The melting of the ice-caps over the next 100 years or whatever will result is rising sea levels. Potentially a rise of hundreds of metres.
The additional energy in the atmosphere leads to heavier rains, and hence more runoff. When that runoff goes through a building we call that flooding.
In other places a lack of rain is leading to water shortage and drought.
Sea level rise is long term, flooding and droughts are here now. In the short term we need to allow water more space to flow. Retreating from the waters edge can be done, and it can be paid for "collectively". It's a relatively small-scale action, and it can happen progressively year on year.
Simple rules to condem areas after say a second flooding would be a start.
Retreating from a 100m sea level rise is too large a scale to contemplate. Sure it'll happen "slowly" but the number of people involved is a sizeable fraction of all humanity.
Inland small towns everywhere should be considering planning and zoning that would happen if they grew by a million people. New cities, on the new waters edge, will be created from nothing.
At this point we can stretch out the time line, but I think the course is set. There's no putting the genie back in the bottle now.
But I'm confident we will adapt. This isn't an extinction event. Humans adapt better than anything else.