Miami isn’t going anywhere for at least a few hundred years, by which point they will have plenty of time/tech to keep things above water. The most likely models show 1 to 4.3 feet of rise by 2100 compared to 2000 [0] which has relatively low impact on miami other than the miami beach [1] which is already making plans for keeping/getting flood and rain waters out.

[0]https://www.climate.gov/news-features/understanding-climate/...

[1]https://coast.noaa.gov/slr/#/layer/slr/3/-8927718.607502826/...

Sea level rise will be unevenly distributed, because of gravitational, rebound, and other effects. That tool helpfully provides local scenarios, and the "intermediate high" scenario for Miami Beach corresponds to 6 feet of sea level rise by 2100 [0].

[0] https://coast.noaa.gov/slr/#/layer/sce/2/-9015288.864066828/... (select "view by scenario")

The highest probability model (intermediate) shows 3.7 feet of rise by 2100 which again really only affects the beach area, if you look at intermediate high (lower probability of corresponding to reality) scenario it starts to hit at some of the areas around the miami river, but again this is far cry from miami being definitively underwater and does not account for riverwalls, floodwalls that are being planned and installed.

The different scenarios are not constructed to represent the probability distribution of likely outcomes, and the "intermediate" scenario does not represent the "highest probability model".

Indeed, given that unpredictable human behaviour is the main driver of the response, it is very difficult to construct a "most likely scenario". Instead, what can be said is "given an emissions scenario (or range of scenarios), these are the probabilities of different outcomes". The sea level rise scenarios themselves only describe the outcomes, and do not correspond to the probabilities.

The mapping between emissions scenarios and outcomes can be found in Table 4 here [0]. You may note that for low emissions scenarios the exceedance probabilities don't look too bad, but there is still considerable risk.

[0] https://tidesandcurrents.noaa.gov/publications/techrpt83_Glo...

Sea level rise can be extremely nonlinear. There are glaciers in Antarctica that are like the cork in the wine bottle. If the "gatekeeper glacier" is gone, the sea water gets into the basin that's below sea level and will melt all the multi kilometer thick ice in that basin.

Each can provide meters of sea level rise. You can check out Eric Rignot's presentations from youtube.

We don't know if the melting of such a gatekeeper glacier will take ten, fifty or a hundred years. But it has started.

You can't extrapolate this effect from just looking at recent past temperature and sea level rise - it's a whole different mechanism.

Not to mention, many parts of Miami are already built on artificial land. My uncle's place is in East Fort Lauderdale, which is an artificial network of peninsulas. sort of like this [1] but connected to land. New houses are build higher. Realistically I think accommodating rising sea levels is going to be accommodated incrementally by new development.

1. https://en.m.wikipedia.org/wiki/Palm_Islands#:~:text=The%20P....

I don't think I have that much need for precision. But it would be good to have at least some analysis of the costs of an additional 0.5 degree increase, given that limiting climate change is one of the biggest global efforts right now, and the costs of that effort. And maybe that analysis exists, but if so I haven't seen it. We shouldn't be having these big global efforts without clearly explaining to the public exactly why it is worth the investment over other things we could be investing in to improve global health.

If there is a good chance food production will drop significantly with the additional 0.5 degree, it probably makes sense to invest a lot to meet the goal of 1.5 vs 2.0. If the main concern is flooding and a smaller drop in food production, it might make more sense to invest in more intensive farming (we are certainly nowhere near the ceiling of easy gains here) and better infrastructure.

How much would a sea wall around Miami or Shanghai cost?

A sea wall around Miami wouldn't help due to the karst substrate; water would flow through the limestone channels under any wall. The main concern with sea level rise in South Florida isn't that the seawater will come in but that rainwater won't drain away. There will have to be a huge investment in pumping systems.

That investment is likely cheaper and more feasible than geo-engineering the globe's climate.