In the article (behind paywall)
http://www.nature.com/ncomms/2014/140925/ncomms6076/full/ncomms6076.htmlauthors present comparisons between Arctic and Antarctic drill core records and a new dataset they've obtained from bottom of the Red Sea, the salinity of which (somewhat) complicatedly, conforms to global sea levels. Further comparisons were made against paleoclimatological Asian Monsoon record. Speeds of the natural sea level rises during changes in the recent Pleistocene could thus be estimated.
Eelco Rohling (One of the authors) summarizes their findings at Skeptical Science:
http://www.skepticalscience.com/news.php?n=2694 the final chapter is as follows:"But that time has come and, once ice sheets start to melt, the freight train is in motion. It will then keep moving for many centuries to come, no matter how hard we stamp on the brakes."