Ice ages occur periodically due to a combination of continental location, atmospheric concentration of gasses, and solar input.
Over the last ~2.5 million years, we have been in the Quaternary glaciation, one of five ice ages in Earth’s history. During this period, we cycle through glacial and interglacial periods. Ice sheets expand and contract on the order of tens of thousands of years. These ice ages are controlled to a large extent by Milankovitch Cycles.
In her book the Left Hand of Darkness, Ursula Le Guin explores a planet set in an ice age. The last third of the book takes place on a trek across one of the polar ice sheets.
Return to syllabus
In case you ever feel lost, or want to jump, here’s a map.