What were the primary forcing mechanisms of high-frequency Holocene climate and glacier variations?

A compilation of Holocene glacial advances throughout the world is compared with summer solar insolation integrated over the Northern Hemisphere and the magnitudes of global acid fallout from volcanic eruptions north of 20 degrees S estimated from the acidity signal of annual ice layers in the Crete and Camp Century ice cores in Greenland. Correlation analysis between glacial advances versus volcanic eruptions yielded a correlation coefficient of r = 0.71. A 'climatic forcing' curve (solar insolation and volcanic eruptions weighted 1:1) versus glacial advances increased the correlation coefficient to r = 0.90. This suggests that the combined effect of volcanic aerosols and orbital-related Northern Hemisphere summer insolation may have been the primary forcing mechanism of worldwide climate and glacier fluctuations throughout the Holocene.