For a polar bear, winter's first snow is a sign that it's time to make a den--a safe place for her to sleep through the harsh season and give birth to her cubs. When they wake up, she will guide them on a journey to the sea ice, where she will teach them to hunt. But the Arctic is changing; familiar landscapes are melting. What kind of world will her cubs grow up in? The story's clear text and gorgeous, affecting illustrations capture the massive bear's movements amid a crystalline landscape, while quietly observing the loosening ice and other effects of climate change on her life and that of her active cubs. Back matter offers more information and suggestions on how we can help protect the planet for these majestic animals.