Direct observations of sunspot numbers are available for the past
four centuries1,2, but longer time series are required, for example,
for the identification of a possible solar influence on climate and
for testing models of the solar dynamo. Here we report a
reconstruction of the sunspot number covering the past 11,400
years, based on dendrochronologically dated radiocarbon concentrations.
We combine physics-based models for each of the
processes connecting the radiocarbon concentration with sunspot
number. According to our reconstruction, the level of solar
activity during the past 70 years is exceptional, and the previous
period of equally high activity occurred more than 8,000 years
ago.We find that during the past 11,400 years the Sun spent only
of the order of 10% of the time at a similarly high level of
magnetic activity and almost all of the earlier high-activity
periods were shorter than the present episode. Although the
rarity of the current episode of high average sunspot numbers
may indicate that the Sun has contributed to the unusual climate
change during the twentieth century, we point out that solar
variability is unlikely to have been the dominant cause of the
strong warming during the past three decades3.
http://mirage.mps.mpg.de/projects/solar-mhd/pubs/solanki/Solanki_et_all_2004_nature.pdf