Background
Millennial-scale climate cycles have been reported in numerous Holocene proxy records.  Some of these records report cycles of similar frequency, while others reveal different patterns of variation, raising the question of whether climate change during the Holocene has been predominately regional or global in scope.

What was done
In an effort to shed more light on the subject, Nederbragt and Thurow examined a high resolution marine sediment core taken from the Santa Barbara Basin (SBB), off the coast of California, USA, to determine if the millennial-scale climate cycles observed in the Atlantic Ocean were also present in the Pacific Ocean.

What was learned
Cross spectral analyses revealed the presence of two dominant millennial-scale cycles in both the North Atlantic and Pacific SBB sedimentary records at frequencies of ~1000 and 2750 years.  They also demonstrated that these frequencies are similar to frequencies derived from a record of atmospheric Delta¹⁴C that is typically used as an indicator of solar activity.

What it means
The coherence between the North Atlantic, Pacific SBB and atmospheric Delta¹⁴C records strongly suggests, in the words of the authors, that "part of the climate variability during the Holocene is the result of variation in solar irradiance as an external forcing mechanism."  We further believe that it is this millennial-scale climatic variability, forced by some type of solar variability of comparable timescale, that is primarily responsible for producing the Roman Warm Period, Dark Ages Cold Period, Medieval Warm Period, Little Ice Age and Modern Warm Period, and that variations in the air's CO2 content have absolutely nothing to do with the waxing and waning of these alternating warm and cool climatic states.