mewo2

There's a big difference between average temperatures and peak temperatures. On Larsen C, we regularly measure localised temperatures in excess of 10˚C for days at a time. That's enough for some serious melt.

Also, surface melt is only half the story. The base of the ice is in contact with the ocean, which is also warming. Water in contact with ice is (more or less by definition) at the freezing/melting point - if it warms, the ice melts a bit, if it cools, the water freezes. So a change in ocean temperatures can have a big effect on melt rates.

Finally, it's not enough that the shelf be in equilibrium, melt-wise. The ice is constantly thinning, as it stretches and flows under its own weight. There needs to be enough extra mass added (mostly as snow) to compensate for that, if the shelf is to remain a constant thickness.

For some context on size, the calving event in this video is about 7 cubic kilometers. The Larsen C berg will be about 1000 cubic kilometers. On the other hand, this berg is overturning, so the calving is, to put it mildly, quite energetic (equivalent to a couple of hundred kilotons of TNT). The Larsen C berg will just drift away in a much less dramatic fashion.

Well, it's a major news story - according to our press office, over a thousand outlets worldwide were carrying the story. So it would be weird if Business Insider didn't cover it. That said, I'm slightly surprised that this is the version of the story linked on HN. Personally, I like the BBC version better: http://www.bbc.co.uk/news/science-environment-38522954

What that bit is referring to is that the ice shelf has been thinning as a result of climate change. The temperatures on the Antarctic Peninsula have increased by about 3˚C (5˚F) over the past half century or so, which is a huge change to the climate of a region.

Unlikely, it's hard for these things to get close to the coast - remember that the base is several hundred meters below sea level, so it will ground if it gets into even remotely shallow water. More likely it'll break up, and bits will wander off into the South Atlantic and Indian oceans.

I think you might need to recalibrate your idea of the scale of this object. The iceberg weighs about a trillion (10^12) tons. For comparison, a Nimitz-class aircraft carrier is about a hundred thousand (10^5) tons. So you're talking about moving an object which weighs about a million times as much as the whole US Navy carrier fleet.

Then, once you had it back into position, you'd need to apply your "glue" to the whole crack surface, which is around 40 square kilometers, a little smaller than Manhattan Island. Also, the majority of that crack surface is hundreds of meters deep in sub-zero waters in one of the most inaccessible places on the planet.

Then, once you've done that, the same forces which caused this bit to calve off would cause a new bit to calve a year or two later.

Yeah, once these things are moving, you don't need much resolution to see them - we're talking about objects several kilometers wide, at the very least. Easily visible on even the most primitive satellite imagery. The difficulties would be cloud cover and orbital inclination.

We need to distinguish between sea ice (a ~1m thick layer of frozen seawater), and land ice (up to 3000m thick layer of compacted snow). Sea ice is quick to respond to climate change (because it's so thin), and has a large seasonal component to its extent. Land ice is much slower to respond, and harder to replace once it's gone.

Antarctic sea ice extent has been increasing, largely because of a change in wind patterns. Winds blow ice away from the coast, leading to more open water, which leads to more sea ice formation. Even though Antarctica is getting warmer, it's still much too cold to melt sea ice in most places, so climate warming isn't having a huge direct effect on sea ice.

However, the land ice in the Antarctic is almost certainly decreasing (exact measurements are quite hard), and the trend is definitely towards more ice loss. Ice shelves, although floating, are the outer extremes of this land ice.

This is a good review paper on the subject of the mass balance of land ice: http://www.vliz.be/imisdocs/publications/248038.pdf

I think there are some microorganisms in the snowpack, but other than that it's a pretty barren place, at least above the water. Below, a lot of sea life congregates around the ice front - there are nutrients that melt out of the ice - and this supports an ecosystem, but that should all just move to the new ice front. The iceberg itself will probably support a small marine ecosystem as it floats away and melts.

I'm not an ecologist though, so I'm hazy on the details.

Yes, the edges are impressive, aren't they? The ice is floating, almost flat, and has had hundreds of years to reach equilibrium, so there's practically zero vertical shear stress in the ice shelf. As well as that, the ice itself is very laterally homogeneous - there are layers within it, but all the horizontal variability is on scales of kilometers or more. There are no particular faults or planes of weakness within the material. This means that when it breaks under tension, like this, it breaks in a very clean and even way.

