Yep. As the ice caps melt, many polar bears have moved south, and due to temperatures in the grizzly bears natural habitat getting warmer, they have moved farther north. Hence, the two bears have met and mated.
If I remember correctly, grolar bears cannot mate with any other bears because they're sterile. I'm not 100% sure about that though.
Yeah, and sterility worked out so well for the Krogan. If they actually are sterile, we not only have powerful, sadistic hybrid bears, we have fatalist bears.
Viking bears. We're screwed.