I had found the argument put forward by Curry persuasive (although I read it elsewhere). But when I read into the subject more, and came across the paper I linked to, I was less certain.
On balance I do think that AGW's forcing has been going on for much longer than the last few decades. As persistent ice integrates impacts upon it (it's persistence from year to year means it holds a 'memory' of all impacts upon it), it is much more sensitive than seasonal ice or ice that is replenished. Here I mean ice that either grows during a cold period, or ice in outlet glaciers.
The ice sheets, having been persistent ice, therefore were probably more sensitive to small early years anthropogenic forcing.
However this isn't as strong an argument as implying the ice shelf loss happened in the last several decades, which by my reading is factually incorrect. Massive loss of shelf area seems to have been happening during the first half of the Twentieth century.
PS - see figure 3 of the paper I linked to in my previous comment.