They stand up to three metres tall, can weigh a tonne fully grown, and have a set of menacing canine teeth superbly engineered for one thing - eating meat. Unfortunately that includes humans. Sadly, climate change is melting the Arctic pack ice where they live and hunt. Faced with starvation, these formidable killers are now encroaching on tiny frontier settlements like Churchill in Canada. Denham Hitchcock visited this polar bear capital of the world and got a little too close for comfort in a frightening encounter on the ice.