[GWSG] Sea level rise + subsidence; the AMOC and sea level rise

[Tilley, Al]

1. Models of sea level rise show much less than the historical record indicates for our state of heating. The historical record may have been somewhat misread, due to land movements under pressure of ice sheets, according to a new study from the Lamont-Doherty Earth Observatory. By their conclusions, our expectations of sea level rise should be brought closer to the models. On the other hand, the study was based on a single region, and conditions in the last interglacial may have differed in their impact from the current conditions. The study is best viewed as a new hypothesis rather than a new projection.
The article is a good illustration of the difficulties of anticipating sea level rise accurately. For one thing, it implies that we need projections of land subsidence, which will vary by region, in addition to projections of sea level rise. What we will actually experience will combine subsidence with sea level rise. If I read this correctly, the historical figures accurately reflect the combination, though on a relaxed time scale. We should be suspicious of estimates which give us the sea level rise alone. That makes an enormous difference for our planning. I hope someone will correct me if they see more clearly.  https://phys.org/news/2021-08-sea-high-thought-landmasses.html

2. While I am thinking of planning for sea level rise: recent research indicates a destabilization of the AMOC. Slowing of the current leads to instantaneous sea level rise on the US East Coast. https://www.gfdl.noaa.gov/wp-content/uploads/2016/08/04.02_Jianjun_Yin.pdf
The Gulf Stream, a part of the AMOC, “keeps sea level on the US East Coast 3-5 feet lower than water offshore. . ..” http://www.ces.fau.edu/gulfstream/pdfs/ezer.pdf
The AMOC seems poised to drop to a lower intensity.  If the recent slowdown is sign of actual loss of dynamical stability, that “would imply that the AMOC has approached its critical threshold beyond which an abrupt and potentially irreversible transition to the weak mode could occur.” (Niklas Boers, lead author.) https://phys.org/news/2021-08-ocean-current-approaching.html
When the current strong circulation collapses, we may expect an immediate and permanent rise, perhaps of a foot to a few feet on the East Coast, depending on the new configuration of the AMOC.  Since the best-informed opinion is that the tipping point could be crossed at any time within the next couple of decades, should we not include that possibility in our planning? We should be estimating the likely magnitude of the rise. If you know of someone who is going about that, please let me know.

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