I've read in one website that 90% of the Earth's population are in the northern hemisphere. It's logical as it is because of the land mass concentration.
For the northern hemisphere theme for Sunday Stamps this week, here are stamps from China -- the most populous country on Earth. The stamp design on the left is from the Huangmei Opera set of 3. The two other designs and the description of the series can be found here. On the right is of the Prime Minister Zhuge Liang. This design is called Devotion to Service. Information about the rest of the sheet can be found here. For the prime minister, here.