  In this paper, we interpret the dark energy phenomenon as an averaged effect
caused by small scale inhomogeneities of the universe with the use of the
spatial averaged approach of Buchert. Two models are considered here, one of
which assumes that the backreaction term ${\cal Q}_\CD$ and the averaged
spatial Ricci scalar $\average{\CR}$ obey the scaling laws of the volume scale
factor $a_\CD$ at adequately late times, and the other one adopts the ansatz
that the backreaction term ${\cal Q}_\CD$ is a constant in the recent universe.
Thanks to the effective geometry introduced by Larena et. al. in their previous
work, we confront these two backreaction models with latest type Ia supernova
and Hubble parameter observations, coming out with the results that the
constant backreaction model is slightly favoured over the other model, and
within $1\sigma$ confidence interval of the parameter $n$ in the scaling
backreaction model, $\mid{\cal Q}_\CD\mid$ decreases with the increase of the
volume scale factor $a_\CD$ at adequately late times. Also, the numerical
simulation results show that the constant backreaction model predicts a smaller
expansion rate and decelerated expansion rate than the other model does at
redshifts higher than about 1, and both backreaction terms begin to accelerate
the universe at a redshift around 0.6. In addition, by confronting the standard
cosmological model against the same datasets, we find that the effective
geometry tends to push the constraint toward a smaller cosmological constant
term.