Also, remember, you're only seeing the top 10% or so of the berg. There can be interesting shapes below the waterline, caused by preferential melting.

As for the glaciers feeding the shelf, that's an interesting question. Floating ice on its own provides very little resistance to their flow, but the mouth of the ice shelf is narrower than the back, so the converging flow has a resistive effect, like squeezing toothpaste out of a tube. If a gap is made in the ice blocking the mouth, then there should be some speedup of the glaciers. It all depends on exactly where the rift goes next, and on the exact balance of stresses in the shelf, which there's some uncertainty about.

It's unlikely in this case, but it has happened in some other areas. The Brunt Ice Shelf (where the British Halley VI station is located) is largely made of reconstituted icebergs like you describe.

Of course, that shelf is also having some crack problems: https://www.theguardian.com/world/2016/dec/07/british-antarc...

No, not particularly. It's already floating, so it will just drift away for the most part. Some smaller bits will probably fall off and produce some spectacular waves. By smaller bits, I mean stuff up to a cubic kilometer, so I wouldn't want to be standing next to it when it happens.

This is all much further south than cruise ships normally go though.

Well, there's not a whole lot of factual difference between "Big Thing Could Happen" and "Big Thing Probably Won't Happen", and I know which one I'd lead with if I was an editor. I don't think there's anything in the article which I'd disagree with on a scientific level.

Nothing! This is a completely natural process - ice builds up over time in the shelf and it has to be lost somehow. The calving of the iceberg is, in itself, not a result of human activity.

If you mean more broadly how can we help prevent the loss of ice from Antarctica, then I'm not a climate policy expert, but https://350.org/ is a good place to start.

> * How long will it take for "Deleware" to melt?

Potentially a very long time, although it will likely break into smaller pieces first. A lot of icebergs get caught in the Antarctic Coastal Current, and just drift around the edge of Antarctica, not melting very much at all. Over time, most of them break free and drift north into warmer waters and melt, but others stick around. Iceberg B-9, which calved in 1987, still has a few chunks sitting around.

> * Is ocean ice this large called an iceberg?

Yes. You'll sometimes see the bigger bergs described as "ice islands", but that's just a subcategory of iceberg.

> * Does is get an official name, like IIS Wilmington (international ice station, capital of Deleware)?

It'll get a numeric designation, A-nn, where A indicates which quadrant of Antarctica it originated from (in this case 0-90W) and nn is a sequential number, probably in the high sixties depending on whether any other large bergs calve first. Then, as it breaks up, the resulting bergs will get letters added to the name, A-nnA, A-nnB, etc.

> * Have large ice sheets in the past forced/caused changes in human behavior, such as altering shipping lanes, in the same way planes fly around a storm?

In 2005, B-15A blocked the entrance to McMurdo Sound, where the main US and New Zealand Antarctic bases are located, and they were unable to get cargo ships in for a few weeks. And of course, ships are redirected around icebergs in the open ocean all the time.

Probably not. The Larsen B collapse was preceded by widespread surface melting across the shelf, which caused lots of crevasses to fill with water, driving them open, and the whole shelf pretty much shattered under the stress. We don't see that sort of melt on Larsen C - even though it's quite nearby, the climate is a couple of degrees colder.

A more probable (but still fairly unlikely) scenario is that this could destabilise the ice shelf over a longer timescale (maybe decades). Removing ice from the front would let the ice behind accelerate, stretch and thin, which makes it more vulnerable to calving again, and so forth.

The most likely outcome though is that there's no significant change to the ice shelf, except maybe the flow of the ice speeds up a bit, which is interesting glaciologically, but probably not something the rest of the world will get excited about.

Obviously, any and all of this could change as the climate continues to warm. If we start to see significant levels of surface melt ponding across the shelf, then we can worry.

Hey folks,

I'm one of the scientists on Project MIDAS (the team that made the announcement). Happy to answer questions about this. I've also been keeping a spreadsheet of things roughly the size of the iceberg, for journalistic comparisons: https://twitter.com/mewo2/status/818826891545210881

Yeah, that's sort of deliberate. Because the consonant system is so much more developed than the vowels, it's easier for them to do more of the heavy lifting, even if that is a bit unusual in natural language terms. I could probably stand to tweak the probabilities a bit though.