  From the early radiation of type II-P supernovae (SNe), it has been claimed
that the majority of their red supergiant (RSG) progenitors are enshrouded by
large amounts of circumstellar material (CSM) at the point of explosion. The
inferred density of this CSM is orders of magnitude above that seen around RSGs
in the field, and is therefore indicative of a short phase of elevated
mass-loss prior to explosion. It is not known over what timescale this material
gets there: is it formed over several decades by a `superwind' with mass-loss
rate $\dot{M} \sim10^{-3}\,{\rm M_\odot\,yr^{-1}}$; or is it formed in less
than a year by a brief `outburst' with $\dot{M}\sim10^{-1}\,{\rm
M_\odot\,yr^{-1}}$? In this paper, we simulate spectra for RSGs undergoing such
mass-loss events, and demonstrate that in either scenario the CSM suppresses
the optical flux by over a factor of 100, and that of the near-IR by a factor
of 10. We argue that the `superwind' model can be excluded as it causes the
progenitor to be heavily obscured for decades before explosion, and is strongly
at odds with observations of II-P progenitors taken within 10 years of
core-collapse. Instead, our results favour abrupt outbursts $<$1 year before
explosion as the explanation for the early optical radiation of II-P SNe. We
therefore predict that RSGs will undergo dramatic photometric variability in
the optical and infrared in the weeks-to-months before core-collapse.
