  We consider the back-reaction of cosmological fluctuations on the local
expansion rate averaged over a space-like hypersurface of constant value of a
clock field. We show that in the infrared limit, the fluctuations lead to a
decrease in the average expansion rate, measured at a fixed value of the clock
field, compared to what would be obtained in a homogeneous universe. We work in
the context of Einstein gravity coupled to perfect fluid matter.
