There's a wonderful piece in the sad old Grauniad with some lovely maps on how the world would look with a rise in sea levels. For those of a historical turn of mind, their feature map of the Wash may look familiar... yes, it's exactly the same as the Anglian coastline back in Roman and Saxon times.
To be frank, I can see only upsides. With the Norfolk broads once again decently under water and connected to the sea, all those ugly floating caravans known as broads cruisers would be dashed to matchwood by decent storms. Hull would cease to be. Old Anglian cities - Dunwich, Soham and Ely - would again be prosperous ports.
Looks good to me.