You are looking at a very small fraction of the problem. Yes higher water is not an extinction level event.

But with increased CO2 there's also increasing acidification. So the plankton dies, coral dies, mollusks die (their shells erode). The food web at sea dies.... as does the food for a decent fraction of the planet. Acid rain causes more damage, food production becomes tougher... especially on the decreasing number of acres above flood level. Much of the most productive farm land in the world would be inundated with acidic salty water.

There is a great book by a marine biologist that goes into detail about these topics. It's called The Ocean of Life - The Fate of Man and the Sea by Callum Roberts. It was recommended to me here on HN several years ago, and I think that recommendation bears repeating. He goes into great detail about conservation topics for half the book, and the other half has to do with climate change and its effects on the oceans (and how that affects humanity).

I think what a lot of people miss as well is a lot of our oxygen output comes from life in the ocean. I don't know real numbers here or what other consequences this entails (just wanted to point it out).

Also, don't discount the rising level of violent conflicts that will ensue for shrinking resources.

Conflicts don't cause extinction. The winner survives.

Not necessarily. We all know of the theory of Mutually Assured Destruction.

As an analogy, think about what happens if a deadly infectious bacteria or virus "wins" by infecting every human on earth. If there is no cure and no human has an adaptation or mutation to stop it, by winning it has sowed the seeds of its own destruction because there are no more hosts to infect.

It is easy to imagine several scenarios where an all out war for dwindling resources can lead to extinction.

Unsettling existing populations increases chances of political instability and potential war. You can see the reaction to migrations and refugees (Syria, for example) now. That could quite easily be magnified if larger populations were forced to desperate measures. War is a species-ending risk, IMO.

Should I start buying 215 foot above sea level for future beachfront development?

Maybe if you want the place to be in 1 foot of water?

Um...

https://en.wikipedia.org/wiki/Clathrate_gun_hypothesis

213 feet??

Global warming is causing the destruction of whole ecosystems, any of which might lead to a chain-reaction that undoes biological infrastructure that entire species rely upon, including humans. Many species have already been ended, so I'm not sure why you believe it's not a species-ending problem. Mass migration also means the movement of predators into territories with unadapted prey, which can also result in extinction. (The Dodo went extinct due to habitat destruction and the introduction of predatory mammals, for example.) Almost every extinction in the history of Earth has been a result of global climate changes.

I don't understand why you're being so myopic? The worst case isn't a few people having to buy new homes, it's mass extinction and war. Which may as well be total nuclear war, as far as you or I can predict.