Overview of the Various Models for Ice Ages
Solar: Variations in the innate solar intensity due to structural variations within the Sun may have caused glacial-interglacial cycles.
Astronomical Theory: Quasi-periodic variations in eccentricity , obliquity and precession of the equinoxes produce changes in solar intensity to higher latitudes that cause glacial-interglacial cycles.
Volcanism : Volcanism causes temporary changes in the Earth’s response to the Sun that may trigger initiation of longer-term glacial-interglacial cycles.
Greenhouse Gases : Variability of concentrations of greenhouse gases (particularly CO2 and CH4) induced by unspecified events have been conjectured to be a cause of glacial-interglacial cycles via changes in the greenhouse effect.
The Oceans: Variability in the thermohaline circulation of the oceans producing large changes in heat delivered to higher latitudes has been hypothesized to cause glacial-interglacial cycles.
Extraterrestrial Accretion: Several models are based on effects due to quasi-periodic accretion of extraterrestrial dust in the Earth’s atmosphere as the primary forcing that induces changes in cloud cover that in turn, affects the climate.
Ocean-Atmosphere Interactions: In this model, the primary factor that controls large-scale variations in the Earth’s climate is the albedo of the Earth, which in turn, is controlled by the degree of cloudiness which goes through repetitive cycles due to ocean-atmosphere interactions.