  Early in the study of viscous accretion disks it was realized that energy
transfers from distant sources must be important, not least because the flow at
the disk midplane in the bulk of the disk is likely outwards, out of the
gravitational potential well. If the source of the viscosity is powered by
accretion, such as in the case of the magneto-rotational instability, such
distant energy sources must lie in the innermost regions of the disk, where
accretion occurs even at the midplane. We argue here that modulations in this
energy supply can alter the accretion rate on dynamical, rather than far longer
viscous, time scales. This means that both the steady state value of and
fluctuations in the inner disk's accretion rate, depending on the details of
the inner boundary condition and occurring on the inner disk's rapid evolution
time, can affect the outer disk. This is particularly interesting because
observations have shown that disk accretion is not steady (e.g.~EX Lupi type
objects). We also note that the power supplied to shearing boxes is set by the
boxes themselves rather than the physical energy fluxes in a global disk. That
is, their saturated magnetic field is not subject to the full set of energy
constraints present in an actual disk. Our analysis suggests that large scale
radial transport of energy has a critical impact on the evolution and
variability of accretion disks.
