Final answer:
Ice ages are primarily attributed to the tilt of Earth's rotational axis, changes in Earth's orbit, volcanic eruptions, and variations in solar activity.
Step-by-step explanation:
The ice ages of the past were most likely primarily caused by a few main factors. One significant cause is the changes in the tilt of Earth's rotational axis and its orbit due to the gravitational effects of other planets. Such changes affect how sunlight is distributed on Earth's surface and can lead to periods of cooling.
Another possible cause for these periods of global cooling, particularly the Little Ice Age during the fourteenth century, includes volcanic eruptions which release aerosols into the atmosphere, reflecting sunlight away from Earth and thereby reducing temperatures. Additionally, variations in Earth’s orbit and solar activity also play a role in climate change over long periods, contributing to the advance and retreat of ice sheets and glaciers.