Building flood barriers is a lot cheaper and a lot easier to throw money at than reducing emissions. Barriers can also be constructed on a local or regional level, whereas emission reduction requires achieving an intractable global consensus. It doesn’t follow that the same dysfunctions that have prevented emission reduction will prevent the construction of flood barriers.
Putting up barriers won't stop the water rising. And the vast majority of small island nations won't be able to afford to wall off their entire landmass
As mentioned above, places with porous geology that have low elevation even well inland are not salvageable. And the vast majority of small island nations don’t contain very many people. It seems like the goalposts are being moved here from “sea level rise is an existential threat to human civilization” to “sea level rise will disrupt the way of life of some people”.
