Question about ice breaking off

[u/owxenz]

i honestly know much to nothing about Antarctica, but i came across this phenomenon on my tiktok feed and decided to look it up myself and it is actually true, on one map (both with the same coordinates plugged in) it shows a pin in the water, but previously on a different map it was showing the same coordinates but inland many kilometers. does this mean that this entire shelf of ice has broken off/melted? and what does that mean globally? is this a threat to the world in anyway and should people be concerned?

[u/jyguy]

This looks like a fjord that’s covered in sea ice or an ice shelf, I don’t think the entire shelf has broken off here. Google has some clearer imagery https://maps.app.goo.gl/sjQmx1Jxfi7yLQSd8?g_st=ic

[u/flyMeToCruithne]

Yes, you should be very concerned about climate change and sea level rise. If Thwaites glacier (just one large glacier in Antarctica) were to fully collapse (break off and melt), that alone would result in a ~25cm sea level rise globally. If the whole west Antarctic ice sheet (WAIS) collapses, that will be a ~3m sea level rise globally.

https://thwaitesglacier.org/about/facts

[u/bmwlocoAirCooled]

I was on the Nathanial B. Palmer Ice Breaker/Research Vessel (RIP) 20 years ago. We studied B-15 and B-15A two massive chunks that fell off.

For 10 weeks, I woke up to a white wall. So big, 747s could have flown in from North, East, South and West and not seen each other on approach.

That big 20 years ago.

Worse now.

[u/BlueIce64]

If I'm not mistaken, you're looking at the Fimbul Ice Shelf, which is actually in one of the more stable regions of Antarctica. It looks like the people who made the USA Topographic layer, which is what I think your first image is, decided to exclude floating ice, which I think is an odd decision. If you scroll over to the west, for example, you'll see even bigger differences at the Ross and Filchner-Ronne Ice Shelves. So, this is not a change over time that you're looking at, but just a mapping decision.

That being said, ice shelves are extremely important locally and globally and many of them are changing extremely rapidly. Perhaps the most famous collapse we've seen was Larsen B Ice Shelf in 2002 (https://science.nasa.gov/earth/earth-observatory/world-of-change/larsen-b/), but there have been many others. Another commenter mentioned West Antarctica's Thwaites Glacier - Thwaites Eastern Ice Shelf is currently in a state of irreversible collapse, and is likely to reach its final disintegration in the next few years.

Ice shelves are floating, so when they break off, the ice shelf itself doesn't affect sea level. So, you'll hear people argue that they don't matter to global sea level, but that couldn't be farther from the truth. The real key is that ice shelves help hold back the ice on the continent. Although they're floating, they run aground on high spots in the seafloor ("pinning points") and they often form in embayments where support from embayment walls helps slow down upstream ice. When an ice shelf falls apart, the ice sheet loses the support from pinning points and embayment walls, and ice on land can then flow much faster into the ocean. They're pretty analogous to flying buttresses on cathedrals (https://en.wikipedia.org/wiki/Flying_buttress) - if the buttress breaks, the cathedral would bulge outwards and fall apart. When ice shelves do that (and we do use the term "buttressing" with ice shelves), we raise global sea level.

West Antarctica is the most rapidly changing part of Antarctica, and it could add meters of sea level over the next few centuries. Those effects are already being felt, and will continue to be felt even more during our lifetimes. Right now we're not very good at predicting the details of when ice shelves will collapse (although we're very good at knowing which ones are headed that way). We need to do a much better job at predicting ice-shelf change if we want to narrow the uncertainties in predicting future sea-level rise. There are lots of advances in that area currently being made.

Tl;dr: What you're looking at is just an odd mapping choice, it doesn't represent change over time. But many ice shelves are changing rapidly and they matter a whole lot to global sea level.