From @cnnclimate: Polar bears rely on sea ice for nearly every aspect of their survival, and with ice beginning to melt earlier in the season, these animals are becoming thinner and having fewer cubs, according to a new study. Polar bears “are an icon of climate change, but they're also an early indicator of climate change because they are so dependent on sea ice,” writes Kristin Laidre, the study’s author and a professor at the University of Washington. Polar bears are considered a vulnerable species, one level below "endangered." Their future, the researchers write in their findings, depends on scientists' ability to predict how climate change will continue to impact the bears. (:Paul Souders/Getty Images)