In the series that shows present day earth going backwards, why when the ice age is shown only the ice sheet at the North pole is enlarged? Shouldn't the ice sheet at the South pole increase in size as well?
It does; you can see ice over the tip of South America. Note that the ice in the southern hemisphere extends about as far from the pole as that in the northern hemisphere. There's just a lot less ice in the southern hemisphere because there's less land at those latitudes.