What Are the Chances of a Global White Christmas?

From holiday films to children's books, Christmas seems to be perennially tied with snow. But dare we dream of such a winter wonderland across the globe? The prospects are enticing and may reside in more than fairy tales, scientists say.

They can certainly keep dreaming, because climatologists say that it's not impossible. But don't bet all the holiday gifts under the tree on the chance of a snow-blanketed Earth this Saturday.

"Is it possible that snowfall can occur across the entire Earth? If the temperatures are low enough and if there is an excess of humidity present, then it can," said Caspar Ammann, a scientist at the National Center for Atmospheric Research (NCAR) in Boulder, Colo. "Is it likely? No."

Every part of the globe may have at least seen snow on the ground at some point during Earth's existence, Amman explained, but not during human history. Continue ►