Moving inland is a good thing. We should commence as soon as possible. Advisable steps would include:
* not building anything new in coastal areas that will be inundated
* beginning the move by building only on the inland side of coastal settlements
* closing vulnerable facilities promptly (hospitals, daycares, etc.) and moving them inland
* looking into how we might route people first to areas currently suffering from depopulation
* building as much affordable housing as possible in the Midwest and Mountain areas
* offering incentives for people to move away from the areas most at risk for flooding, violent storms, and while we're at it wildfires and water shortages
* discouraging anyone from moving into areas of high threat
I don't advocate using force. It is inefficient and unethical, usually causing more problems than it can solve. But there are lots of places like Illinois, West Virginia, and Wyoming that are losing people yet safe to live in. Shifting people there is a win-win.
See also my Rutledge thread in Polychrome Heroics about settling Syrian refugees in Vermont, where many towns are dwindling.
We have people that need places; we have places that need people; it is civilization's job to put those together. Fail and die.