This cave in Canada remains frozen every summer—and it's been frozen since the last Ice Age 10,000 years ago. What can this tell us about Earth's future climate? Stream "Polar Extremes" on the PBS app or online now: https://to.pbs.org/2wcgxe6 | NOVA l PBS

The ice in the Arctic and Antarctica plays critical roles in maintaining life on Earth. They are the biggest reservoirs of freshwater on the planet and help steer ocean currents, which are major drivers of our weather. But if enough of that ice melts, sea levels could rise all over the world. That’s why a team of scientists is studying the Thwaites Glacier, nicknamed the "Doomsday Glacier," which is roughly the size of Florida and melting fast. PBS News Hour’s science correspondent Miles O’Brien