Due to the non-commutation of spatial averaging and temporal
evolution, inhomogeneities and anisotropies (cosmic structures)
influence the evolution of the averaged Universe via the
cosmological backreaction mechanism. We study the backreaction
effect as a function of averaging scale in a perturbative approach
up to higher orders. We calculate the hierarchy of the critical
scales, at which 10% effects show up from averaging at different
orders, observable up to scales of 200 Mpc. The cosmic
variance of the local Hubble rate is 10% (5%) for spherical
regions of radius 40 (60) Mpc. We compare our results to
the Hubble Space Telescope (HST) Key Project data.