  We argue that the X-ray and UV flux illuminating the parsec-scale accretion
disk around luminous active galactic nuclei (AGN) is super-Eddington with
respect to the local far-infrared dust opacity. The far infrared opacity may be
larger than in the interstellar medium of the Milky Way due to a combination of
supersolar metallicity and the growth of dust grains in the dense accretion
disk. Because of the irradiating flux, the outer accretion disk puffs up with a
vertical thickness $h\sim R$. This provides a mechanism for generating a
geometrically thick obscuring region from an intrinsically thin disk. We find
obscuring columns $\sim 10^{22} - 10^{23} {\rm cm}^{-2}$, in reasonable
agreement with observations.
