  The pumping conductance of a disordered two-dimensional Chern insulator
scales with increasing size and fixed disorder strength to sharp plateau
transitions at well-defined energies between ordinary and quantum Hall
insulators. When the disorder strength is scaled to zero as system size
increases, the "metallic" regime of fluctuating Chern numbers can extend over
the whole band. A simple argument leads to a sort of weighted equipartition of
Chern number over minibands in a finite system with periodic boundary
conditions: even though there must be strong fluctuations between disorder
realizations, the mean Chern number at a given energy is determined by the {\it
clean} Berry curvature distribution expected from the intrinsic anomalous Hall
effect formula for metals. This estimate is compared to numerical results using
recently developed operator algebra methods, and indeed the dominant variation
of average Chern number is explained by the intrinsic anomalous Hall effect. A
mathematical appendix provides more precise definitions and a model for the
full distribution of Chern numbers.
