our in-depth report tonight comes from cbs's erin hassanzadeh.estern hudson bay. >> oh, there you go. >> they are putting on quite a show for us today. >> reporter: here on the edge of the arctic, the annual migration of these polar bears draws tourists, photographers. >> they are play fighting. >> reporter: and scientists like geoff york. buggies traverse the frozen terrain bringing tourists closer to something wild. >> what were you expecting? >> to see polar bears. >> looks like we have a mom and a 2-year-old. >> reporter: they pass through churchill, manitoba looking to catch a ride out of the tiny town on hudson bays sea ice. after a summer of fasting on land, the bears need to get back to their frozen homes to hunt seals and bulk up. but this migration ritual is changing. >> the arctic is one of the fastest warming regions on the planet. >> reporter: climate researchers say the arctic is warming nearly four times faster than the rest of the globe according to weather data. climate scientist flavio lehner says it's melting the sea ice bears