Raimund Muscheler

There is a variety of different cosmogenicradionuclide-based reconstructions of solar activity varia-tions for the past. Especially the longer-term changes andthe absolute levels of past solar activity are uncertain as it isillustrated by the differences between these reconstructions.On the one hand there are differences between10Be and14Crecords that are commonly used as proxies for the varying so-lar modulation of galactic cosmic rays. On the other hand es-timates of past changes in the geomagnetic shielding also in-clude relatively large uncertainties. Here, we concentrate onvariations in cosmogenic radionuclide records on time scalesof 50 to 500 yr. We show that these are to a large extentindependent of the geomagnetic field intensity. The rangeof variability of cosmogenic radionuclide records allows usto set constraints about long-term changes in solar activity.These records indicate that present solar activity levels werereached or exceeded regularly in the past