Pleistocene volcanism and glacial initiation.
During the past 2 million years, major Northern Hemisphere eruptions occurred within 0.01 million years before 22 of 24 maximum-temperature dates which preceded the ten European glacial stages and 42 of 60 maximum-temperature dates which preceded the 22 cooling episodes. Massive eruptions were even more closely associated with the glacial stages and the cooling episodes. Within the errors of Pleistocene dating, major eruptions apparently occurred at the crucial moments to have triggered each of the ice ages.
Bray
J R
JR