  We first compare different approaches to estimates of the magnitude of the
chiral magnetic effect in relativistic heavy ion collisions and show that their
main difference lies in the assumptions on the length of persistence of the
magnetic field generated by the colliding nuclei. We then analyze recent
measurements of the global polarization of $\Lambda$ and $\bar \Lambda$
hyperons in terms of the bounds they set on the magnitude of the late time
magnetic field.
