It depends on how close you get to the glaciers (on most days).
Most glacier days I am outside all day, wearing a jacket and ear protection. It can be cold and windy.
Though - I have to say there was one day when I was at Glacier Bay and it was incredibly warm. I looked over and people were sunning in the pool area and swimming. Anything can happen.
I haven't gotten close to Hubbard Glacier for awhile. So on those days, I can't tell a difference.
Mendenhall glacier (when you visit via bus/car) usually isn't that cold. It is the temp it usually is in Juneau. If you land on the glacier via helicopter, expect an entirely different answer.
Be prepared - dress in layers.