Thank you very much for your question! Polar bears are not extinct, but they were listed as 'threatened' under the Endangered Species Act in 2008. Being threatened with extinction means that scientists have observed that polar populations are declining, and that the decline is likely to continue in the future. The most common cause of extinction has been loss of habitat. Scientists use the word habitat to describe the type of environment in which an organism or group normally lives or occurs. It is thought that the reason for the declines in polar bear populations is to do loss of habitat. Polar bears spend most of their time on, or near sea ice in the Arctic. They hunt for seals at the edges of the ice, and at holes in the ice where seals need to come up for air. So, the number of polar bears is very tightly linked to the number of seals and the amount sea ice from which to hunt. The amount of sea ice in the Arctic Ocean has been declining for years; it also has been freezing slower in the winter and melting more quickly in the spring. This means that not only is there less area for polar bears to hunt from, there is less time do it in as well. As you can imagine, life in the Arctic is very hard. Anything that makes it harder for polar bears to find food means that more bears are likely to starve, and female bears are likely to have fewer cubs. It is conditions like these that can lead to declining populations, even extinction if the conditions get worse or don't improve. Fortunately, lots of people from the United States and many other countries are working hard to better understand what polar bears need to survive and thrive, and how humans can help them to recover. We know more than we did just a few years ago, and we will know even more in the future. I hope this answers your question. Keep them coming!