Most polar（北极）bears could disappear by the end of the century because of global（全球）warming, scientists say.

According to a study in Nature Climate（气候）Change, the number of most polar bears will_ 21_rapidly by 2080. There are two reasons. One is that the sea ice is melting（融化）. Polar bears catch seals（海豹）to eat on the ice. 22ice, they have to stay on land. But there is no_ 23food on land to support so many bears. The animals could die from hunger. The other reason is that mother bears may not be fat enough to _ 24milk for their babies, so some bears could stop having babies.

Polar bears are_ 25_land animals that eat meat on the planet. They help control other kinds of animals. Losing them would break the balance of their living place.

The Arctic（北冰洋）is the_ _26_to about 25, 000 polar bears. Arctic sea ice usually melts in spring and summer, then grows in winter. But now, the 27is taking longer to grow back. Scientists say the Arctic is warming twice as fast as the rest of the planets.

The study also shows 28it is possible to slow Arctic melting. Greenhouse gas（温室气体）could lead to climate change. In order to avoid creating greenhouse gas, the world should try to stop burning coal and riding in cars.

Saving the bears is _ 29us. Holland, one of the writers of the study, says, "I believe there is hope, but humans need to act 30to make that hope come true. "Let's take action to protect our earth and save polar bears.

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