Species like polar bears might go extinct if, for example, sea level rise drastically decreases the size of their territory meaning they have less area to roam, hunt and mate in so they cannot reproduce fast enough to maintain their species' size. Others, such as those living in forests in Britain, might go extinct in major climate warming if desertification were to happen, meaning the plant species they rely on for food and shelter would die and they would be lacking in essentials for successful survival and reproduction.