We didn’t really know–until now. The ocean, which has risen an average of 8 inches since 1900, should rise another 3 feet or so by 2100, but without an accurate record of where we started, we can’t know if the melting starts to speed up or (hopefully) slow down.
On the Climate Central website, Michael D. Lemonick quotes researcher Ian Joughin as saying, "There are lots of processes in play and it remains unclear whether the ice loss will level out or slow down or speed up. We thought we understood ice sheets, but it’s clear we don’t. We need a lot more observations and a lot better modeling."