More than they should by what measure? These glaciers have been studied for perhaps a few decades and they have likely existed for centuries. Yet they can determine exactly how fast they should melt at any given time in their existence.
By that logic, the glaciers that covered much of the northern US and Canada must have melted quite a bit more than they should so many years ago when the "warming" really got started. There are many things we can't explain but blaming our actions is akin to our early ancestors believing they caused an eclipse or a drought.
The Ice Age ended when humanids invented fire and created vast ozone clouds. History repeats itself.