  The polarity of the toroidal magnetic field in the solar convection zone
periodically reverses in the course of the 11/22-year solar cycle. Among the
various processes that contribute to the removal of `old-polarity' toroidal
magnetic flux is the emergence of flux loops forming bipolar regions at the
solar surface. We quantify the loss of subsurface net toroidal flux by this
process. To this end, we determine the contribution of an individual emerging
bipolar loop and show that it is unaffected by surface flux transport after
emergence. Together with the linearity of the diffusion process this means that
the total flux loss can be obtained by adding the contributions of all emerging
bipolar magnetic regions. The resulting total loss rate of net toroidal flux
amounts to 1.3 X 10^{15} Mx/s during activity maxima and 6.1 X 10^{14} Mx/s
during activity minima, to which ephemeral regions contribute about 90% and
97%, respectively. This rate is consistent with the observationally inferred
loss rate of toroidal flux into interplanetary space and corresponds to a decay
time of the subsurface toroidal flux of about 12 years, also consistent with a
simple estimate based on turbulent diffusivity. Consequently, toroidal flux
loss by flux emergence is a relevant contribution to the budget of net toroidal
flux in the solar convection zone. That the toroidal flux loss rate due to flux
emergence is consistent with what is expected from turbulent diffusion, and
that the corresponding decay time is similar to the length of the solar cycle
are important constraints for understanding the solar cycle and the Sun's
internal dynamics.
