It is not only penguins that are in danger from changes to the weather. Polar bears are in trouble too. There have been polar bears in the Arctic for thousands o years. They are often 2 metres tall or more, and as heavy as 300 kilos. Their big feet help them to walk across snow and ice, and they are very good swimmers too. The most important food for bears is seals. bears wait quietly near holes in the ice where the seals come up. When they can smell a seal, they pull it out of the water, kill it and eat it. If they eat a lot of seals in the winter months, they can live with little or no food in summer. But things are changing. The Arctic ice is melting earlier in the spring now perhaps three weeks earlier so the bears have less time to hunt for, and eat seals. Then in the autumn the hungry bears have to wait longer before they can swim back to the ice. Today's bears are thinner, and they are not as heavy. In just twenty years the number of polar bears has gone from about 32,000 to 25,000. Why is the ice melting? Global warming which means a change to warmer weather all over the world is happening everywhere. People drive cars, travel in planes, burn forests, and keep animals and all of these things help to change our weather. So scientists say that in a hundred years from now perhaps there will be no more polar bears in the world.