Email 3099, July 2001, Keith Briffa, HIHOL report: "there is a growing number of striking coincidences between climate changes and the occurrence of abrupt changes in solar activity such as grand minima"

Email 3099

During the 24-26 October 2000, 42 scientists from 13 countries gathered to attend the meeting of HIHOL (High Resolution Variability in the Holocene) held in L'Isle sur la Sorgue, near Avignon, France, with the support of PAGES, SCAR and NSF...Long term reconstructions of solar activity are based on proxies such as sunspots, aurorae and the geomagnetic aa-index, but are limited to the past centuries. These proxies show a generally increasing trend since 1600 AD which is interrupted from time to time by short periods (50-100 y) of low solar activity. The most prominent one is the Maunder minimum (1645-1715 AD) a period which is characterised by an almost complete absence of sunspots. Records of cosmogenic nuclides in ice cores (10Be, 36Cl) and tree rings (14C) reveal longer cycles of solar variability (e.g. 90 and 205 years) and several grand minima, periods when the sun was quiet as during the Maunder minimum. Since the physics of the relation between solar activity and solar irradiance is not yet fully understood it is premature to derive a solar forcing function in W m-2. However, there is a growing number of striking coincidences between climate changes and the occurrence of abrupt changes in solar activity such as grand minima.