Estimates range from 2013-terrifyingly soon-to 2050 for the first year when the Arctic is free of ice in summer.
据推测，北极夏日无冰的开始年份，最早为急迫的2013年，最晚2050年。
3
Summer sea ice is vital to a range of Arctic marine and land animals, and its annual summer melt-off is projected to increase dramatically as the climate warms.