thicker, favoring faster retreat. The glacier front is currently moving backward at about a third of a mile per year, and so will plunge into these deeper regions over the course of coming decades.

The greater depth of Jakobshavn matters for at least two reasons. As it retreats, Jakobshavn will present a thicker ice front to the warm ocean, leading to even greater ice flow and loss. Meanwhile, the depth itself favors increased ice loss because at the extreme pressures involved, the freezing point of ice itself actually changes, making it more susceptible to melting by relatively warm seawater in the deepest part of the fjord.

The deep passageway below Jakobshavn also underscores that, like another enormous Greenland glacier (the far northern Petermann glacier), this outlet connects with a vast and submerged system of canyons that deeply undercut Greenland and travel to its center beneath the ice sheet.

“It’s a direct conduit to the heart of Greenland,” Rignot said. (For a NASA video showing the two vast canyons beneath Greenland’s ice, one connected to Jakobshavn and one to Petermann, see here.)

A few simple calculations help underscore why a further retreat — and accompanying thickening — of Jakobshavn glacier could be such a problem.

Greenland is the world’s largest contributor to sea level rise — according to NASA, it is contributing 281 billion tons of ice to the ocean every year, nearly enough to cause 1 millimeter of sea level rise annually. (It takes 360 billion tons to do that.) That’s from all the various Greenland glaciers and from general melting of the ice sheet that then runs off into the ocean — but Jakobshavn is the single biggest ice loser.