And it's worth noting, something like 450,000,000 people live within 5m of sea level. This would be absolutely catastrophic for the entire world. A significant contributing factor to European political strife over the past decade has been the arrival of refugees from other regions; and Europe is currently home to about 22 million refugees[0]. It's hard to imagine how wealthier regions will cope with the influx of 450,000,000 refugees (admittedly, many will be staying within their home regions -- but many will likely not).
[0] https://reporting.unhcr.org/operational/regions/europe