What percentage of the worlds population has a White Christmas?

Of those who celebrate it, the vast majority have a high potential of it, since the vast majority of the world's population is in the Northern Hemisphere where it is winter in December.

In spite of us mostly being northwards, I think that not many actually experience many White Christmases in our lifetimes. I am 63 years old, in Britain, and from fallible memory I would say less than a third have been white. New Years - rather more.