The series returns with a visually stunning dispatch from the far corners of the world, as CNN's Chief Climate Correspondent Bill Weir follows the humpback whale migratory journey from Antarctica all the way to the coast of Colombia. Humpback whales have the longest migration route of any mammal on earth, and in this immersive episode, Weir embeds with a team of researchers as they venture from Antarctic ice to rich South American jungles, hoping to discover the impact of climate change on these magnificent creatures. While humpback whales have made a spectacular comeback in the last fifty years and are considered a beacon of modern conservation, they are now having to face some of the biggest existential threats of all. On this journey, Weir confronts one of the last of the whale hunters in Iceland and while climate change deniers blame offshore wind development for a spate of dead animals washing ashore, he digs for the truth with some of the leading experts in the world. Amid the striking landscapes and diverse coastlines, Weir also learns how whales have the ability to absorb and store carbon, making them one of our greatest allies in the battle against climate change."I was a little boy when recordings of humpback songs sparked a movement to save the whales and reversed a manmade extinction," said Weir. "Fifty years later, artificial intelligence could help us understand the lyrics of those songs just as science realizes the enormous ocean repair services provided by whales. They are literally the biggest allies we have in the fight against climate change, and by saving them, we help save ourselves."