  The influence of solar variability on climate is currently uncertain. Recent
observations have indicated a possible mechanism via the influence of solar
modulated cosmic rays on global cloud cover. Surprisingly the influence of
solar variability is strongest in low clouds (<= 3km), which points to a
microphysical mechanism involving aerosol formation that is enhanced by
ionisation due to cosmic rays. If confirmed it suggests that the average state
of the Heliosphere is important for climate on Earth.
