  In the context of averaged cosmologies, the effective equations can be
written in the form of "regional" Friedmannian equations with additional
sources arising from the so-called backreaction of inhomogeneities. We propose
a mean field description of this backreaction in terms of a regionally
homogeneous scalar field: this provides a physical motivation to the
phenomenological scalar fields generically called quintessence fields. We
explicitly reconstruct the potential of the scalar field for a one-parameter
family of scaling solutions to the backreaction problem, showing that it
entails most of the standard scalar fields including e.g. standard and phantom
quintessence scenarii.
