evidence: While rapid loss of sea ice is the primary threat to the polar bear’s long-term survival, other challenges include pollution, increased commercial and industrial activity in the Arctic, overharvest, disease, and inadequate habitat protection (denning and seasonal resting areas). [...] We have never had firm numbers on the global population of polar bears. We do know that some polar bear populations, like those that I studied in Alaska for 30 years, were known to have grown after excessive hunting was controlled in the early 1970s. But we only recently have developed estimates of several populations and still have no estimates for others. Regardless of how many bears may have been around at times past, however, as long as temperatures warm and sea ice habitat continues to decline, polar bears ultimately can only decline. Wild polar bears will become extinct unless we take action to reduce greenhouse gas emissions. [...] Polar bears rely on sea ice to efficiently catch their main prey, ice seals. Although seals can out-swim polar bears underwater, bears have the edge on top of the ice—using it to sneak up on and stalk their next meal. Ice seals, and related ice-dependent species like the walrus, rely on sea ice for survival, too. They use it to rest on and as a platform for giving birth to and raising their pups.