2.7 million years ago permanent ice showed up in the Northern hemisphere and the ice cap on Greenland started to build up. It was the same time the genus homo appeared on earth. The Quaternary was a time period of high climatic variability.

Glacial and interglacial

After genus homo had started to populate the planet, our ancestors mainly lived in Africa for a long time. The earth’s climate had become variable and relatively cold. On time scales of several tens of thousands of years it had started to oscillate between cold glacials (ice age) and relatively warm interglacials. The ultimate causes and mechanisms triggering these oscillations were not fully understood for a long time. However it was postulated by Milutin Milankovitch, a Serbian astronomer, that variations in the earth’s orbit around the sun and subsequent fluctuations in the heat received over specific areas of the globe cause the transitions between glacials and interglacials. (Imbrie and Imbrie, 1979)

Holocene – interglacial

We currently live in an interglacial, the so called Holocene. During an interglacial the distribution of ice on the continents is comparable to today with large ice caps only existing near the poles in Antarctica and Greenland, respectively.

Glacial and last glacial maximum

Contrastingly, during a glacial, massive ice sheets covered North America and Scandinavia. Global mean temperatures during the last glacial maximum, 20.000 years ago, were estimated to be lower by 4°C than today (CLIMAP, 1981). More recent studies even estimate it was 6°C colder. In response to that the vegetation cover looked completely different.

References:

Wikipedia https://de.wikipedia.org/wiki/Seitenmor%C3%A4ne

Imbrie, J. and Imbrie, K. P., 1979. Ice ages : solving the mystery. Short Hills, New Jersey Enslow, New Jersey.

CLIMAP, 1981. Seasonal reconstructions of the Earths surface at the last glacial maximum. Map series, technical report mc-36, Geological Society of America.