What is not new
Ultimately sea levels will rise several feet, given the present levels of CO2 in the atmosphere. We already knew this by examining paleo data, and finding periods in the past with similar surface temperatures and/or similar atmospheric CO2 levels as today.
I put a graphic from a paper by Gavin Foster and Eelco Rohling at the top of the post. It does a good job of summarizing the paleo data.
If we keep pumping CO2 into the atmosphere at current, or even somewhat reduced,...