  The extension of the sunspot number series backward in time is of
considerable interest for dynamo theory, solar, stellar, and climate research.
We have used records of the Be-10 concentration in polar ice to reconstruct the
average sunspot activity level for the period between the year 850 to the pr
esent. Our method uses physical models for processes connecting the Be-10
concentration with the sunspot number. The reconstruction shows reliably that
the period of high solar activity during the last 60 years is unique throughout
the past 1150 years. This nearly triples the time interval for which such a
statement could be made previously
