evidence: Across recent history, the sea ice was generally stable, thick and not noticeably in retreat. With stable habitat, polar bears were a renewable resource that could be harvested on a sustainable basis. [...] Polar bears depend on the sea ice surface to efficiently catch their seal prey. A shorter duration of ice cover over their productive hunting areas means less opportunity to hunt. A reduction in sea ice has been statistically linked to reduced stature and weight in polar bears and to lower survival rates of cubs. So, it doesn't really matter that hunting is now largely under control or that we know a lot about other impacts people might have on bears. Without habitat, polar bears will disappear no matter what else we do. [...] Planetary physics requires the world to warm as greenhouse gas concentrations rise, so without greenhouse gas mitigation, the ice will continue to melt. For an animal dependent on sea ice to survive, the prospects are not good. As the ice decline continues, the plight of the polar bear can only worsen.