The beginning of the current ice age:
The development of Earth’s climate towards the ice age, i.e. the the Quaternary, started during the preceding geological period (Neogene,). Processes like the drift of Antarctica into the position at the South Pole, orogeny in Europe, Asia and along the west side of both Americas as well as the closing of the Isthmus of Panama were steering factors of the long-term climate deterioration, and also induced changes in atmospheric and marine currents.
Furthermore, a cyclic variability of the orbital parameters an therewith the solar forcing developed, with an initial rhythm of 40,000 and later of 100,000 year intensified weathering and the development of new plants such as the so-called C4-plants caused a reduction of the greenhouse gas CO2 in the atmosphere.
In Antarctica, South America, and Northwest Canada evidence of early glaciations exists. Glaciations were named after the development of the middle and late Pleistocene Scandinavian and North-American inland ice sheets as well as the high mountain glaciations, whose sediments and landscape reliefs are still formative elements today.