Attention nature photographers: If you've been thinking about getting some snaps of polar bears, we suggest you make your travel plans and get on it. According to wildlife biologists with the U.S. Geological Survey, most polar bears will disappear by 2050. To be precise, about two-thirds of the polar bear population will be lost by then, due to the melting of Arctic sea ice. Just thought you'd like to know. By the way, the photograph here was made by nature photographer Thomas Mangelsen and can be found on his website. Tom has one of the truly great collections of polar bear photos.