  Experiments on the distributions of switching currents in Josephson junctions
are sensitive probes of the mechanism by which a junction changes abruptly to a
finite voltage state. At low temperatures data exhibit smooth and gradual
deviations from the expectations of the classical theory of thermal activation
over the barrier in the tilted washboard potential. In this paper it is shown
that if a very small proportion of the noise energy entering the apparatus at
room temperature survives filtering and reaches the sample, it can enhance the
escape rate sufficiently to replicate experimental observations of the
temperature dependence of the switching bias. This conjecture is successfully
tested against published experimental data.
