Consistency of the local Hubble constant with the cosmic microwave
  background
  A significant tension has become manifest between the current expansion rate
of our Universe measured from the cosmic microwave background by the Planck
satellite and from local distance probes, which has prompted for
interpretations of that as evidence of new physics. Within conventional
cosmology a likely source of this discrepancy is identified here as a matter
density fluctuation around the cosmic average of the 40 Mpc environment in
which the calibration of Supernovae Type Ia separations with Cepheids and
nearby absolute distance anchors is performed. Inhomogeneities on this scale
easily reach 40% and more. In that context, the discrepant expansion rates
serve as evidence of residing in an underdense region of $\delta_{\rm
env}\approx-0.5\pm0.1$. The probability for finding this local expansion rate
given the Planck data lies at the 95% confidence level. Likewise, a
hypothetical equivalent local data set with mean expansion rate equal to that
of Planck, while statistically favoured, would not gain strong preference over
the actual data in the respective Bayes factor. These results therefore suggest
borderline consistency between the local and Planck measurements of the Hubble
constant. Generally accounting for the environmental uncertainty, the local
measurement may be reinterpreted as a constraint on the cosmological Hubble
constant of $H_0=74.7^{+5.8}_{-4.2}$ km/s/Mpc. The current simplified analysis
may be augmented with the employment of the full available data sets, an impact
study for the immediate $\lesssim10$ Mpc environment of the distance anchors,
more prone to inhomogeneities, as well as expansion rates measured by quasar
lensing, gravitational waves, currently limited to the same 40 Mpc region, and
local galaxy distributions.
