An Iceberg the Size of Delaware Breaks Off in Antarctica

#LarsenC break-up extends the march of ice shelf retreat toward the pole, as climatic limit recedes to the south [UPDATED with latest break] pic.twitter.com/JdX97nsw2h

— Climate Signals (@ClimateSignals) July 12, 2017

by Gaius Publius

We need new Cassandras to warn us of new disasters, even though they'll never be believed.

—Richard Clarke (paraphrased)

I'll be your Cassandra this week.

—Yours truly

Part of a massive ice shelf in Antarctica, called "Larsen C," has split, and a huge iceberg has "calved off" from the rest of the glacier and entered the ocean. See the tweeted image above (original tweet with full-sized image here). The iceberg really is almost the size of Delaware.

As you can see, the ice shelves labeled Larsen A and Larsen B are gone. Larsen C, further toward the South Pole is collapsing next. (Ice shelves are glacial ice laying in and over the water.) Notice the southward move, from the upper (warmer, more northern) tip of the peninsula toward the southern (cooler) mass of the continent itself.

This is quite dramatic, and while "calving" of ice shelves occurs naturally, the southward move of this sequence is highly suggestive of the march of global climate change. (That's careful-scientist talk, as you'll read below. The person who is certain the globe is drastically changing, on the other hand — meaning almost everyone in the country who has no power — gets it that Antarctica is doomed to melt.)

Here's one report, from ClimateSignals.org:

Larsen C Ice Shelf Calving and Retreat 2017

Short Summary

The imminent calving and the potential follow-on long-term retreat of Antarctica's Larsen C ice shelf extend a southward march of ice shelf breakup down the Antarctic Peninsula toward the South Pole, a progression consistent with the direction of climate change and dramatic warming on the Peninsula since the 1950s.

The Antarctic Peninsula exhibits an extraordinarily large range of natural variation. And the immediate mechanisms driving the current calving of Larsen C are understood as part of the ongoing natural process of ice calving along the Antarctic Peninsula. However, key questions about the break remain unanswered, hampered in part by the lack of direct observations.

Larsen C has retreated significantly since the 1980s. And once the rapidly advancing crack in the continent’s fourth-largest ice shelf makes its final cut, the extent of Larsen C will be the smallest on record, probably the smallest since the last interglacial period 115,000 years ago. While the size of the current breakaway is not unprecedented in recent decades, the calving will create one of the largest icebergs on record.

The remaining ice shelf is projected to be unstable and may be prone to runaway collapse over the coming years, an event witnessed in the recent collapses of the Larsen A and Larsen B ice shelves. There is significant evidence that various mechanisms driven by climate change may be weakening the Larsen C ice shelf, increasing its vulnerability to forces pushing the shelf toward retreat, and in the longer term, potentially eventual collapse.

The loss of the Larsen C ice shelf won't significantly affect sea level. The loss of ice shelves doesn't raise sea levels. A collapse of Larsen C could allow blocked glaciers to flow toward the ocean, eventually contributing roughly 1 centimeter to sea level rise.

For context, here's a map of that part of Antarctica showing the ice shelves and the underlying land mass:

Note that Larsen A and Larsen B ice shelves are indeed gone, calved off completely.

More from ClimateSignals.org (my emphasis):

Larsen C ice shelf: At the cross roads

The collapse of several ice shelves in sequence going down the eastern side of the Antarctic Peninsula (AP) occurred after decades of observed surface warming. And the direction of the breakup has progressed poleward toward the largest AP ice shelf, Larsen C, suggesting a southerly migration of the climatic limit for ice shelves on the AP.[2][1]

Some of these losses are unusual over the last 10,000 years and have been widely attributed to atmospheric and oceanic changes. As of 2010, 18% of the overall ice shelf area on the AP had been lost, roughly 11,000 square miles.[2] After the current calving event is complete, the extent of Larsen C will be the smallest on record[6] and probably the smallest since the last interglacial period 115,000 years ago.[5]

Larsen now straddles the temperature line considered as the practical limit for the viability of ice shelves in the Antarctic.[1]

The "last interglacial period" (called the Eemian) was the warming period prior to the most recent ice age. At its height, the Eemian had temperatures either about the same as temperatures are today (i.e., after the rapid recent temperature rise of the last 150 years) or about one degree Celsius warmer.

What does that mean for us? An earlier ThinkProgress piece by Joe Romm explains:

Right now, we’re headed towards an ice-free planet. That takes us through the Eemian interglacial period of about 130,000 years ago when sea levels were 15 to 20 feet higher, when temperatures had been thought to be about 1°C warmer than today. Then we go back to the “early Pliocene, when sea level was about 25 m [82 feet] higher than today,” as NASA’s James Hansen and Makiko Sato explain in a new draft paper, “Paleoclimate Implications for Human-Made Climate Change.”

Pause at this point. At the peak of the Eemian, temperatures were no more than one degree higher than today, and "sea levels were 15 to 20 feet higher."

That's where we're headed and beyond, all to keep David Koch, Rex Tillerson and every other libertarian billionaire megalomaniac ("I just want to win till I die; is that too much to ask?") in the pathological winner's circle. Not a fair trade, you might think.

More on that winner's circle — and that pathology — in a bit. For now, just bringing the news. Antarctica has started to melt in front of us.

GP