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Unusual activity of the Sun during recent decades compared to the previous 11,000 years

First released image from the NOAA GOES-12 Solar X-ray Imager (SXI) on September 7, 2001, courtesy of NOAA Space Environment Center Unusual activity of the Sun during recent decades compared to the previous 11,000 years
Nature, Vol. 431, No. 7012, pp. 1084 - 1087, 28 October 2004.

S.K. Solanki1, I. G. Usoskin2, B. Kromer3, M. Schüssler1, and J. Beer4

1 Max-Planck-Institut für Sonnensystemforschung (formerly the Max-Planck- Institut für Aeronomie), 37191 Katlenburg-Lindau, Germany
2Sodankylä Geophysical Observatory (Oulu unit), University of Oulu, 90014 Oulu, Finland
3Heidelberger Akademie der Wissenschaften, Institut für Umweltphysik, Neuenheimer Feld 229, 69120 Heidelberg, Germany
4Department of Surface Waters, EAWAG, 8600 Dübendorf, Switzerland
Direct observations of sunspot numbers are available for the past four centuries, 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 decades.

Download data from the WDC Paleo archive:
11,000 Year Sunspot Number Reconstruction

Figure 3a. 10-year averaged SN reconstructed from d14C data since 9500 BC (blue curve) and 10-year averaged group sunspot number (GSN) obtained from telescopic observations since 1610 (red curve).
To read or view the full study, please visit the Nature website.
It was published in Nature, Vol. 431, pp. 1084 - 1087, 28 October 2004.

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2 February 2005