It is very easy to zoom out an fit a line but the step like changes at certain points are interesting. Averaging over the variations might throw away a lot of interesting information.

But you are right about one thing, the curve has not dipped up appreciably in the last 30 years. All I see are steps, plateau's where the level is kept before the next drop.

EDIT: can't do math or I keep thinking it's 2000's still.