Approximately 20,000 years ago (around the end of the last ice age), an unknown even took place in the southern hemisphere, causing it to warm up. Though it does not have much differences or change on the remainder of the world, it's biggest impact is on Antarctica, in which the continent begins to warm to the point that its large-scale icecap melts, and remain ice-free for millennia to come.
Though much warmer than in OTL, Antarctica remains a tundra not much different than Alaska, Iceland, Northern Scandinavia or Siberia. Ice continues to cover the region around the south pole, and a small-scale icecap does continue to exist on the continent. Despite the fact that Antarctica remains cold and dark, it is now habitable for humans, who arrived around 10,000 years ago. There is farming and crop growing in the most northerly areas and extensive fishing in the seas surrounding the continent.