Rob LarterJan 26
Some people on various social media platforms have been claiming that something dramatic is about to happen at Thwaites Glacier, and implying that this will result of an abrupt rise is sea level within a few years. So what's really going on? 🧵
Show threadRob LarterJan 26
Through the International Thwaites Glacier Collaboration more than a hundred researchers have been conducting studies on many aspects of the glacier over the past six years. Overall, our results paint a grim picture for the future of the glacier and thus the wider West Antarctic Ice Sheet.
We expect the rapid retreat of the glacier observed over the past couple of decades to continue and to accelerate during the latter part of this century and beyond. This sector of West Antarctica will contribute increasingly to an accelerating rate of global sea-level rise.
Show threadRob LarterJan 26
The current changes that some people are getting agitated about are occurring on the small remnant of ice shelf - a floating extension - that projects from the front of Thwaites Glacier. The ice shelf has been progressively thinning and fracturing over many years.
Until a couple of years ago there were two distinct sectors of ice shelf in front of Thwaites Glacier, separated by a "shear zone" that allowed them to move independently. In front of the fast-flowing central axis of the glacier the Thwaites Glacier Tongue repeatedly grew and broke off.
Show threadRob LarterJan 26
Up until the early years of this century the Glacier Tongue typically grew to a length of more than 70 km before calving as a giant tabular iceberg. The last tongue became iceberg B22a. In more recent years it has extended a much shorter distance before each time it broke off.
Ice flowing from the axis of the glacier is now highly fractured, so instead of forming a tongue it breaks very soon after flowing into the ocean. As a result, this part of the glacier is now fronted by a mélange of icebergs (typically 1-2 km across) and sea ice.
Show threadRob LarterJan 26
This leaves the Thwaites Eastern Ice Shelf, which extends from the slower flowing eastern part of the glacier, as the only intact area of ice shelf at the front of the glacier.
Several years ago scientists studying the Thwaites Eastern Ice Shelf as part of the International Thwaites Glacier Collaboration identified that changes underway there would lead to it being lost soon, probably within 10 years.
https://doi.org/10.5194/tc-16-397-2022
Weakening of the pinning point buttressing Thwaites Glacier, West Antarctica

Abstract. The Thwaites Eastern Ice Shelf buttresses a significant portion of Thwaites Glacier through contact with a pinning point 40 km offshore of the present grounding line. Predicting future rates of Thwaites Glacier’s contribution to sea-level rise depends on the evolution of this pinning point and the resultant change in the ice-shelf stress field since the breakup of the Thwaites Western Glacier Tongue in 2009. Here we use Landsat-8 feature tracking of ice velocity in combination with ice-sheet model perturbation experiments to show how past changes in flow velocity have been governed in large part by changes in lateral shear and pinning point interactions with the Thwaites Western Glacier Tongue. We then use recent satellite altimetry data from ICESat-2 to show that Thwaites Glacier’s grounding line has continued to retreat rapidly; in particular, the grounded area of the pinning point is greatly reduced from earlier mappings in 2014, and grounded ice elevations are continuing to decrease. This loss has created two pinned areas with ice flow now funneled between them. If current rates of surface lowering persist, the Thwaites Eastern Ice Shelf will unpin from the seafloor in less than a decade, despite our finding from airborne radar data that the seafloor underneath the pinning point is about 200 m shallower than previously reported. Advection of relatively thin and mechanically damaged ice onto the remaining portions of the pinning point and feedback mechanisms involving basal melting may further accelerate the unpinning. As a result, ice discharge will likely increase up to 10 % along a 45 km stretch of the grounding line that is currently buttressed by the Thwaites Eastern Ice Shelf.

Show threadRob LarterJan 26
Since this research began, a new shear zone that cuts diagonally across the ice shelf has developed rapidly, allowing flow of the main part of the ice shelf to accelerate. This has resulted in substantial change over the past two and a half years, as shown by this pair of Sentinel-1 images.
Show threadRob LarterJan 26
Here are those two images as an animated gif, clearly showing the changes that have occurred from September 2022 until now. So what does this mean for the future of the ice shelf and the glacier itself?
Show threadRob LarterJan 26
The ice shelf is undoubtedly going through its death throes. Breakup events observed on other ice shelves show the exact timing of final break up is impossible to predict. Fortunately, however, unlike many other ice shelves, this one has not been doing much recently to slow the flow of the glacier.
Over the past couple of years, while the ice shelf has accelerated seaward, the rate of flow of the glacier has not increased in response. The fact that this ice shelf is not holding back the glacier is shown most clearly by the development of large rifts across the upstream part of the ice shelf.
These observations are described further in this explainer article and the research paper it includes a link to.
https://thwaitesglacier.org/news/thwaites-eastern-ice-shelf-cracks-spread-not-because-melting
ITGC Thwaites Glacier

cobalt going beige todayJan 26
Show threadRob Larter
So in summary, yes the Thwaites Eastern Ice Shelf is expected to be lost sometime over the next couple of years, perhaps even this Antarctic summer. However, this is not expected to result in an abrupt increase in the rate of ice loss from the glacier.
In the longer term though, over the rest of this century and beyond, the outlook from Thwaites Glacier and the wider West Antarctic Ice Sheet is grim. Progressively increasing rates of ice loss, contributing to an accelerating rate of global sea-level rise, are expected.
Jan 26 at 3:17pmWeb