Polar bears are undergoing hunger in a world (warm) than ever before.
Polar bears live in the environment too cold for most animals. For most of the year, they live and hunt on Arctic sea ice. Nature has prepared (they) for the cold conditions. But nothing has prepared the bears for the danger threatens (威胁) their only home.
Polar bears' world is melting. Studies show that polar ice (reduce) by 9.8% every 10 years since 1978. Now about 20,000 to 25,000 polar bears live in the Arctic. Polar bears depend sea ice for their (survive). "Sea ice is more than just the platform that the bears walk over," says Andrew Derocher, scientist who studies North American polar bear populations. "Without it, they can't exist."
(melt) and refreezing of polar ice is natural. But in a warmer world, the cycle speeds up, and polar bears have less time (hunt). Normally, they have three months in the spring when they gain more weight. The extra fat will be used, when the bears are not (active) hunting.
