  We use magnetohydrodynamical simulations of converging warm neutral medium
flows to analyse the formation and global evolution of magnetised and turbulent
molecular clouds subject to supernova feedback from massive stars. We show that
supernova feedback alone fails to disrupt entire, gravitationally bound,
molecular clouds, but is able to disperse small--sized (~10 pc) regions on
timescales of less than 1 Myr. Efficient radiative cooling of the supernova
remnant as well as strong compression of the surrounding gas result in
non-persistent energy and momentum input from the supernovae. However, if the
time between subsequent supernovae is short and they are clustered, large hot
bubbles form that disperse larger regions of the parental cloud. On longer
timescales, supernova feedback increases the amount of gas with moderate
temperatures (T~300-3000 K). Despite its inability to disrupt molecular clouds,
supernova feedback leaves a strong imprint on the star formation process. We
find an overall reduction of the star formation efficiency by a factor of 2 and
of the star formation rate by roughly factors of 2-4.
