An arctic seal species is threatened as two thirds of sea ice with enough snow cover for them to reproduce is at risk of disappearing, U.S. researchers say. Scientists as the University of Washington say the ringed seal, under consideration for threatened species status, needs to build caves to rear its young in snowdrifts on sea ice. \"It\'s an absolute condition they need,\" atmospheric science Professor Cecilia Bitz said in a university release. Snow depths must average at least 8 inches to enable drifts deep enough to support the caves, the researchers said. But as sea ice, the platform that allows the snow to pile up, disappears with climate change, it reduces the area where the seals can raise their pups. With disappearing sea ice, snow in the fall -- the heaviest snowfall period -- will fall into ocean water instead of piling up on ice, the researchers said. The area of the arctic that received at least 8 inches of snow will decrease by almost 70 percent this century, they estimate, and with insufficient snow depth seal caves won\'t hold up.