In 1960 the estimated polar bear population was 10,000 (+- 5,000). The latest estimate is 39,000 of the creatures, the largest ever recorded.

This is due to a combination of a hunting ban, but also due to an increase in seal population, the bears' primary food source. Less ice and more open water stimulates the growth of phytoplankton, which are the entire basis of the food chain in the Arctic Sea. If there is more phytoplankton there will be more zooplankton that feed on them, and if there is more phytoplankton there will be more fish. If there are more fish there will be more seals, and if there are more seals there will be more polar bears. That's how the food chain works.

Moore, Dr. Patrick. Fake Invisible Catastrophes and Threats of Doom (pp. 84-85).