Some 20,000 years ago marks the end of the "Warm Age" were Earths surface temperatures where its hottest since its formation. Due to this event the world remains covered in sheets of ice that cover most of Eurasia, and North America as well as greatly expanding the land mass of Antarctica. Most of North America is covered in ice all the down to OTL Kansas and nearly all of Russia, and Scandinavia are covered in far more ice; at least enough ice to make them barren uninhabitable glaciers, and completely shrouds the British and Irish isle in nothing but ice.
There are massive land-bridges that connect both Europe and Asia to North America allowing primitive hunter gatherers from both continents to settle in the Americas. For a brief time there is also a land bridge that connects South America and Antarctica only few native Americans cross this land bridge and settle in Antarctica populating it at the same amount of OTL Inuits. Due to the colder temperature many more primitive humans died because they where unable to adapt, as a result Earths population is about 4.84 billion.