  We propose a scenario for launching relativistic jets from rotating black
holes, in which small-scale magnetic flux loops, sustained by disc turbulence,
are forced to inflate and open by differential rotation between the black hole
and the accretion flow. This mechanism does not require a large-scale net
magnetic flux in the accreting plasma. Estimates suggest that the process could
operate effectively in many systems, and particularly naturally and efficiently
when the accretion flow is retrograde. We present the results of
general-relativistic force-free electrodynamic simulations demonstrating the
time evolution of the black hole's magnetosphere, the cyclic formation of jets,
and the effect of magnetic reconnection. The jets are highly variable on
timescales ~ 10-10^3 r_ g/c, where r_g is the black hole's gravitational
radius. The reconnecting current sheets observed in the simulations may be
responsible for the hard X-ray emission from accreting black holes.
