  We show that in the SU(2) Georgi-Glashow model, 't Hooft-Polyakov monopoles
are produced by a classical instability in magnetic fields above the
Ambjorn-Olesen critical field, which coincides approximately with the field at
which Schwinger pair production becomes unsuppressed. Below it, monopoles can
be produced thermally, and we show that the rate is higher than for pointlike
monopoles by calculating the sphaleron energy as a function of the magnetic
field. The results can be applied to production of monopoles in heavy-ion
collisions or in the early Universe.
