The troubling news continues this week for the Antarctic peninsula region, which juts out from the icy continent.
Last week, scientists documented threats to the Larsen C and the remainder of the Larsen B ice shelf (most of which collapsed in 2002). The remnant of Larsen B, NASA researchers said, may not last past 2020. And as for Larsen C, the Scotland-sized ice shelf could also be at potentially “imminent risk” due to a rift across its mass that is growing in size (though it appears more stable than the remainder of Larsen B).
And the staccato of May melt news isn’t over, it seems. Thursday in Science, researchers from the University of Bristol in Britain, along with researchers from Germany, France and the Netherlands, reported on the retreat of a suite of glaciers farther south from Larsen B and C along the Bellingshausen Sea, in a region known as the Southern Antarctic Peninsula. (For a helpful map of the region, see here.)
Using satellite based and gravity measurements, the research team found that “a major portion of the region has, since 2009, destabilized” and accounts for “a major fraction of Antarctica’s contribution to rising sea level.”
The likely cause of the change, they say, is warmer waters reaching the base of mostly submerged ice shelves that hold back larger glaciers — melting them from below.
This has been a common theme in Antarctica recently — a similar mechanism has been postulated for melting of ice shelves in nearby West Antarctica (which contains vastly more ice, and more potential sea level rise, than does the Antarctic peninsula).
“This is one of now three really quite substantial signals that we’ve seen from different parts of West Antarctica and the Antarctic peninsula that is all going in the same way,” said Jonathan Bamber of the University of Bristol, one of the paper’s authors. The other two are the losses of ice in the Larsen ice shelf region — where glaciers have sped up their seaward lurches following past ice shelf collapses — and in West Antarctica.
What’s particularly notable about the new study is the apparent rapid onset of the change. The researchers say the region is now losing on the order of 56 gigatons of ice per year — a gigaton is a billion metric tons — and that there appears to have been “a remarkable rate of acceleration in dynamic mass loss since about 2009 that must have been near-simultaneous across multiple basins and glaciers.”
Indeed, the paper suggests these southern Antarctic peninsula glaciers may have only begun their retreat. The glaciers may now be unstable, says the paper, because some of their ice shelves currently rest on bedrock that is not only below sea level, but slopes further downhill as one moves inland.
To understand the problem here, it’s important to visualize what scientists call the ice shelf’s “grounding line” – the area where the ice mass simultaneously intersects with the bedrock below it and also the ocean in front of it. “The geometry of the bedrock … it’s below sea level and it dips inland” in this region, explains Bamber. “That geometry means that the grounding line is potentially unstable.”
“It only needs to change position slightly for it to move quite rapidly, and for a sustained period, further inland,” Bamber continues. “That’s the theory behind the instability of these sectors of West Antarctica and the peninsula.”
That’s also one reason why the paper concludes that “these processes have resulted in the destabilization of the inland ice, resulting in a large and sustained mass loss to the ocean.”
So how much sea level rise could be in store – and how fast?
The paper concludes that currently, this part of Antarctica is contributing around .16 millimeters to sea level rise each year, out of a global total that has been recently estimated at about 2.6 to 2.9 millimeters annually. However, in terms of Antarctica’s contribution to the total, .16 millimeters is quite a lot; the new study calls it “a major fraction of Antarctica’s total oceanic contribution.”
The total sea level rise each year is made up of contributions not only from Antarctica, but also from Greenland, polar ice around the world, and also the thermal expansion of sea water (as water warms, its volume increases).
According to Jonathan Bamber, the region contains the potential for a significant contribution to sea level rise – on the order of 20 centimeters for a loss of the entire sector’s ice. This would not unfold immediately – it would play out over “multiple decades to centuries,” he says. But it could contribute meaningfully to total sea level rise in this century.
The greater Antarctic worry remains the ice shelves and glaciers in other regions, West Antarctica and East Antarctica, whose potential contribution to sea level rise is measured in feet or meters, not centimeters or inches. Still, the broad picture is that we’re now seeing consistent — and worrying — changes in many different regions on the fringes of the vast frozen continent.
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