Polar bears in many ways have become the symbol of climate change. In 2008, they were listed as a threatened species under the Endangered Species Act -- the first species to be listed because of forecasted population declines from the effects of climate change. The primary cause of their decline: loss of sea ice habitat attributed to Arctic warming. Polar bears need sea ice to hunt seals -- a main source of food -- as well as to move across the large home ranges they need for foraging habitat. Polar bears aren’t alone in feeling the effects of shrinking sea ice. Walruses and other Arctic species are facing similar challenges as summer sea ice continues to retreat. Photo by National Park Service.