date: Fri, 24 Jun 2005 17:05:14 -0600 from: Raimund Muscheler subject: solar activity to: k.briffa@uea.ac.uk Dear Keith, Caspar Ammann told me that you are coordinator of the discussion about climate change during the last 1000 years. There are conflicting results about the changes in solar activity during the last 1000 years (e.g. Bard et al., 2000, Usoskin et al., 2003) with potentially important implications for the discussion of the influence of natural causes on the current climate change. Therefore, we discussed the radionuclide-based evidence of past changes in solar activity and the reasons for the conflicting results. We also included new calculations about past changes in the 14C production rate that we could connect to the instrumental data. Caspar said that you might be interested to see the paper (I attached the title & abstract below). Best regards Raimund Title: Changes in solar activity during the last 1000 years inferred from radionuclide records Abstract: Identification of the causes of past climate change requires detailed knowledge of one of the most important natural factors - solar forcing. Prior to the period of direct solar observations, radionuclide abundances in natural archives provide the best-known proxies for changes in solar activity. Here we present two independent reconstructions of changes in solar activity during the last 1000 years, which are interred from 14C and 10Be records. These records exhibit a good agreement that allows us to obtain a reliable estimate of past solar magnetic modulation of the radionuclide production rates. Differences between 10Be records from Antarctica and Greenland indicate that climatic changes have influenced the deposition of 10Be during some periods of the last 1000 years. The radionuclide-based reconstruction of past changes in solar activity does not always agree with the sunspot record, which indicates that the coupling between those proxies is not as close as has been assumed by some authors. The tree ring 14C record and 10Be from Antarctica indicate that recent solar activity is high but not exceptional with respect to the last 1000 years. Raimund Muscheler National Center for Atmospheric Research Climate and Global Dynamics Division - Paleoclimatology 1850 Table Mesa Drive Boulder, CO 80305-3000 USA tel: 303-497-1399 fax: 303-497-1348 email: raimund@ucar.edu