Old sea ice has almost vanished

Arctic sea ice is getting younger, thinner and less stable. While Arctic sea ice comes and goes with winter freezing and summer thaw, a significant portion of Arctic sea ice once remained through the Arctic summers, surviving from year to year. Ice older than 4 years old used to make up over 30% of the Arctic Ocean, but it now makes up only 3.1 percent of the ice cover. Further, thin first-year ice now makes up the majority of the Arctic Basin, making it more vulnerable to melting out each summer.