  Accretion discs around black holes power some of the most luminous objects in
the Universe. Discs that are misaligned to the black hole spin can become
warped over time by Lense-Thirring precession. Recent work has shown that
strongly warped discs can become unstable, causing the disc to break into
discrete rings producing a more dynamic and variable accretion flow. In a
companion paper, we present numerical simulations of this instability and the
resulting dynamics. In this paper, we discuss the implications of this dynamics
for accreting black hole systems, with particular focus on the variability of
Active Galactic Nuclei (AGN). We discuss the timescales on which variability
might manifest, and the impact of the observer orientation with respect to the
black hole spin axis. When the disc warp is unstable near the inner edge of the
disc, we find quasi periodic behaviour of the inner disc which may explain the
recent quasi periodic eruptions observed in, for example, the Seyfert 2 galaxy
GSN 069 and in the galactic nucleus of RX J1301.9+2747. These eruptions are
thought to be similar to the `heartbeat' modes observed in some X-ray binaries
(e.g. GRS 1915+105 and IGR J17091-3624). When the instability manifests at
larger radii in the disc, we find that the central accretion rate can vary on
timescales that may be commensurate with, e.g., changing-look AGN. We therefore
suggest that some of the variability properties of accreting black hole systems
may be explained by the disc being significantly warped, leading to disc
tearing.
