Polar bears are suffering in a

　　61

　　(warm) world than ever before.

　　Polar bears live in environments too cold for most animals.

　　62

　　much of the year, they live and hunt on the frozen Arctic sea ice. Nature has prepared

　　63

　　for the cold conditions. But nothing has prepared the bears for the danger that

　　64

　　(threat) the only home they know.

　　The polar bears’ world is melting. Studies show that the polar ice has reduced by 9.8% every 10 years

　　65

　　1978. Now about 20,000 to 25,000 polar bears live in the Arctic. Polar bears depend on the sea ice for their

　　66

　　(survive). “The sea ice is more than just this platform that the bears walk over,” says Andrew Derocher,

　　67

　　scientist who studies North American polar bear populations. “

　　68

　　it, they can’t exist.”

　　Some melting and refreezing of the polar ice is natural.

　　69

　　in a warmer world, these cycles speed up, and bears have less time to hunt. Normally, they have three months in the spring when they gain more weight. The extra fat is used later,

　　70

　　the bears are not actively hunting.

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