The Sun's Role in Climate
Abstract Millennial scale climate variability is a globally well established Holocene phenomenon described for all oceans and continents. Cycles are known from upper, middle, and lower latitudes, encompassing all climate zones from the Arctic to the tropics. The amplitude of the observed temperature fluctuations is often more than 1degC and thus has a similar or even greater range than the warming that has occurred since the Little Ice Age. Furthermore, many of these Holocene, natural climate fluctuations show the same level of abruptness as the 20th century warming. A common characteristic of many of the documented millennial climate fluctuations is their good match with solar activity changes, as well as a North Atlantic climate record by Bond et al. (2001) Besides solar activity changes, internal millennial ocean cycles may have contributed to the observed climate oscillations. Both solar and internal climate system autocyclical drivers are not yet fully implemented in the current climate models, which still do not manage to reproduce the variable Holocene climate development. Yet successful hindcast capability is generally considered a prerequisite that qualifies models to be used for modeling of future climate. This chapter reviews Holocene millennial scale climate fluctuations as reported in 64 papers worldwide. Future research needs to attempt a detailed correlation of the existing Holocene climate curves, complemented by additional data sets filling gaps in currently poorly documented regions. A good understanding of global Holocene millennial and centennial scale climate variability and its possible solar forcing is required as a calibration basis for a new generation of climate models that should have the objective to reliably reproduce past climate change before attempting detailed future simulations.