Solar activity over the last 1150 years: does it correlate with climate?
Sami K. Solanki (MPI für Sonnensystemforschung, Katlenburg-Lindau, Germany)
Ilya Usoskin (Sodankyla Geophysical Observatory, University of Oulu, Finland)
Manfred Schuessler (MPI für Sonnensystemforschung, Katlenburg-Lindau, Germany)
The sunspot number is the longest running direct index of solar activity, with
reliable measurements starting in 1610. For many purposes it needs to be
extended, however. This would benefit, in particular, from comparisons with
climate indices. We present a reconstruction of the cycle averaged sunspot
number over the last millennium based on 10Be concentrations in Greenland
and Antarctic ice. We expect this reconstruction to be close to an upper limit
to the correct sunspot numbers, particularly for the earlier times. Our
reconstruction agrees very well with the direct measurements during the last 3
centuries (although the values are slightly higher during the Maunder
minimum). The full reconstructed sunspot number series shows all the known Grand
Minima (Maunder, Spoerer, Wolf, etc.) and the medieval maximum. However, the
most striking feature of the reconstruction is that during the last 1150 years
the Sun was never as active as during the last 60 years. We present a comparison
with the Mann et al. "hockey stick" curve for global temperature and find a
reasonable correspondence, if we neglect the last 2 decades. In particular the
sunspot number exhibits a gentle decreasing trend over most of this period
followed by a rapid increase in the last century. During the last 2 decades,
however, the cycle-averaged sunspot number has remained basically constant,
while the temperature has continued to increase.
www.linmpi.mpg.de/~solanki