consider how to prepare for a relatively rapid, as such things go, sea level rise of 3 meters, conceivably more, over the next 20 years

Report of the Delta Committee - page 24 for scenarios which are considerably worse than the IPCC scenarios.

Unless you actually mean a sea level rise of 3 meters in the coming 20 years - which is in the range of possible as the sun not rising tomorrow and therefore can't be planned for.