The great ice sheets that covered much of the northern hemisphere had been growing for thousands of years.

In North America, the Laurentide Ice Sheet reached south into what is now the northern United States, burying the landscape under ice a mile or more thick.

In Europe, glaciers extended far south of the modern ice line.

The global climate was colder and drier than today, sea levels were dramatically lower because so much of the world’s water was locked in glacial ice, and the landscape of Siberia — never warm even in interglacial periods — was an extreme environment even by its own historical standards.

The area around Lake Baikal was not glaciated itself — the interior of Siberia was too dry for the massive snowfall that feeds continental glaciers.