The Julian Calendar may say December 21st, but to me, this is the start of the New Year. This is the day of the winter solstice, the day when the Earth is at its perihelion, its closest point to the Sun.
Yes, we are closest to the Sun now. So why is it winter in the northern hemisphere? Because the northern half is pointing away from the Sun, thus receiving less heat and light. It is summer in the southern hemisphere, which is actually warmer than summer in the north.
We are definitely exhibiting a northern bias, aren't we?
Buck the trend. Start your year on the winter solstice, not eight to ten days after. Calendars are arbitrary enough, make the starting point of the year meaningful.