  We study both monolayer and bilayer graphene transport properties taking into
account the presence of correlations in the spatial distribution of charged
impurities. In particular we find that the experimentally observed sublinear
scaling of the graphene conductivity can be naturally explained as arising from
impurity correlation effects in the Coulomb disorder, with no need to assume
the presence of short-range scattering centers in addition to charged
impurities. We find that also in bilayer graphene correlations among impurities
induce a crossover of the scaling of the conductivity at higher carrier
densities. We show that in the presence of correlation among charged impurities
the conductivity depends nonlinearly on the impurity density $n_i$ and can even
increase with $n_i$.
