According to an episode of David Attenborough's Planet Earth (only reference I could find is here), a third of Earth's land is covered by deserts. I just cannot believe this.
Yes, there is plenty of desert, but a third? The Antarctica, Greenland, Canada, Siberia, which are pretty big, are mostly not deserts. Or am I wrong? If this is true, it would mean that population density is pretty high in the other two thirds of the land, as allegedly few people live in deserts.