  The evolution of circumbinary discs and planets is often studied using
two-dimensional (2D) numerical simulations, although recent work suggests that
3D effects may significantly alter the structure of the inner cavity created by
the binary. In this study, we present the results of 3D hydrodynamical
simulations of circumbinary discs that orbit around analogues of the Kepler-16
and Kepler-34 systems, including the effect of stellar heating and radiative
cooling on the thermal disc structure. We find that compared to their 2D
counterparts, the structures of the cavities in 3D circumbinary disc models
appear to reach a quasi-stationary state more rapidly, and in a subset of our
runs the evidence for this is unambiguous. Furthermore, the sizes and
eccentricities of the inner cavity are smaller in 3D compared to 2D. We
attribute this difference to enhanced spiral wave dissipation in disc regions
above the midplane, where the cooling time is of the order of the dynamical
timescale, resulting in smaller inner cavity sizes in 3D disc models. Our
results suggest that migrating planets should park closer to the central binary
in 3D models of circumbinary discs, and point to the importance of including
the 3D structure when simulating circumbinary discs and planets.
