Global warming has a great influence on species all over the world. Polar bears are particularly at risk because their habitat is increasingly threatened by global warming. Lots of scientific research has shown that polar bear numbers are on the decline, and that if action is not taken quickly, polar bears may die out from the Earth. Pack ice  is decreasing globally. In the wild, polar bears spend much of their lives wandering pack ice in search of food. In 2009, several polar bear deaths by drowning were recorded, which had never been heard of before. The polar bears had been trapped on isolated areas of floating ice, and had tried to swim for land. Due to the shrinkage of the ice, the polar bears tired and drowned before reaching the shore, though they are rapid and aggressive swimmers. This problem will only grow as the pack ice shrinks. The shrinkage of the ice has other consequences for polar bears. They are losing their natural prey , who are also affected by the shrinkage in habitat. Land animals also do not provide the high-fat diet that polar bears need, which will lead to starvation. Starving mothers will not be able to provide their babies with the nutrition they need, which will further contribute to the decline in polar bear numbers. While searching for food and habitat, polar bears have also fought with humans. With the disappearance of the sea ice, polar bears have begun to show up around inhabited areas looking for food and shelter. But they often end up being killed by hunters because they present a threat to human communities. The combination a deadly factors brought about by global warming put polar bears at a very high rate of risk. A global effort is needed to act against global warming before it is too late for polar bears, as well as many other species that call Earth home. This text is mainly developed by   _  .
analyzing causes and effects making comparisons examining differences giving examples