  A non-vanishing entropy production rate is a hallmark of non-equilibrium
stationary states and is therefore at the heart of non-equilibrium
thermodynamics. It is a manifestation of a steady circulation $J_{\rm inv}$
along the level sets of the invariant density $\rho_{\rm inv}$, and is thus
generically used to quantify how far a steady system is driven out of
equilibrium. While it is well known that there exists a continuum of distinct
steady states with the same invariant measure, the question how the geometry
and topology of the invariant current a priori affect dissipation remained
elusive. For confined irreversible diffusions we identify two minimal
descriptors, the $\rho_{\rm inv}$-weighted vorticity and the variation of
$J_{\rm inv}$ along level sets of $\rho_{\rm inv}$, and prove that these
jointly bound from above the steady-state entropy production rate. In regions
where $\rho_{\rm inv}$ is close to Gaussian the bound is dominated solely by
the vorticity of the drift field and in the low-noise (Freidlin-Wentzel) limit
by any non-potential contribution to the drift, rendering $J_{\rm inv}$
virtually constant along the level sets of $\rho_{\rm inv}$.
