  We use cosmological perturbation theory to study the backreaction effects of
a self-consistent and well-defined cosmological averaging on the dynamics and
the evolution of the Universe. Working with a perturbed
Friedman-Lemaitre-Robertson-Walker Einstein-de Sitter cosmological solution in
a comoving volume-preserving gauge, we compute the expressions for the
expansion scalar and deceleration parameter to second order, which we use to
characterize the backreaction. We find that the fractional shift in the Hubble
parameter with respect to the input background cosmological model is
Delta~10^{-5}, which leads to an effective energy density of the order of a few
times 10^{-5}. In addition, we find that an appropriate measure of the
fractional shift in the deceleration parameter Q is very large.
