It’s not easy to swim 175 km (109 mi.) when you’re starving to death. It’s not easy either to try to survive when you’re shedding body weight at a rate of 1 kg (2.2 lbs.) a day. And it might be hardest—or at least most tragic—of all if you’re a nursing mom and your calorie intake has dropped so low that you can no longer produce the milk you need to care for your young. As a new paper in Nature Communications reveals, all of those challenges and more are facing the world’s polar bears, thanks to vanishing sea ice in our warming world, denying the animals a platform that they need to hunt for seals. If the trend isn’t reversed soon, the estimated 26,000 polar bears in the wild could start to lose their hold on survival before the middle of this century.